This PDF file contains the front matter associated with SPIE Proceedings Volume 7122, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We discuss the notion of a 'shared technology roadmap' between lithography and design from several perspectives. First, we examine cultural gaps and other intrinsic barriers to a shared roadmap. Second, we discuss how lithography technology can change the design technology roadmap. Third, we discuss how design technology can change the lithography technology roadmap. We conclude with an example of the 'flavor' of technology roadmapping activity that can truly bridge lithography and design.

Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top critical issues. A survey was created with support from SEMATECH and administered by David Powell Consulting to gather information about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of semiconductor company mask technologists, merchant mask suppliers, and industry equipment makers. This year's assessment is the seventh in the current series of annual reports. With ongoing industry support, the report can be used as a baseline to gain perspective on the technical and business status of the mask and microelectronics industries. The report will continue to serve as a valuable reference to identify the strengths and opportunities of the mask industry. The results will be used to guide future investments pertaining to critical path issues. This year's survey is basically the same as the 2005 through 2007 surveys. Questions are grouped into categories: General Business Profile Information, Data Processing, Yields and Yield Loss Mechanisms, Delivery Times, Returns, and Services. Within each category is a multitude of questions that create a detailed profile of both the business and technical status of the critical mask industry.

This is a report on a panel discussion organized in Photomask Japan 2008, where the challenges about "Mask Complexities, Cost, and Cycle Time in 32-nm System LSI Generation" were addressed to have a look over the possible solutions from the standpoints of chipmaker, commercial mask shop, DA tool vendor and equipments makers. The wrap-up is as follows: Mask complexities justify the mask cost, while the acceptable increase rate of 32nm-mask cost significantly differs between mask suppliers or users side. The efficiency progress by new tools or DFM has driven their cycle-time reductions. Mask complexities and cost will be crucial issues prior to cycle time, and there seems to be linear correlation between them. Controlling complexity and cycle time requires developing a mix of advanced technologies, and especially for cost reduction, shot prices in writers and processing rates in inspection tools have been improved remarkably by tool makers. In addition, activities of consortium in Japan (Mask D2I) are expected to enhance the total optimization of mask design, writing and inspection. The cycle-time reduction potentially drives the lowering of mask cost, and, on the other, the pattern complexities and tighter mask specifications get in the way to 32nm generation as well as the nano-economics and market challenges. There are still many difficult problems in mask manufacturing now, and we are sure to go ahead to overcome a 32nm hurdle with the advances of technologies and collaborations by not only technologies but also finance.

During the development of optical lithography extensions for 32nm, both binary and attenuated phase shift Reticle Enhancement Technologies (RETs) were evaluated. The mask blank has a very strong influence on the minimum feature size and critical dimension (CD) performance that can be achieved on the finished reticle and can have a significant impact on the ultimate wafer lithographic performance. Development of a suitable high resolution binary mask making process was particularly challenging. Standard chrome on glass (COG) binary blanks with 70 nm thick chrome films were unable to support the required minimum feature size, linearity, and through pitch requirements. Two alternative mask blank configurations were evaluated for use in building high resolution binary masks: a binary (BIN) mask blank based on the standard attenuated PSM blank and an Opaque MoSi on Glass (OMOG) mask blank consisting of a newly- developed opaque MoSi [1]. Data comparing the total process bias, minimum feature size, CD uniformity, linearity, through pitch, etch loading effects, flatness, film stress, cleaning durability and radiation durability performance of the different binary and attenuated PSM mask blanks are reported. The results show that the new OMOG binary blank offers significant mask performance benefits relative to the other binary and attenuated PSM mask blanks. The new OMOG blank was the opaque mask blank candidate most capable of meeting 32nm binary mask fabrication requirements..

Aggressive optical proximity correction (OPC) has enabled the extension of advanced lithographic technologies to the 32nm node. The associated sub-resolution features, feature-feature spacings, and fragmented edges in the design data are difficult to reproduce on masks and even more difficult to inspect. The patterns themselves must be differentiated from defects for inspectability, while the ability to recognize small deviations must be maintained for sensitivity. This must be done without restricting necessary OPC design features. The semi-transparent nature of industry-standard 6% attenuated phase shift substrates introduces a host of problems relative to inspectable dimensions and subsequent defect sensitivities. The result is a reduction in inspectability, defect sensitivity and the inability to inspect smaller critical dimensions and OPCed features. The introduction of a binary-type attenuated phase shift film improves the ability to inspect smaller critical dimensions and smaller OPC features without loss of inspectability and sensitivity extending the capability of existing inspection hardware for 32nm ground rule masks. This paper introduces inspection characterization results for this new film, opaque MoSi on glass (referred to as OMOG in this paper) and draws a correlation between the film's transmission qualities and inspectability of 32nm OPC features. The paper will further show a correlation between OPC feature size and defect sensitivity for 32nm ground rule designs. Aerial Image (AIMS) analysis will be used to identify areas where the enhanced inspection capability can be leveraged to avoid unnecessary restrictions on OPC.

Advanced immersion lithography utilizes higher numerical aperture (NA) stepper lenses resulting in higher angles of light illumination through photomasks. Transmission in conventional pellicles (830 nm thickness) is generally maximized at 0 degree illumination and decreases significantly at the higher angles. Most pellicle suppliers have developed thinner pellicle membranes (~280 nm) which allow considerably improved transmission of light at angles up to 20 degrees. In addition, aluminum frames have been shortened, potentially allowing inspection closer to the inside of the frame and reduced mask flatness distortion upon pellicle mount. Suppliers have also developed advanced adhesives which reduce outgassing even beyond the low levels obtained with current 45 nm pellicles. In this paper, advanced immersion pellicles from several suppliers are evaluated and compared with conventional 45 nm pellicles for the following quality parameters: physical durability, foreign material, ease of demounting and glue removal, chemical outgassing, mask flatness distortion and susceptibility to radiation damage. Improvements in mask inspection and pellicle optical transmission at higher incident angles are also evaluated and are discussed.

With tighter CD uniformity requirements, a tighter temperature control during a Post Exposure Bake (PEB) process for photomask production becomes more and more important. CD non uniformities can be partially ascribed to deficiencies of the measurement devices used for the process qualification of a PEB hotplate system. In this paper, a new routine is proposed to overcome the deficiencies of the measurement devices used, so that further improvement of the hotplate performance becomes possible. Using a 25 point sensor array, we finally achieved a bake performance of the hotplate system described in terms of "real" total temperature range on the mask surface, of 0.4°C during temperature ramp-up and below 0.1°C at steady state for a final mean temperature of 100°C. This is a first step in the right direction towards a temperature range of zero for the bake process.

Development process for 3x nm node devices and beyond is becoming a great issue in mask fabrication. The following items, such as uniformity, repeatability, loading effect and defect must be improved. To evolve the development process, TEL, DNP Omron and Toshiba have been jointly developed next generation equipment which is called "Second-generation PGSD (Gen.2)". In this paper, PGSD Gen.2 concept is introduced and its performance is reported.

In order to fulfil the upcoming requirements for photomasks there is a need for improving the process stability (reproducibility) of the unit processes in photomask fabrication. In order to understand and minimize the etch contribution to the CD stability impedance sensors integrated into the capacitively coupled radio frequency (RF) circuit (bias circuit) have shown a big potential. The last step towards a full characterization of the RF properties is the integration of impedance sensors in the inductively coupled RF circuit (source). This kind of sensor measures voltage, current and phase angle for the fundamental (13.56 MHz) and higher harmonics (up to the 5th harmonic). In this paper we are describing the integration of the Z-Scan sensors into the source RF matchbox and its impact on the RF and CD characteristics of the mask etcher. The central point is the correlation of impedance data to CD data. We will also compare the responses for bias and source impedance measurements.

Two key parameters of attenuated phase shift masks are critical dimension uniformity (CDU) and phase uniformity. This study examines the important role that plasma etch plays in determining these parameters. For optimal results, the impact which Cr and MoSi etch have on uniformity must be understood not only individually, but also as a complementary pair. A two-step MoSi etch was developed; the first step was tuned to have a higher etch bias at the edge than at the center, while the second step had a very uniform etch bias. By controlling the fraction of the MoSi consumed by each step, the MoSi etch was adapted to complement the Cr etch and thus optimize overall CDU and phase uniformity.

Reticles have been found to be susceptible to damage by the Electric Field induced Migration of chrome (EFM) at field levels >100x lower than those that cause ESD. The experimental quantification data are reviewed briefly and detailed AFM imagery is presented illustrating the nature of the reticle degradation process. The characteristics of EFM and its very low onset threshold have significant implications for the protection of advanced reticles so a new reticle handling methodology is proposed which is designed to minimize the risk of field induced damage.

Electrostatic protection is an issue for all masks, whether during mask production, shipping, storage, handling or inspection and exposure. Up to now, only manual electrostatic field measurements, or expensive and elaborate analyses with Canary reticles have given hints about the risks of pattern damage by ESD events. A new test device is being introduced, which consists of electrostatic field sensors, integrated INSIDE a closed fused quartz housing which has the outside dimensions of a 6 inch mask. This device can be handled and used like a normal 6 inch reticle. It can be handled and processed while recording the electrostatic charges on the chrome patterns created by friction or field induction just as a reticle would "see" during normal processing.

Sub-Resolution Assist Features (SRAFs) are typically the smallest features on a photomask and amplify many of the challenges in mask manufacturing. During the initial stages of process development, resist feature adhesion is the dominate damage mechanism. Throughout mask fabrication, the influence of inherent material properties and wet processing can eventually delaminate SRAFs. The various mechanisms that cause SRAF damage will be presented systematically. Process optimization steps to address the failure mechanisms will be presented. Data illustrating the improved process window for small features will be included.

Semiconductor scaling is expected to continue to hp32nm and beyond, accompanied by explosive data volume expansion. Required minimum feature size at hp 32nm will be less than 50nm on the mask, according to ITRS2007⁽¹⁾. EBM 7000 is a newly designed mask writer for the hp32 nm node with an improved electron optical column providing the beam resolution (10 nm measured in situ) and beam current density (200 A/cm²) necessary for cost effective mask production at hp32nm node. In this paper we report on column improvements, the in situ beam blur measurement method and writing results from EBM 7000. Written patterns show dose margin (CD change [nm] / 1 % dose change) of .94 nm /1 % dose for line/space arrays using chemically amplified resist PRL009 and our standard processing. Using a simple model to relate the measured beam intensity distribution to the measured dose margin, we infer an effective total blur of 30 nm, dominated by a contribution of 28 nm from the resist exposure and development process. Further evidence of the dominance of the process contribution is the measured improvement in dose margin to .64 nm/% dose obtained by modifying our standard process. Even larger process improvements will be needed for successful fabrication of hp22nm masks.

In the Mask D2I project at ASET, the authors designed a novel electron beam exposure system using the concepts of MCC (multi column cell), CP (character projection), and VSB (variable shaped beam) to improve the throughput of electron beam exposure systems. They presented outlines of a proof-of-concept system of MCC, and have shown the performances of VSB and CP in the system. They evaluated the impacts on beam position in one column cell caused by deflections in another column cell. The impacts were found to be less than 0.1nm in presence of major deflections in the neighboring column cell. Hence it was concluded that there was no noticeable impact on deflections cause by the neighboring column cells in the MCC system.

Projection Mask-Less Patterning (PMLP) is based on many hundred thousands of ion beams working in parallel. A PMLP proof-of-concept tool has been realized as part of the European project CHARPAN (Charged Particle Nanotech) and has been presented at SPIE Photomask BACUS 2007. Using 10 keV protons, 16nm hp resolution has been demonstrated in non- CAR materials (HSQ) with 25μC/cm² exposure dose. The system is upgraded to a CHARPAN Engineering Tool (CHET) with a laser-interferometer controlled vacuum stage and a CMOS based programmable Aperture Plate System (APS) providing ca. 40,000 beams with < 20nm spot size. The engineering of an ion Mask Exposure Tool (iMET) for the 22nm hp mask node has been started; main iMET features are discussed.

Bimetallic thin-films of Bi/In act as negative thermal resists when laser exposure pulse (7mJ/sq. cm for 4 nsec) converts the film into a transparent eutectic metallic oxide alloy. Resist transparency varies with exposed laser power, changing from <0.1% (3.0 OD) unexposed to >60% (0.22 OD) exposed. This generates direct-write gray scale photomasks, and adding a feedback system where the transparency is measured and adjusts the writing process to account for local variations in the film, achieves >64 gray level control. These resists are also wavelength invariant, operating from visible to EUV with a resolution >42nm after development using a diluted RCA-2 solution (HCl:H₂O₂:H₂0 @ 1:1:48) with a gamma of 2-18. Longer duration exposures with lower instantaneous intensities result in lower gammas, while shorter exposures with higher energies give higher gammas. One limitation on these resists is that the exposure energy must be delivered in a single pulse. This limitation puts pulse energy requirements into the mJ per pulse range: greater than desired for EUV exposure systems. Bimetallic thermal resists remain almost unaffected during a sub-threshold exposure that does not reach the activation energy. It has been shown that the resist and substrate can be heated below the threshold energy, to temperatures of at least 90°C, without creating any exposure of the resist. In this research, Bi/In resists are heated through a range of substrate temperatures, measured for their optical exposure requirements and gammas under these conditions, and used to determine if substrate heating can improve the film's sensitivity.

In double patterning lithography (DPL) layout decomposition for 45nm and below process nodes, two features must be assigned opposite colors (corresponding to different exposures) if their spacing is less than the minimum coloring spacing.^{5, 11, 14} However, there exist pattern configurations for which pattern features separated by less than the minimum coloring spacing cannot be assigned different colors. In such cases, DPL requires that a layout feature be split into two parts. We address this problem using a layout decomposition algorithm that incorporates integer linear programming (ILP), phase conflict detection (PCD), and node-deletion bipartization (NDB) methods. We evaluate our approach on both real-world and artificially generated testcases in 45nm technology. Experimental results show that our proposed layout decomposition method effectively decomposes given layouts to satisfy the key goals of minimized line-ends and maximized overlap margin. There are no design rule violations in the final decomposed layout. While we have previously reported other facets of our research on DPL pattern decomposition,6 the present paper differs from that work in the following key respects: (1) instead of detecting conflict cycles and splitting nodes in conflict cycles to achieve graph bipartization,⁶ we split all nodes of the conflict graph at all feasible dividing points and then formulate a problem of bipartization by ILP, PCD⁸ and NDB⁹ methods; and (2) instead of reporting unresolvable conflict cycles, we report the number of deleted conflict edges to more accurately capture the needed design changes in the experimental results.

Double Process Lithography (DPL) has been widely accepted as a viable printing technique for critical layers at 45nm nodes and below. In addition, DPL technique also allows us to use available process tool-sets with less capability to develop the next node CMOS devices in early research and development stages with additional photo-masks. One practical issue of applying DPL technique is the process crosstalk, which is the impact of the existing etched patterns after the 1st process to the overall lithography performance during the 2nd printing process. In this paper, we evaluated the DPL process for contact holetype patterning with a 193nm silicon-containing bi-layer photo-resist. We explained the bi-layer photoresist process flow and its low process cross-talk characteristics when applied in our DPL process. We also discussed the challenges of printing small contacts in the DPL process. The preliminary experiment results indicated that silicon-containing photo-resist process is a good candidate for DPL process in the contact hole-type of patterns, and it has good characteristics of low process cross-talk. The flexibility of the drydevelop process in bi-layer resist also offered us another way to form small contacts in the substrate film. At the end, we provided some suggestions in contact pattern decomposition algorithm and related exposure-tool alignment strategies for future implementation of DPL technology.

We studied the mask defect printability for both opaque and clear defects in the spacer patterning process. The spacer patterning process consists of the development of photoresist film, the etching of the core film using the photoresist pattern as the etching mask, the deposition of a spacer film on both sides of the core film pattern, and the removal of the core film. The pattern pitch of the spacer film becomes half that of the photoresist. The opaque defect and the clear defect of the mask, respectively, resulted in an "open-short complex" defect and a short defect in the spacer pattern, The defect size of both the opaque and clear defect became smaller as the process proceeded from the development to the core film etching and the spacer pattern fabrication. The decrease of the mask defect printability during the spacer process is likely to be related to the reduction of the line width roughness (LWR) and to the reduction of mask enhanced factor (MEF). The acceptable mask defect size was also studied from the viewpoint of the defect printability to the spacer pattern for both the opaque and clear defect, and found to be 55-60nm, which was relaxed from that in ITRS2007.

For keeping pace with Moore's Law of reducing the feature sizes on integrated circuits, the driving forces have been reductions in the exposure-tool wavelength, and increases in the lens numerical aperture (NA). With extreme ultra-violet (EUV) lithography and 3rd-generation immersion delayed for production use, these driving forces are now stalled at a wavelength of 193 nm and an NA of 1.35. Therefore, double-patterning technology (DPT) is needed for printing 22 nm device node features. With DPT, a 22 nm layout is split into two patterns. Each pattern is printed using 32 nm node lithography technology, and the original pattern is recovered by a logical summation (the Boolean OR operation) of these two separately exposed patterns. DPT presents several challenges for printability verification. First, the etch target can be very different from the resist target because significant biasing is used to improve the lithography process window. Second, overlaps between the two patterns produce new problems such as sharp-cornered pinching at pattern junctions, and bridging between patterns. Finally, there are additional process variations: misalignment between the two patterns, and twice as many dose and defocus dimensions. We present results from a full-chip DPT-verification tool that addresses these challenges. We also provide examples of lithography problems that are specific to DPT, and describe possible guidance for the resolution enhancement techniques (RET) and design tools.

For 32 nm test chips, aggressive resolution enhancement technology (RET) was required for 1x metal layers to enable printing minimum pitches before availability of the final 32 nm exposure tool. Using a currently installed immersion scanner with 1.2 numerical aperture (NA) for early 32 nm test chips, one of the RET strategies capable of resolving the minimum pitch with acceptable process latitude was dipole illumination. To avoid restricting the use of minimum pitch to a single orientation, we developed a double-expose/single-develop process using horizontal and vertical dipole illumination. To enable this RET, we developed algorithms to decompose general layouts, including random logic, interconnect test patterns, and SRAM designs, into two mask layers: a first exposure (E1) of predominantly vertical features, to be patterned with horizontal dipole illumination; and, a second exposure (E2) of predominantly horizontal features, to be patterned with vertical dipole illumination. We wrote this algorithm into our OPC program, which then applies sub-resolution assist features (SRAFs) separately to the E1 and E2 masks, coordinating the two to avoid problems with overlapping exposures. This was followed by two-mask OPC, using E1 and E2 as mask layers and the original layout (single layer) as the target layer. In this paper, we describe some of the issues with decomposing layout by orientation, issues that arise in SRAF application and OPC, and some approaches we examined to address these issues.

Double patterning (DP) technology is one of the main candidates for RET of critical layers at 32nm hp. DP technology is a strong RET technique that must be considered throughout the IC design and post tapeout flows. We present a complete DP technology strategy including a DRC/DFM component, physical synthesis support and mask synthesis. In particular, the methodology contains: - A DRC-like layout DP compliance and design verification functions; - A parameterization scheme that codifies manufacturing knowledge and capability; - Judicious use of physical effect simulation to improve double-patterning quality; - An efficient, high capacity mask synthesis function for post-tapeout processing; - A verification function to determine the correctness and qualify of a DP solution; Double patterning technology requires decomposition of the design to relax the pitch and effectively allows processing with k1 factors smaller than the theoretical Rayleigh limit of 0.25. The traditional DP processes Litho-Etch-Litho- Etch (LELE) [1] requires an additional develop and etch step, which eliminates the resolution degradation which occurs in multiple exposure processed in the same resist layer. The theoretical k₁ for a double-patterning technology applied to a 32nm half-pitch design using a 1.35NA 193nm imaging system is 0.44, whereas the k₁ for a single-patterning of this same design would be 0.22 [2], which is sub-resolution. This paper demonstrates the methods developed at Mentor Graphics for double patterning design compliance and decomposition in an effort to minimize the impact of mask-to-mask registration and process variance. It also demonstrates verification solution implementation in the chip design flow and post-tapeout flow.

A Pixel-based sub-resolution assist feature (SRAF) insertion technique has been considered as one of the promising solutions by maximizing the common process window. However, process window improvement of the pixel-based SRAF technique is limited by the simplification of SRAFs for mask manufacturability. Mask simplification and mask rule check (MRC) constraints parameters for pixel-based SRAF technique are the critical factors for mask production without a big loss of its benefit. In this study, correlation of MRC control was analyzed in terms of the robustness to process variation for a contact layer of 32nm device node. An optimum condition of MRC constraints was selected by balancing the process window and mask manufacturability. In addition, a novel and practical methodology for 32nm device node development was proposed to keep the mask complexity low and to take full advantage of process window improvement using pixel-base SRAF insertion.

The continuing reduction in feature dimensions and tightening of process constraints have led to an increasing demand for model-based approaches, which can efficiently explore the AF solution space, and achieve AF configurations not easily accessible via rules. In this work, we approach the AF placement problem as an inverse imaging problem. We discuss the generation of an inverse mask field and its use in determining the assist feature location. The results are compared with the single iteration intensity-field based AF placement with regard to symmetry, speed, memory, convergence, and accuracy. Several results with different pitches and illumination conditions are presented to demonstrate the robustness and adaptability of the inverse mask AF placement.

Models Based Optical Proximity Correction (MBOPC) is used extensively in the semiconductor industry to achieve robust pattern fidelity in modern lithographic processes. Much of the complexity in OPC algorithms is handled by advanced commercial software packages. These packages give users the ability to set many parameters in the OPC code decks which are used to customize the recipes for specific design styles and manufacturing process settings. Some of the most important parameters in traditional OPC recipes are the fragmentation rules, which determine how edges of polygons are fragmented in a traditional edge-based correction algorithm. It is important to find settings which can deliver good results on a wide variety of complex layout styles. One approach to setting these parameters is through a Design of Experiments (DOE) approach where many different settings are tested in a systematic fashion, in an attempt to find appropriate fragmentation rules for a wide variety of layouts. This is a very straight-forward and powerful technique, but it can be very computationally expensive, particularly as the number of independent variables becomes large. In this paper we examine the usefulness of Genetic Algorithm (GA) optimization techniques for setting the fragmentation parameters. Our work is focused on using GAs to tune parameters rather than on core algorithms used in mask data correction. We use challenging metal layout patterns and optimize fragmentation rules to try to minimize residual edge placement errors, while trying to generate fragmentation that does not result in excessive runtime, or mask manufacturing challenges.

A single patterning solution is still desirable to keep the costs low for high volume wafer manufacturing. This paper will outline the process steps necessary to scale the single patterning approach for gate level from 65mn into the 45nm technology node. They consist mainly of the introduction of a new software for optical proximity correction, the introduction of model based process window correction, the switch to model based etch proximity correction, and support of an ultra dense SRAM cell. All technology requirements could be met with this single patterning solution.

As devices size move toward 90nm technology node or below, defining uniform bit line CD of flash devices is one of the most challenging features to print in KrF lithography. There are two principal difficulties in defining bit line on wafer. One is insufficient process margin besides poor resolution compared with ArF lithography. The other is that asymmetric bit line should be made for OPC(Optical Proximity Correction) modeling. Therefore advanced ArF lithography scanner should be used for define bit line with RETs (Resolution Enhancement Techniques) such as immersion lithography, OPC, PSM(Phase Shift Mask), high NA(Numerical Aperture), OAI(Off-Axis Illumination), SRAF(Sub-resolution Assistant Feature), and mask biasing.. Like this, ArF lithography propose the method of enhancing resolution, however, we must spend an enormous amount of CoC(cost of ownership) to utilize ArF photolithography process than KrF. In this paper, we suggest method to improve of bit line CD uniformity, patterned by KrF lithographic process in 90nm sFlash(stand alone Flash) devices. We applied new scheme of mask manufacturing, which is able to realize 2 different types of mask, binary and phase-shift, into one plate. Finally, we could get the more uniform bit lines and we expect to get more stable properties then before applying this technique.

The identification of OPC induced litho hotspots within the product design is essential and a must to make sure that a new OPC model is working correctly and does no harm to the design and future product. Several techniques and methods for OPC verification and identification of hotspots are known and long adopted within the field. An optical rule check done by the simulation software after OPC is one way of identifying hotspots within the design of the whole chip. This is typically done by using a DRC-type width or space check on simulation contours (nominal exposure contour or process window contours). However, the pass/fail nature of this check at a single CD value requires good calibration of the simulation model to avoid false positives and ease of disposition at tapeout. Another method is the process window qualification method which uses the defect inspection of a focus exposure matrix wafer for OPC hotspot identification. However, this can not be done prior to ordering a mask. Based on a 45nm line space layer OPC qualification, we will demonstrate how optical rule check and process window qualification is performed, what the individual results will be, and how they can be used for OPC quality evaluation. The general goal of this work is to show the capabilities of optical rule check and process window qualification, compare both methods, and detect limitations.

Current flash memory technology is facing more and more challenges for 45nm and 32nm node technology. To get good CD and yield control, optimized RET, OPC modeling and DFM techniques have to be applied [1]. To enhance process window (PW) and better CD control for main features, assist features (SB) have to be used. Simulation and wafer evaluation show that the SB CD performance is very critical. Based on OPC simulation, we can get a very good prediction about the CD size and placement of assist features. However, we can not always get what we want from mask suppliers. For 45nm node technology and beyond, The SB CD size (~ 20nm at 1X) has almost pushed to the current mask process limit. Wafer fabs have a very big concern about the stability of linearity signatures from different suppliers and different products in order to keep high accuracy of OPC models. Actually the CD linearity signature varies from one mask supplier to another and also varies from product to product. To improve the SB CD control, the ideal goal is to make "flat" linearity for all mask suppliers. By working closely with TPI mask supplier, we come up solutions to improve SB CD control to get "flat" linearity. Also technology development is causing more severe SB printability, we proposed a methodology to use AIMS for predicting SB printability. Wafer results proved the feasibility for these methodologies.

The use of MegaSonic energy is widely accepted in photomask cleaning. For the advanced technology nodes, beyond 65nm, the problem of damaged sub resolution assist features (SRAF) becomes highly prevalent. Such feature damages are often related to the application of MegaSonic energy. We investigated the influence of common cleaning media and MegaSonic parameters for damaging SRAF patterns. A special option of our cleaning tool was utilized to test a large number of different settings with low resources for test mask and defect inspections. In this paper we will present the results of our investigations and present conditions for MegaSonic cleaning which will enable the wide use of this technology beyond the 45nm technology node.

Particle removal without damage has been demonstrated for <60nm photomask sub-resolution assist features with droplet momentum cleaning technology that employs NanoDroplet^TM mixed-fluid jet nozzle. Although 99%+ particle removal efficiency can be achieved for standard Si₃N₄ particles with broad size distribution, there are some cleaning challenges with small (<100nm) and large contact area (>500nm) particles. It was found that tunable uniform cavitation can provide the additional physical assist force needed to improve cleaning efficiency of these challenging particles while meeting the damage-fee cleaning requirement. An integrated cleaning process was developed that combines both droplet momentum and damage-free cavitation technology. Cleaning tests were performed with different types of challenging particles. The results showed 5-8% particle removal efficiency improvement as compared to momentum based only cleaning. All masks were processed using the Tetra^TM mask cleaning tool configured with NanoDroplet^TM mixed fluid jet technology and full face megasonics.

The continuous evolution of LSI design rules has created an increased demand for the use of KrF and ArF phase-shift photomasks (EPSMs). One of the critical issues in the use of those photomasks, especially ArF half-tone photomasks, has been the generation of optical hazes known as (NH4)2SO4. The other critical issue has been a relatively large phase shift of those ArF and KrF photomasks caused by so-called haze-free mask cleaning.. In the present study we used an SPM integrated clean (as a reference) consisting of heated SPM, diluted SC-1 and heated UPW (widely known for rinsing), and a haze-free integrated mask clean consisting of Ozonated-water with a simultaneous 222nm Excimer UV irradiation, diluted SC-1 and heated UPW. We found that both Ozonated-water with a simultaneous 222nm Excimer UV irradiation and the diluted SC-1 (the components of the haze-free integrated clean) caused a sizable phase shift during the mask clean. We also found that the other component of the haze-free integrated clean, the heated UPW developed a relatively large phase shift in those photomasks. We have confirmed that the more we repeat the use of the 172nm Excimer UV light irradiation treatment before the clean, the less (more improved) phase shift has been realized in the haze-free clean. We found that the haze-free integrated clean also developed the CD shifts of the above photomasks and that those CD shifts could be recovered (reduced) drastically by the use of the 172nm Excimer UV light irradiation before the clean.

In advanced IC manufacturing reticle contamination through crystal growth causing printed defects¹ is a major source of yield loss. This crystal growth requires frequent inspection to ensure reticles are free from such contamination (reticle requalification). STARlight is the industry accepted method for mask inspection in wafer fabs for reticle re-qualification (requal) ². The principal focus of this paper is a study correlating the detection of contamination (crystal growth) on logic product masks found with STARlight to defects that can be found on a print-check wafer (a photo-resist test wafer). A critical component in this study was the translation of reticle coordinates to wafer coordinates and integrating the results between high-resolution broadband DUV BrightField inspection (BF) and scanning electron microscope (SEM) review. All of the STARlight defect locations were reviewed using the SEM regardless if the defect was found on opaque or on clear surfaces of the mask. As such defects being SEM reviewed were classified as either 'printing', 'early-warning' or 'non-printing'. BF defect inspection results after repeater analysis were compared with STARlight results to determine the correlations. SEM Defect Review was performed on STARlight inspection results and the resulting classified data was correlated to the BF defect inspection results.

We have investigated the factors having influence on the lithographic fidelity variation in 193nm masks. Significant researches have been studied that haze contamination, resulting from the absorption of chemical residual ions and mask container out-gassing in mask fabrication, is one of the major component to reduce the optimized lithography condition such as Best Focus, Depth of Focus and Exposure latitude of individual feature. And also environment being containing humidity, ambient AMC (airborne molecular contamination) react with high exposure energy to form crystal growth of ionic molecular complex such as ammonium sulfate causing abnormal printability. Moreover, optical issue of organic pellicle membrane is thoroughly considered that perfluoro polymer degradation induced by high photon energy affect the transmittance intensity. Consequently, these photophysical alterations bring about the lithographic variation and cause considerable defects in wafer printing. In this paper, we tried to verify the influence grade inducing the lithographic variation among the latent contamination factors consisting of mask back-side quartz contamination, the growth of exposure energy based haze phenomena, thin organic pellicle membrane degradation and modified character of MoSiN surface. Metrological inspection and photochemical reaction evaluations were conducted with several equipments including AIMS, Scatterometer, XPS, SIMS, FT-IR, UV, ArF acceleration laser to demonstrate the proposal mechanism of correlation between lithographic variation and latent contamination factors. The optical issues and lifetime of ArF PSM were simulated with the evaluation of effects of pellicle degradation and surface modification.

In this paper, we expand on our earlier work^1,2 reporting the use of high sensitivity DUV transmission metrology as a means for detection of progressive transmission loss on mask and pellicle surfaces. We also report a use case for incoming reticle qualification based on DUV transmission uniformity. Traditional inspection systems rely on algorithms to locate discrete defects greater than a threshold size (typically > 100nm), or printing a wafer and then looking for repeating defects using wafer inspection and SEM review. These types of defect inspection do not have the ability to detect transmission degradation at the low levels where it begins to impact yield. There are numerous mechanisms for transmission degradation, including haze in its early, thin film form, electric-field induced field migration, and pellicle degradation. During the early development of haze, it behaves as a surface film which reduces 193nm transmission and requires compensation by scanner dose. The film forms in a non-uniform fashion, resulting from non-uniformity of exposure on the pattern side due to varying dose passing through the attenuating layers. As this non-uniformity evolves, there is a gradual loss of wafer critical dimension uniformity (CDU) due to a degradation of the exposure dose homogeneity. Electric-field induced migration also appears to manifest as a non-uniform transmission loss, typically presenting with a radial signature. In this paper we present evidence that a DUV transmission measurement system, Galile^TM, is capable of detecting low levels of transmission loss, prior to CDU related yield loss or the appearance of printing defects. Galileo is an advanced DUV transmission metrology system which utilizes a wide-band, incoherent light source and non-imaging optics to achieve sensitivities to transmission changes of less than 0.1%. Due to its very high SNR, it has a fast MAM time of less than 1 sec per point, measuring a full field mask in as little as 30 minutes. A flexible user interface enables users to easily define measurement recipes, threshold sensitivities, and time-based tracking of transmission degradation. The system measures through pellicle under better than class 1 clean air conditions.

Haze issues are getting more serious since size of Haze defect printable on the water surface that could matter is decreasing further with reduced pattern size. Many efforts have been made to reduce the contamination level on the photomask surface by applying wet or dry processes. We have successfully reduced surface contamination down to subppb level for organic and inorganic chemicals. No matter how well the mask surface is cleaned, chemical contaminant cannot be perfectly eliminated from the surface. As long as contaminants exist on the surface, they are getting aggregated around certain points with higher energy to create defects on it during laser exposure. Also, the cleaned mask surface could be contaminated again during following processes such as shipping and storage. Here, we propose a new paradigm for Haze retardation where we severely decelerate defect generation and growth rather than eliminate chemical contaminants on the mask surface. We have made mask surface on which chemical contaminants are hardly accumulated to generate Haze defects even during laser exposure. By creating mask surface insensitive to chemical impurity level up to a certain degree, we are able to retard Haze occurrence much better than by reducing surface impurities down to sub-ppb level. This approach has another advantage of allowing a freedom for mask environment during the process of shipping, storage, and exposure. We further investigate how the treated mask surface should have strong resistance against chemical contaminant aggregation towards Haze defect generation around specific points with high energy.

Backside defects a few micrometers in size are serious concern in lithography because they can degrade the image quality on a wafer. It was known that defects attached on the backside affected the printing images on a wafer by locally altering the partial coherence (σ) and the transmitted intensity of the illumination. The ability to detect and to simulate their impact of defects on the backside is one of the key components in ensuring quality of photomask. The purpose of this study is to determine the minimum size of defects on the backside which would be affected printability in 193nm photolithography. It was investigated to the influence of wafer critical dimension (CD) variation according to illumination and NA, that of refraction according to defect size. For this study, a reticle was designed to include line and space patterns, contact patterns and isolated patterns on the front side. And the type of defects attached on the backside was made of chrome to investigate the relation between transmittance of backside defects and its printability. The correlation of measurements made with UV and DUV-based inspection system; simulation performed with a 193nm aerial image measurement system. Besides the allowable size of backside defects was determined using the criterion of a maximum intensity variation of 10%.

Traditionally, definition of mask specifications is done completely by the mask user, while characterization of the mask relative to the specifications is done completely by the mask maker. As the challenges of low-k1 imaging continue to grow in scope of designs and in absolute complexity, the inevitable partnership between wafer lithographers and mask makers has strengthened as well. This is reflected in the jointly owned mask facilities and device manufacturers' continued maintenance of fully captive mask shops which foster the closer mask-litho relationships. However, while some device manufacturers have leveraged this to optimize mask specifications before the mask is built and, therefore, improve mask yield and cost, the opportunity for post-fabrication partnering on mask characterization is more apparent and compelling. The Advanced Mask Technology Center (AMTC) has been investigating the concept of assessing how a mask images, rather than the mask's physical attributes, as a technically superior and lower-cost method to characterize a mask. The idea of printing a mask under its intended imaging conditions, then characterizing the imaged wafer as a surrogate for traditional mask inspections and measurements represents the ultimate method to characterize a mask's performance, which is most meaningful to the user. Surrogate wafer print (SWaP) is already done as part of leading-edge wafer fab mask qualification to validate defect and dimensional performance. In the past, the prospect of executing this concept has generally been summarily discarded as technically untenable and logistically intractable. The AMTC published a paper at BACUS 2007 successfully demonstrating the performance of SWaP for the characterization of defects as an alternative to traditional mask inspection [1]. It showed that this concept is not only feasible, but, in some cases, desirable. This paper expands on last year's work at AMTC to assess the full implementation of SWaP as an enhancement to mask characterization quality including defectivity, dimensional control, pattern fidelity, and in-plane distortion. We present a thorough analysis of both the technical and logistical challenges coupled with an objective view of the advantages and disadvantages from both the technical and financial perspectives. The analysis and model used by the AMTC will serve to provoke other mask shops to prepare their own analyses then consider this new paradigm for mask characterization and qualification.

High Resolution reticle inspection is well-established as a proven, effective, and efficient means of detecting yieldlimiting mask defects as well as defects which are not immediately yield-limiting yet can enable manufacturing process improvements. Historically, RAPID products have enabled detection of both classes of these defects. The newlydeveloped Wafer Plane Inspection (WPI) detector technology meets the needs of some advanced mask manufacturers to identify the lithographically-significant defects while ignoring the other non-lithographically-significant defects. Wafer Plane Inspection accomplishes this goal by performing defect detection based on a modeled image of how the mask features would actually print in the photoresist. This has the effect of reducing sensitivity to non-printing defects while enabling higher sensitivity focused in high MEEF areas where small reticle defects still yield significant printing defects on wafers. This approach has several important features. The ability to ignore non-printing defects and to apply additional effective sensitivity in high MEEF areas enables advanced node development. In addition, the modeling allows the inclusion of important polarization effects that occur in the resist for high NA operation. This allows for the results to better match wafer print results compared to alternate approaches. Finally, the simulation easily allows for the application of arbitrary illumination profiles. With this approach, users of WPI can make use of unique or custom scanner illumination profiles. This allows the more precise modeling of profiles without inspection system hardware modification or loss of company intellectual property. A previous paper [1] introduced WPI in D:D mode. This paper examines the operation and results for WPI in Die:Database mode.

Wafer Plane Inspection (WPI) is a novel approach to inspection, developed to enable high inspectability on fragmented mask features at the optimal defect sensitivity. It builds on well-established high resolution inspection capabilities to complement existing manufacturing methods. The production of defect-free photomasks is practical today only because of informed decisions on the impact of defects identified. The defect size, location and its measured printing impact can dictate that a mask is perfectly good for lithographic purposes. This inspection - verification - repair loop is timeconsuming and is predicated on the fact that detectable photomask defects do not always resolve or matter on wafer. This paper will introduce and evaluate an alternative approach that moves the mask inspection to the wafer plane. WPI uses a high NA inspection of the mask to construct a physical mask model. This mask model is used to create the mask image in the wafer plane. Finally, a threshold model is applied to enhance sensitivity to printing defects. WPI essentially eliminates the non-printing inspection stops and relaxes some of the pattern restrictions currently placed on incoming photomask designs. This paper outlines the WPI technology and explores its application to patterns and substrates representative of 32nm designs. The implications of deploying Wafer Plane Inspection will be discussed.

Wafer Plane Inspection (WPI) is an inspection mode on the KLA-Tencor TeraSca^TM platform that uses the high signalto- noise ratio images from the high numerical aperture microscope, and then models the entire lithographic process to enable defect detection on the wafer plane[1]. This technology meets the needs of some advanced mask manufacturers to identify the lithographically-significant defects while ignoring the other non-lithographically-significant defects. WPI accomplishes this goal by performing defect detection based on a modeled image of how the mask features would actually print in the photoresist. There are several advantages to this approach: (1) the high fidelity of the images provide a sensitivity advantage over competing approaches; (2) the ability to perform defect detection on the wafer plane allows one to only see those defects that have a printing impact on the wafer; (3) the use of modeling on the lithographic portion of the flow enables unprecedented flexibility to support arbitrary illumination profiles, process-window inspection in unit time, and combination modes to find both printing and non-printing defects. WPI is proving to be a valuable addition to the KLA-Tencor detection algorithm suite. The modeling portion of WPI uses a single resist threshold as the final step in the processing. This has been shown to be adequate on several advanced customer layers, but is not ideal for all layers. Actual resist chemistry has complicated processes including acid and base-diffusion and quench that are not consistently well-modeled with a single resist threshold. We have considered the use of an advanced resist model for WPI, but rejected it because the burdensome requirements for the calibration of the model were not practical for reticle inspection. This paper describes an alternative approach that allows for a "soft" resist threshold to be applied that provides a more robust solution for the most challenging processes. This approach is just finishing beta testing with a customer developing advanced node designs.

The AIM^TM45-193i is the established tool for mask performance qualification and defect printing analysis in the mask shop under scanner conditions. Vector effects are taken into account by the proprietary Zeiss vector effect emulator. In several studies an excellent correlation to wafer prints has been reported. However, a systematic offset to wafer prints in terms of mask error enhancement factor (MEEF) and exposure latitude has been observed which is attributed to well known resist effects. The AIMS^TM measures the aerial image in resist whereas in a real lithography process further image blur of the latent image is caused by photo acid diffusion during wafer processing and resist development. To explain the gap between the AIM^TM and wafer prints we have investigated aerial images in combination with an easy to use resist model. It does take resist effects into account with sufficient accuracy to explain printing behavior of photo masks but without the need to calibrate lots of parameters of the actually used resist which usually are not known to a mask shop. The resist effects predominantly reduce the image contrast and thus increase the MEEF and the sensitivity to mask defects. This somewhat counterintuitive behavior is labeled "contrast enhancement by contrast reduction". Additionally application of the resist model improves the agreement of e.g. the exposure latitude or MEEF measured by the AIMS^TM compared to wafer prints.

The AIMS^TM-45, when used in scanner mode, can emulate image intensity as seen in resist on the wafer at scanner illumination conditions. We show that this feature makes AIMS^TM-45 well-suited to analyze patterns treated with inverse lithography. We have used an inverse lithography technique by Mentor Graphics, to treat a random contact hole layout (drawn at minimal pitch 115nm) for imaging at NA 1.35. The combination of the dense 115nm pitch and available NA of 1.35 makes Quasar illumination necessary, and the inverse lithography treatment automatically generated optimal (model-based) Assist Features (AF) for all geometries in the design. The mask, after inverse lithography treatment, has CH patterns with numerous AF of different sizes and orientations, and is a challenge for both mask making and mask qualification. We have analyzed the inverse lithography masks with the model-based AF using an AIMS^TM-45 aerial image measurement tool, and compare the results of the AIMS^TM-45 to wafer data obtained after exposure on an ASML XT:1900i. A first benefit of AIM^TM-45 is that the most meaningful quantity (image in resist) is generated without the intermediate steps of doing multiple reticle SEM measurements followed by extensive simulation. A second point of interest is that the AIMS^TM-45 generates image intensities, which allows a direct validation of the intensity-driven inverse litho conversion. Both features prove the value of the AIMS^TM-45 for analyzing inverse litho masks and geometries.

Mask defect disposition gets more difficult and time-consuming with each progressive lithography node. Mask inspection tools commonly use 250 nm wavelength, giving resolution of 180 nm, so critical defect sizes are far less than the optical resolution - too small for defect analysis. Thus the rate of false or nuisance defect detection is increasing rapidly and analysis of detected defects is increasingly difficult. As to judging the wafer printability of defects, AIMS (Aerial Image Measurement System) tools are commonly used but are also time-consuming if defect count is high. For improving the efficiency of mask defect disposition, we propose the combination of a SEM defect review tool and defect disposition and simulation software, which use high-resolution SEM images of defects to do defect review, defect disposition, and wafer printing simulation of defects automatically or manually. The SEM defect review tool, DIS-05 developed by Holon Co. Ltd., is designed for defect review and disposition using reference images derived from e-beam files or CAD database. This tool uses the Automated Defect Analysis Software (ADAS) developed from AVI LLC. to interface the inspection tool and the DIS-05. ADAS detects false defects before SEM imaging and performs aerial image simulation from the SEM and CAD images to estimate the wafer CD error caused by each defect. We report on its speed (>300 defects/hour), classification accuracy and simulation accuracy when used with masks at the 45 nm technology node and beyond. This combination of SEM and ADAS is expected to significantly accelerate process development and production for the 45 and 32 nm nodes. It will also increase the masksper- day throughput of inspection and AIMS tools by shifting most defect review to ADAS software using SEM images. At preliminary tests showed the combination tool can do auto defect disposition and simulation with promising results.

Conventional photomask inspection techniques utilize global sensitivity for all inspected area in the die; SRAF and OPC features become the sensitivity-limiters, which can result in reduced visibility to defects of interest (DOI). We describe the implementation of Sensitivity Control Layer (SCL), a novel database inspection methodology for the KLA-Tencor TerascanHR platform. This methodology enables inspection at maximum sensitivity in critical die-areas via "layer definition" during job set-up and sensitivity management of the layers during inspection. Memory device inspection performance was improved through the use of up to six control layers to increase sensitivity in the active area while reducing nuisance detections by as much as 100X. The corresponding inspection time was reduced by 30%, illustrating the potential for substantial throughput advantage using SCL. Post-inspection analysis and improved disposition accuracy of the SCL-enabled inspections will also benefit cycle time and higher throughput. In all test cases, sensitivity parameters were increased in the regions of interest over baseline inspections run with typical production-use methodologies. SCL inspection management and application on OPC structures, SRAFs, and MRC violations (slivers) are discussed in detail.

Programmed defect test masks serve the useful purpose of evaluating inspection system sensitivity and capability. It is widely recognized that when evaluating inspection system capability, it is important to understand the actual sensitivity of the inspection system in production; yet unfortunately we have observed that many test masks are a more accurate judge of theoretical sensitivity rather than real-world usable capability. Use of ineffective test masks leave the purchaser of inspection equipment open to the risks of over-estimating the capability of their inspection solution and overspecifying defect sensitivity to their customers. This can result in catastrophic yield loss for device makers. In this paper we examine some of the lithography-related technology advances which place an increasing burden on mask inspection complexity, such as MEEF, defect printability estimation, aggressive OPC, double patterning, and OPC jogs. We evaluate the key inspection system component contributors to successful mask inspection, including what can "go wrong" with these components. We designed and fabricated a test mask which both (a) more faithfully represents actual production use cases; and (b) stresses the key components of the inspection system. This mask's patterns represent 32nm, 36nm, and 45nm logic and memory technology including metal and poly like background patterns with programmed defects. This test mask takes into consideration requirements of advanced lithography, such as MEEF, defect printability, assist features, nearly-repetitive patterns, and data preparation. This mask uses patterns representative of 32nm, 36nm, and 45nm logic, flash, and DRAM technology. It is specifically designed to have metal and poly like background patterns with programmed defects. The mask is complex tritone and was designed for annular immersion lithography.

Improvements in repair process, software, and AFM tip technology have brought about an overall 2D shape reconstruction capability to nanomachining that has not been previously imagined. Repair results are shown for various processes to highlight their relative strengths and weaknesses. The impact of technical improvements is shown in the advances in repair dimensional precision and overall imaging performance. The greater technical potential of nanomachining is realized in this examination for mask repair scaled to smaller repair geometries while repairing larger defects that may span these critical patterns.

It has been found that the femtosecond DUV laser mask repair tool has significant utility in the repair of unknown foreign material (FM) contamination of sizes ranging from 50 nm to 30 μm with highly variable z-heights both isolated and within critical complex patterns. Another significant ROI is the repair of masks which have already been pelliclized (through pellicle repair or TPR) where the laser repair tool may work in conjunction with existing through-pellicle inspection hardware to detect and remove FM and correct pattern errors. The capability of the tool is also explored for repairs in patterns including the 45 nm technology node.

The cost and time associated with the production of photolithographic masks continues to grow, driven by the ever decreasing feature size, advanced mask technologies and complex resolution enhancing techniques. Thus employment of a high-resolution, comprehensive mask repair tool becomes a key element for a successful production line. The MeRiT® utilizes electron beam induced chemistry to repair both clear and opaque defects on a variety of masks and materials with the highest available resolution and edge placement precision. This paper describes the benefits of the electron beam induced technique as employed by the MeRiT® system for a production environment.

As optical lithography advances into the 45nm technology node and beyond, new manufacturing-aware design requirements have emerged. We address layout design for interference-assisted lithography (IAL), a double exposure method that combines maskless interference lithography (IL) and projection lithography (PL); cf. hybrid optical maskless lithography (HOMA) in [2] and [3]. Since IL can generate dense but regular pitch patterns, a key challenge to deployment of IAL is the conversion of existing designs to regular-linewidth, regular-pitch layouts. In this paper, we propose new 1-D regular pitch SRAM bitcell layouts which are amenable to IAL. We evaluate the feasibility of our bitcell designs via lithography simulations and circuit simulations, and confirm that the proposed bitcells can be successfully printed by IAL and that their electrical characteristics are comparable to those of existing bitcells.

As the process of migration of Optical process correction (OPC) recipes continues to go from sparse to dense computations, a run time effectiveness issue persists to remain for huge structures that exist in some metal and active layers designs. Even for 45 and 32 nm technology nodes, some polygons might be several microns in width consuming a vast amount of simulation time and order of magnitudes more than sparse simulations to converge. Practically, this problem is pronounced, which is usually the case, when the design comprises these huge structures and other small critical ones that needs many iterations and careful tuning to converge. And thus, a considerable amount of run time will be wasted while applying these sophisticated recipes on big structures that could originally converge within few iterations using a simple recipe. In this context, a convergence-based dense OPC recipe is proposed to deal with designs that have both types of structures. The basic idea is to check convergence prior starting next iteration and skip the rest of the iterations if the whole simulated frame has converged within a predefined tolerance. Also, a reasonable way to define tolerances is explored.

Foundry companies encounter again and again the same or similar lithography unfriendly patterns (Hot-spots) in different designs within the same technology node and across different technology nodes, which eluded design rule check (DRC), but detected again and again in OPC verification step. Since Model-based OPC tool applies OPC on whole-chip design basis, individual hot-spot patterns are treated same as the rest of design patterns, regardless of its severity. We have developed a methodology to detect those frequently appeared hot-spots in pre-OPC design, as well as post OPC designs to separate them from the rest of designs, which provide the opportunity to treat them differently in early OPC flow. The methodology utilizes the combination of rule based and pattern based detection algorithms. Some hotspot patterns can be detected using rule-based algorithm, which offer the flexibility of detecting similar patterns within pre-defined ranges. However, not all patterns can be detected (or defined) by rules. Thus, a pattern-based approach is developed using defect pattern library concept. The GDS/OASIS format hot-spot patterns can be saved into a defect pattern library. Fast pattern matching algorithm is used to detect hot-spot patterns in a design using the library as a pattern template database. Even though the pattern matching approach lacks the flexibility to detect patterns' similarity, but it has the capability to detect any patterns as long as a template exists. The pattern-matching algorithm can be either exact match or a fuzzy match. The rule based and pattern based hot-spot pattern detection algorithms complement each other and offer both speed and flexibility in hot spot pattern detection in pre-OPC and post-OPC designs. In this paper, we will demonstrate the methodology in our OPC flow and the benefits of such methodology application in production environment for 90nm designs. After the hot spot pattern detection, examples of special treatment to selected hot spot patterns will be shown.

OPC model calibration requires thousands of experimental data points. These are then used to calibrate an OPC model. Today, the majority of these steps are performed manually. Metrology for example involves taking the CD-SEM offline for an operator to program it. Considerable time savings is possible by writing the CD-SEM recipe offline. Experimental data preparation is also often performed manually. Manual review of thousands of data points is a tedious task prone to human errors. Here again, automation can greatly alleviate the engineering effort, reduce cycle-time and improve data quality. Data quality improvement alone has been shown to have a significant benefit to model calibration accuracy and predictability. In this paper we present an automated solution for the currently engineering effort intensive components of the OPC model calibration flow. The flow we present is integrated inside the OPC environment. We suggest best practices identified through the implementation of an automated flow, and discuss benefits. Our results demonstrate the capability and quantify the benefits which automation brings in human effort, reduced time to accurate model and improved model quality.

Performing model-based optical proximity correction (MBOPC) on layouts has become an integral part of patterning advanced integrated circuits. Earlier technologies used sparse OPC, the run times of which explode when the density of layouts increases. With the move to 45 nm technology node, this increase in run time has resulted in a shift to dense simulation OPC, which is pixel-based. The dense approach becomes more efficient at 45nm technology node and beyond. New OPC model forms can be used with the dense simulation OPC engine, providing the greater accuracy required by smaller technology nodes. Parameters in the optical model have to be optimized to achieve the required accuracy. Dense OPC uses a resist model with a different set of parameters than sparse OPC. The default search ranges used in the optimization of these resist parameters do not always result in the best accuracy. However, it is possible to improve the accuracy of the resist models by understanding the restrictions placed on the search ranges of the physical parameters during optimization. This paper will present results showing the correlation between accuracy of the models and some of these optical and resist parameters. The results will show that better optimization can improve the model fitness of features in both the calibration and verification set.

In this study, we discuss modeling finite laser bandwidth for application to optical proximity modeling and correction. We discuss the accuracy of commonly-used approximations to the laser spectrum shape, namely the modified Lorentzian and Gaussian forms compared to using measurement-derived laser fingerprints. In this work, we show that the use of the common analytic functions can induce edge placement errors of several nanometers compared to the measured data and therefore do not offer significant improvement compared to the monochromatic assumption. On the other hand, the highlyaccurate laser spectrum data can be reduced to a manageable number of samples and still result in sub 0.5nm error through pitch and focus compared to measured spectra. We have previously demonstrated that a 23-point approximation to the laser data can be generated from the spectrometry data, which results in less than 0.1nm RMS error even over varied illumination settings. We investigate the further reduction in number of spectral samples down to five points and consider the resulting accuracy and model-robustness tradeoffs. We also extend our analysis as a function of numerical aperture and illumination setting to quantify the model robustness of the physical approximations. Given that adding information about the laser spectrum would primarily impact the model-generation run-times and not the run-times for the OPC implementation, these techniques should be straightforward to integrate with current full-chip OPC flows. Finally, we compare the relative performance of a monochromatic model, a 5-point laser-spectral fingerprint, and two Modified Lorentzian fits in a commercial OPC simulator for a 32nm logic lithography process. The model performance is compared at nominal process settings as well as through dose, focus and mask bias. Our conclusions point to the direction for integration of this approach within the framework of existing EDA tools and flows for OPC model generation and process-variability verification.

We have developed an interface which allows to perform rigorous electromagnetic field (EMF) simulations with the simulator JCMsuite and subsequent aerial imaging and resist simulations with the simulator Dr.LiTHO.With the combined tools we investigate the convergence of near-field and far-field results for different DUV masks. We also benchmark results obtained with the waveguide-method EMF solver included in Dr.LiTHO and with the finite-element-method EMF solver JCMsuite. We demonstrate results on convergence for dense and isolated hole arrays, for masks including diagonal structures, and for a large 3D mask pattern of lateral size 10 microns by 10 microns.

Subgrid and subcell FDTD (S-FDTD) methods are described. They can be used for the fast and accurate simulation of mask electromagnetic effects in sub-45nm lithography. The accuracies of the S-FDTD methods are verified by comparison with FDTD and with a very accurate pseudospectral reference solution. The S-FDTD methods are an order of magnitude or more faster than FDTD. Furthermore, the S-FDTD methods require much less memory than FDTD for time marching. Hence, much larger mask areas can be simulated with S-FDTD than with FDTD.

Model Based Optical Proximity Correction (MBOPC) is since a decade a widely used technique that permits to achieve resolutions on silicon layout smaller than the wave-length which is used in commercially-available photolithography tools. This is an important point, because masks dimensions are continuously shrinking. As for the current masks, several billions of segments have to be moved, and also, several iterations are needed to reach convergence. Therefore, fast and accurate algorithms are mandatory to perform OPC on a mask in a reasonably short time for industrial purposes. As imaging with an optical lithography system is similar to microscopy, the theory used in MBOPC is drawn from the works originally conducted for the theory of microscopy. Fourier Optics was first developed by Abbe to describe the image formed by a microscope and is often referred to as Abbe formulation. This is one of the best methods for optimizing illumination and is used in most of the commercially available lithography simulation packages. Hopkins method, developed later in 1951, is the best method for mask optimization. Consequently, Hopkins formulation, widely used for partially coherent illumination, and thus for lithography, is present in most of the commercially available OPC tools. This formulation has the advantage of a four-way transmission function independent of the mask layout. The values of this function, called Transfer Cross Coefficients (TCC), describe the illumination and projection pupils. Commonly-used algorithms, involving TCC of Hopkins formulation to compute aerial images during MBOPC treatment, are based on TCC decomposition into its eigenvectors using matricization and the well-known Singular Value Decomposition (SVD) tool. These techniques that use numerical approximation and empirical determination of the number of eigenvectors taken into account, could not match reality and lead to an information loss. They also remain highly runtime consuming. We propose an original technique, inspired from tensor signal processing tools. Our aim is to improve the simulation results and to obtain a faster algorithm runtime. We consider multiway array called tensor data T CC. Then, in order to compute an aerial image, we develop a lower-rank tensor approximation algorithm based on the signal subspaces. For this purpose, we propose to replace SVD by the Higher Order SVD to compute the eigenvectors associated with the different modes of TCC. Finally, we propose a new criterion to estimate the optimal number of leading eigenvectors required to obtain a good approximation while ensuring a low information loss. Numerical results we present show that our proposed approach is a fast and accurate for computing aerial images.

The usage of conventional OPC models traditionally was confined to the specific process conditions at which the models were. Separable models for computational lithography (CL), including OPC and post-OPC layout verification, allow extrapolation of the calibrated model and accurate prediction at process conditions different from the exact settings used for model calibration. This capability enables significantly reduced turnaround time in early process development, and it opens the way for new applications such as model based process optimization. It relies on sufficiently accurate modeling of litho process components as separate subsystems, in particular mask, scanner optics, and resist process. Inclusion of actual machine parameters of the exposure tool in the optical model can improve model accuracy and predictability, while 'actual machine parameters' may represent either a specific scanner type or an individual exposure tool. We study the impact of machine parameters that can be incorporated in a modern computational litho model, by analyzing their relative effect on predicted CD measurements and extract a ranking in terms of their expected benefit for model separability. An experimental study demonstrates improved model accuracy and separability by inclusion of either scanner-type specific model data or individual machine-specific metrology data in the CL model building process.

Mask Error Enhancement Factor (MEEF) plays an increasingly important role in the DFM and RET flow required to continue shrinking designs in the low-k1 lithography regime. The ability to model and minimize MEEF during lithography optimization and RET application is essential to obtain a usable process window (PW). In Inverse Lithography Technology (ILT), MEEF can be included in the cost function as a nonlinear factor, so that the inversion minimizes MEEF, in addition to optimizing PW and edge placement error (EPE). ILT has been shown to optimize masks for a given source. Using ILT for contemporaneous Source and Mask co-Optimization (SMO) can provide further benefit by balancing the complexity of mask and source. Results demonstrating the benefits of "MEEF-aware" ILT and SMO for advanced technology nodes are presented in this paper.

A modification has been made to the fast simulator RADICAL which allows it to simulate the reflected field from an EUV mask with a buried defect 15,000 times faster than the finite difference time domain method (FDTD). This new version uses an advanced single surface approximation (SSA) instead of ray tracing to model the defective multilayer stack. RADICAL with SSA can simulate a 32nm line space pattern with a buried defect in 4.0s. The accuracy of this method is verified with comparisons to FDTD simulations and good agreement is shown. The ability of this method to simulate large layouts with arbitrary defects is demonstrated. A 1.5μm x 1.5μm layout with an arbitrary buried defect and multilayer surface roughness is simulated in 75s. An alternative algebraic fast model for buried defects near absorber lines is also investigated based on the linear relationship between the surface height of isolated buried defects and the aerial image dip strength. However, the interaction is shown to be too complicated for accurate representation with the model proposed.

Source and mask optimization has become a promising technique to push the limits of 193 nm immersion lithography. As the introduction of EUV lithography is at least delayed to the 22 nm technology node, sophisticated resolution enhancement techniques will already be required at a very early stage. Thus, pinpointing ideal mask layouts, mask materials, and illumination settings are as important aspects for EUV as for optical lithography. In this paper, we propose the application of global optimization techniques to identify appropriate process conditions for EUV lithography, using rigorous mask and imaging simulations.

Design-for-manufacturing (DFM) is becoming an actual design practice among IC manufacturers, designers and EDA companies. Layout assessment by design-rule-check (DRC) using EDA tools is a common practice today to ensure well-manufactured design geometries. Standalone DFM tools, which require iteration loops of DFM analysis and fixing, do not fit well in design flows and are considered cumbersome. A better layout assessment method for DFM issues is required: one that gives actionable feedback, and that can be used with automatic optimization in early design stages. The latter is needed to avoid costly design re-spins that will consume critical time-to-market as well as use a lot of engineering resources, reticles and wafer material costs. For example, a DFM checking tool may report the hotspot types and locations, but this information is not sufficient for designers to decide tradeoffs between different fixing choices and to take care of trade-off between physical and electrical design constraints at the same time. When model-based properties are introduced such as lithographic contour, the tradeoffs between rule-based and model-based properties can only be resolved by the automatic and concurrent optimization. This work demonstrates a methodology of DFM scoring of layout based on preferred rules compliance, lithography GATE printability, as well as the layout fixing. The electrical impact on gates is analyzed and showed reduced variability (compared to nominal behavior) in gate performance. Designers can get visual feedback of the layout quality, as well as improvement suggestions. Takumi TKE software is used to demonstrate automatic and concurrent optimization. The method applies to both cell-level and custom designs.

As the feature size of LSI shrinks the cost of mask manufacturing and turn-around-time (TAT) continues to increase. These increases are reaching to points of great concerns. Association of Super-Advanced Electronics Technologies (ASET) Mask Design, Drawing, and Inspection Technology Research Department (Mask D2I) launched a 4-year program for reducing mask manufacturing cost and TAT by concurrent optimization of MDP, mask writing, and mask inspection that involves exploitation of close relationships and synergism among them. The task will be accomplished by sharing four key avenues: a) common data format, b) clever use of repeating patterns, c) pattern prioritization based on design intent, and d) parallel processing. Under the concurrent optimization scheme, mask pattern priorities that we call as Mask Data Rank (MDR) are extracted from the design side, and repeating patterns are extracted from mask pattern data. These are fed-forward to mask writing and mask inspection sides. In mask writing, MDR is employed to optimize the writing conditions; and in Character Projection (CP) writing, repeating patterns are utilized for that purpose. In mask inspection, MDR is used to optimize defect judgment conditions, and repeating patterns are utilized for efficient review. For mask writing, we are developing a parallel e-beam writing system Multi Column Cell (MCC). Furthermore, we are developing an integrated diagnostic system for e-beam mask writer, and a technology for defect judgment technology based on defect printability in mask inspection. In this paper we describe details of our activity, its status, and some recent results.

It has been widely accepted that to ensure good yield in IC wafer manufacturing, early adaptation of DFM (Design for Manufacturability) guidelines in design phase is required and it is particularly true in Foundry business. Integrated foundry approaches for DFM guideline development were presented in this paper. With emphasis of process variations and process sensitivity impact on design patterns, we describe the procedure of the combination of rule-based and simulation-based lithographical hotspot pattern characterizations. An evaluation of process sensitivity metrics for analyzing potential pattern hotspots is then described. In addition, based on hotspot pattern severity, repeated patterns from different designs are saved into a pattern library as knowledge deposition tool and those patterns can be easily identified later in new designs through pattern search, which is much faster than simulation based hotspot detections. With this approach, a set of DFM compliance rules is derived to designs in the design implementation stage for both 110nm and 90nm technology nodes, striving to gain more yield, device performance, and improve time-to-volume production.

In this paper we present the method that NuFlare photomask inspection systems can use to strongly reduce pseudo detections by use of TK-CMI software. The NuFlare inspection system is capable to detect the smallest defects in the 45 and 32-nm nodes and has recently been introduced to production. It links up with a compute cluster with Takumi's Criticality-Marker Information software (TK-CMI). TK-CMI quickly analyzes the ~200GB post-OPC layout or multi-layer pre-OPC layout and assigns various types of criticality regions. The basic set of criticalities is made to address the challenges that typical maskmakers experience. The TKCMI system also supports design-intent-based criticalities. The NuFlare inspection system uses this full-mask criticality information and generates flexible inspection recipes that inspect low-criticality areas with relaxed sensitivity resulting in reduction of pseudo detections in such regions.

This paper describes a simple technique to improve the process latitude for contact and via printing. The technique applies a selective upsizing algorithm to the mask data during the mask preparation step. For each contact or via, the algorithm looks for available spaces by checking relevant layers near it. When spaces are available, selective edges of a contact or via will be sized to improve the process latitude. This paper describes algorithms used to implement this technique. Multiple designs of various design styles are used to demonstrate the effectiveness of the algorithms. The implications on mask preparation, mask making and wafer processing are also discussed.

Double patterning has gained prominence as the most likely lithographic methodology to help keep Moore's law going towards 32nm 1/2 pitch lithography. While solutions, to date, have focused mainly on gap splitting to avoid minimum spacing violations, the decomposition should, ideally, also attempt to optimize the process window of the decomposed masks. A major contributor to process window sensitivity is the correct placement of sub-resolvable assist features. These features are placed once the polygons of each mask are defined, i.e. post decomposition. If some awareness of this downstream process step is made available to the double patterning decomposition stage, then a more robust decomposition can be achieved.

Extreme ultraviolet lithography (EUVL) is the most promising lithographic technology to fabricate the next generation devices with a 20~30 nm feature size or smaller. The production of the EUVL mask blank is one of the critical issues to realize the EUVL because of various kinds of stringent requirements. For instance, a <+/-5 ppb/K thermal expansion coefficient (CTE) and a <30 nm surface flatness of the polished substrate, a high and uniform reflectivity at the 13~14 nm wavelength of the reflective multilayer film, and a low defect density as small as 30nm of the blank. Most of these requirements are different from the optical lithography mask blank and some are specific to the EUVL blank. We have continuously been developing all of key materials and processes essential to prepare the EUVL mask blank, and we showed a good progress in its performance improvement. Our low thermal expansion material (LTEM) showed the CTE properties requirements defined in SEMI P37, which were 0 +/- 5 ppb/K mean CTE at 22°C and < +/-3 ppb/K CTE spatial variation across 6 inch square substrate. ~30nm flatness was demonstrated on both front and back surfaces of the LTEM polished substrate, which was very close to the most stringent flatness requirement of SEMI P37. Ta-based absorber film and anti-reflective film were also developed. Their film properties almost met SEMI P38 class A, and the absorbers showed good etching and patterning performances with the inductively coupled plasma etching process. In addition, the thinner resist coating process was developed. As a consequence, Asahi Glass has a capability to deliver the ready-to-write EUVL blank which is the most suitable for the EUVL process developments by using the full field exposure tools.

Surface cleaning has become one of the most critical processes in photomask manufacturing in the last few years because of the demands for high cleaning efficiency with no film loss and no damage to fragile patterns. The requirement is getting tighter as the feature-size shrinks. In addition, EUV masks pose further unique challenges in the cleaning process, because of the reflective multilayer (ML) mask structure, which is sensitive to surface damage, and a more frequent cleaning requirement due to the lack of pellicle protection during handing and usage. To address the challenge of ML surface damage from EUV mask cleaning processes, this paper presents the chemical durability of Ru-capped ML blanks against two types of chemistries: a mixture of sulfuric acid and hydrogen peroxide (SPM) and ozonated water (DIO3). The authors found that SPM slightly oxidized the Ru capping layer, but with minimal effect to EUV reflectivity. It was observed that DIO3 damaged the Ru capping layer and resulted in a significant EUV reflectivity drop. An alloyed Ru-capping layer showed improved durability against DIO3 damage. The changes to the Ru-surface were characterized with atomic force microscopy (AFM) and X-ray photo electron spectroscopy (XPS).

The effect of mask structure with light shield area on the printability in EUV lithography was studied. When very thin absorber on EUVL mask is used for ULSI application, it then becomes necessary to create EUV light shield area on the mask in order to suppress possible leakage of EUV light from neighboring exposure shots. We proposed and fabricated two types of masks with very thin absorber and light shield area structure. For both types of masks we demonstrated high shield performances at light shield areas by employing a Small Field Exposure Tool (SFET).

A patterned TaN substrate, which is candidate for a mask absorber in extreme ultra-violet lithography (EUVL), was etched to have inclined sidewalls by using a Faraday cage system under the condition of a 2-step process that allowed the high etch selectivity of TaN over the resist. The sidewall angle (SWA) of the patterned substrate, which was in the shape of a parallelogram after etching, could be controlled by changing the slope of a substrate holder that was placed in the Faraday cage. The performance of an EUV mask, which contained the TaN absorber of an oblique pattern over the molybdenum/silicon multi-layer, was simulated for different cases of SWA. The results indicated that the optical properties, such as the critical dimension (CD), an offset in the CD bias between horizontal and vertical patterns (H-V bias), and a shift in the image position on the wafer, could be controlled by changing the SWA of the absorber stack. The simulation result showed that the effect of the SWA on the optical properties became more significant at larger thicknesses of the absorber and smaller sizes of the target CD. Nevertheless, the contrast of the aerial images was not significantly decreased because the shadow effect caused by either sidewall of the patterned substrate cancelled with each other.

Extreme Ultraviolet Lithography (EUVL) masks have residual stress induced by several thin films on low thermal expansion material (LTEM) substrates. The stressed thin films finally result in convex out-of-plane displacement (OPD) of several 100s of nm on the pattern side of the mask. Since EUVL masks are chucked on EUVL scanners differently from on e-beam writer, the mask pattern placement errors (PPE) are necessary to be corrected for to reduce overlay errors. In this paper, experimental results of pattern placement error correction using standard chrome on glass (COG) plate will be discussed together with simulations. Excellent agreement with simple bending theory is obtained. Suitability of the model to compensate for other EUVL-related PPEs due to mask non-flatness will be discussed.

We have developed an actinic full-field inspection system to detect multilayer phase defect with dark field imaging. With this system, programmed phase defects on a mask blank were observed. The system can detect phase defects caused by a 1.5 nm high and 60 nm wide protrusion on a multilayer surface. Background intensity and signal to background ratio (SBR) of the observed defect images are analyzed with simulation. The background intensities were calculated with the model that it is generated by light scattered from mask surface roughness. The result indicates that the larger outer NA (numerical aperture) leads to an increase in the background intensity. In this correlation of NA with the background intensity, the calculation and experimental results correspond well. The defect images were simulated using the point spread function (PSF) of flare generated by mirror surface roughness employing Fourier technique. The SBRs of simulated defect images corresponded well with the SBRs of the observed images. These results support the calculation and simulation models are proper.

The SEMATECH Berkeley Actinic Inspection Tool (AIT) is an EUV zoneplate microscope dedicated to photomask research. Recent upgrades have given the AIT imaging system selectable numerical aperture values of 0.25, 0.30, and 0.35 (4 equivalent). The highest of which provides resolution beyond the current generation of EUV lithography research tools, giving above 75% contrast for dense-line features with 100-nm half-pitch on the mask, and above 70% for 88-nm half-pitch. To improve the imaging system alignment, we used through-focus images of small contacts to extract aberration magnitudes and compare with modeling. The astigmatism magnitude reached a low value of 0.08 waves RMS. We present the results of performance benchmarking and repeatability tests including contrast, and line width measurements.

In this paper, we will report on our experimental and simulation results on the impact of EUVL mask absorber structure and of inspection system optics on mask defect detection sensitivity. We employed a commercial simulator EM-Suite (Panoramic Technology, Inc.) which calculated rigorously using FDTD (Finite-difference time-domain) method. By using various optical constants of absorber stacks, we calculated image contrasts and defect image signals as obtained from the mask defect inspection system. We evaluated the image contrast and the capability of detecting defects on the EUVL masks by using a new inspection tool made by NuFlare Technology, Inc. (NFT) and Advanced Mask Inspection Technology, Inc. (AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect inspection system using 199nm wavelength inspection optics. The programmed defect masks with LR-TaBN and LRTaSi absorbers were used which had various sized opaque and clear extension defects on hp-160nm, hp-225nm, and hp- 325nm line and space patterns. According to the analysis, reflectivity of EUVL mask absorber structures and the inspection optics have large influence on image contrast and defect sensitivity. It is very important to optimize absorber structure and inspection optics for the development of EUVL mask inspection technology, and for the improvement of performance of EUV lithographic systems.

We have used ASML's full field step-and-scan exposure tool for extreme ultraviolet lithography (EUVL), known as an Alpha Demo Tool, to investigate one of the critical issues identified for EUVL, defectivity associated with EUV masks. The main objective for this work was to investigate the infrastructure currently in place to examine defects on a EUV reticle and identify their consequence in exposed resist. Unlike many previous investigations this work looks at naturally occurring defects in a EUV exposed metal layer from a 45 nm node device. The EUV exposure was also integrated into a standard process flow where the other layers were patterned using more conventional 193-nm lithography techniques. This presentation correlates reticle level defectivity to resulting wafer exposures. Defect inspection data from both the 28xx family of KLA-Tencor wafer inspection tool and Terascan reticle inspection tools are presented. Defect populations were characterized with a KLA 5200 Review SEM. Observed defectivity modes were analyzed using both conventional defect inspection methodology as well as advanced techniques in order to gain further insight. We find good correlations between reticle level defects and the resulting wafer exposure defects.

We evaluated a new FIB-GAE (Focused Ion Beam-Gas Assisted Etching) repairing process for the absorber defects on EUVL mask. XeF₂ gas and H₂O gas were used as etching assist agent and etching stop agent respectively. The H₂O gas was used to oxidize Ta-nitride side-wall and to inactivate the remaining XeF₂ gas after the completion of defect repair. At the Photomask Japan 2008 we had reported that side-etching of Ta-nitride caused CD degradation in EUVL. In the present paper we report on the performance of defect repair by FIB, and of printability using SFET (Small Field Exposure Tool). The samples evaluated, were in form of bridge defects in hp225nm L/S pattern. The cross sectional SEM images certified that the newly developed H₂O gas process prevented side-etching damage to TaBN layer and made the side-wall close to vertical. The printability also showed excellent results. There were no significant CD changes in the defocus characterization of the defect repaired region. In its defect repair process, the FIB method showed no signs of scan damage on Cr buffered EUV mask. The repair accuracy and the application to narrow pitched pattern are also discussed.

Reduced design rules demand higher sensitivity of inspection, and thus small defects which did not affect printability before require repair now. The trend is expected to be similar in extreme ultraviolet lithography (EUVL) which is a promising candidate for sub 32 nm node devices due to high printing resolution. The appropriate repair tool for the small defects is a nanomachining system. An area which remains to be studied is the nano-machining system performance regarding repair of the defects without causing multilayer damage. Currently, nanomachining Z-depth controllability is 3 nm while the Ru-capping layer is 2.5 nm thick in a Buffer-less Ru-capped EUV mask. For this report, new repair processes are studied in conjunction with the machining behavior of the different EUVL mask layers. Repair applications to achieve the Edge Placement(EP) and Z-depth controllability for an optimal printability process window are discussed. Repair feasibility was determined using a EUV micro exposure tool (MET) and Actinic Imaging Tool (AIT) to evaluate repairs the 30 nm and 40 nm nodes. Finally, we will report the process margin of the repair through Slitho-EUVTM simulation by controlling side wall angle, Z-depth, and EP (Edge Placement) on the base of 3-dimensional experimental result.

EUV mask damage caused by Ga focused ion beam irradiation during the mask defect repair was studied. The concentration of Ga atom implanted in the multilayer through the buffer layer and distributions of recoil atoms were calculated by SRIM. The reflectivity of the multilayer was calculated from the Ga distribution below the capping layer surface. To validate the calculation, Ga focused ion beam was irradiated on the buffer layer. The EUV reflectivity was measured after the buffer layer etching process. The measured reflectivity change was considerably larger than the one predicted from the absorption of light by the implanted Ga. The large reflectivity loss was primarily due to the absorption of light by chromium silicide residue which was generated by the intermixing of the buffer and the capping layer. Both lowering of the acceleration voltage and using thicker buffer layer were found to be effective in reducing this intermixing. The reduction of the reflectivity loss by using thicker buffer layer was confirmed by our experiments. An aerial image of patterns with etching residue formed by the intermixing was simulated. When the thickness of the intermixed layer happened to be 8 nm and the size of the resulting residue was larger than 100 nm, then the impact of the estimated absorption by the residue on the linewidth of 32 nm hp line pattern became more than 5 %.

Step and Flash Imprint Lithography redefines nanoimprinting. This novel technique involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed leaving a patterned solid on the substrate. Compatibility with existing CMOS processes requires a mask infrastructure in which resolution, inspection and repair are all addressed. The purpose of this paper is to understand the limitations of inspection at half pitches of 32 nm and below. A 32 nm programmed defect mask was fabricated. Patterns included in the mask consisted of an SRAM Metal 1 cell, dense lines, and dense arrays of pillars. Programmed defect sizes started at 4 nm and increased to 48 nm in increments of 4 nm. Defects in both the mask and imprinted wafers were characterized scanning electron microscopy and the measured defect areas were calculated. These defects were then inspected using a KLA-T eS35 electron beam wafer inspection system. Defect sizes as small as 12 nm were detected, and detection limits were found to be a function of defect type.

Two essential process steps of the template fabrication chain are inspection and repair. The widely introduced gas assisted e-beam etching and deposition technique for mask repair offers crucial advantages, especially regarding the resolution capability. We started the evaluation of a new e-beam repair test stand based on the Zeiss MeRiT technology for UV-NIL template repair. For this purpose, templates with programmed defects of different shapes and sizes have been designed and fabricated. The repair experiments were focused on the development of recipes for quartz etching and deposition specifically tailored for NIL repair requirements Both, clear and opaque programmed defects have been repaired and the results have been analyzed. After recipe optimization, templates with repaired programmed defects have been imprinted on a Molecular Imprints Imprio 250 tool. By comparing template and imprint results we investigated the repair capability.

The discussion on reticle cost continues to raise questions by many in the semiconductor industry. The diamond industry developed a method to judge and grade diamonds. [1, 11] The diamond-marketing tool of "The 4Cs of Diamonds" and other slogans help explain the multiple, complex variables that determine the value of a particular stone. Understanding the critical factors of Carat, Clarity, Color, and Cut allows all customers to choose a gem that matches their unique desires. I apply the same principles of "The 4Cs of Diamonds" to develop an analogous method for rating and tracking reticle performance. I introduced the first 3Cs of reticle manufacturing during my BACUS presentation panel at SPIE in February 2008. [2] To these first 3Cs (Capital, Complexity, and Content), I now add a fourth, Cycle time. I will look at how our use of reticles changes by node and use "The 4Cs of Reticles" to develop the key performance indicators (KPI) that will help our industry set standards for evaluating reticle technology. Capital includes both cost and utilization. This includes tools, people, facilities, and support systems required for building the most critical reticles. Tools have highest value in the first two years of use, and each new technology node will likely increase the Capital cost of reticles. New technologies, specifications, and materials drive Complexity for reticles, including smaller feature size, increased optical proximity correction (OPC), and more levels at sub-wavelength. The large data files needed to create finer features require the use of the newest tools for writing, inspection, and repair. Content encompasses the customer's specifications and requirements, which the mask shop must meet. The specifications are critical because they drive wafer yield. A clear increase of the number of masking levels has occurred since the 90 nm node. Cycle time starts when the design is finished and lasts until the mask house ships the reticle to the fab. Depending on the level of Complexity, a reticle can take from as few as one, to more than forty, days to build. By using the 4Cs, I can show how the reticle build has changed from the 90 nm technology node. I will begin by delineating proposed KPIs for reticles.

The new Flume data communication protocol takes a unique approach to addressing the effects of latency in long-distance data transmission. In addition to managing the data itself through compression, delta processing and error correction, Flume eliminates the impact of latency by transmitting a continuous stream of data without ever pausing to wait for acknowledgements from the data receiver. Transmission times are accelerated by 5X - 100X and these speedups continue at least linearly with added bandwidth. A second, optional mode of operation, transmits separate pieces of the data to be transmitted to different locations which can then exchange data among themselves to recreate the complete data at all sites.

With each new process technology node chip designs increase in complexity and size, and mask data prep flows require more compute resources to maintain the desired turn around time (TAT) at a low cost. Securing highly scalable processing for each element of the flow - geometry processing, resolution enhancements and optical process correction, verification and fracture - has been the focal point so far. The utilization for different flow elements depends on the operation, the data hierarchy and the device type. This paper introduces a dynamic utilization driven compute resource control system applied to large scale parallel computation environment. The paper will analyze performance metrics TAT and throughput for a production system and discuss trade-offs of different parallelization approaches in data processing regarding interaction with dynamic resource control. The study focuses on 65nm and 45nm designs.

In preparation of the international Nano1 linewidth comparison on photomasks between 9 national metrology institutes, NIST and PTB have started a bilateral linewidth comparison in 2008, independent of and prior to the Nano1 comparison in order to test the suitability of the mask standards and the general approach to be used for the Nano1 comparison. This contribution describes the rationale of both comparisons, the design of the mask comparison standards to be used and the measurement methods applied for traceable photomask linewidth metrology at NIST and PTB.

The current photomask linewidth Standard Reference Material (SRM) supplied by the National Institute of Standards and Technology (NIST), SRM 2059, is the fifth generation of such standards for mask metrology. An in house optical microscope tool developed at NIST, called the NIST ultra-violet (UV) microscope, was used in transmission mode to calibrate the SRM 2059 photomasks. Due to the limitations of available optical models for determining the edge response in the UV microscope, the tool was used in a comparator mode. One of the masks was selected as a master standard - and the features on this mask were calibrated using traceable critical dimension atomic force microscope (CD-AFM) dimensional metrology. The optical measurements were then used to determine the relative offsets between the widths on the master standard and individual masks for sale to customers. At the time of these measurements, however, the uncertainties in the CD-AFM reference metrology on the master standard were larger than can now be achieved because the NIST single crystal critical dimension reference material (SCCDRM) project had not been completed. Using our CD-AFM at NIST, we have performed new measurements on the SRM 2059 master standard. The new AFM results are in agreement with the prior measurements and have expanded uncertainties approximately one fourth of those of the earlier results for sub-micrometer features. When the optical comparator data for customers masks are reanalyzed using these new AFM results, we expect to reduce the combined reported uncertainties for the linewidths on the actual SRMs by at least 40 % for the nominal 0.25 μm features.

Measurement of resist critical dimensions (CDs) utilizing a scanning electron microscope (SEM) based metrology system causes the resist to change due to irradiation effects of the electrons. A new and novel scanning approach has been developed in an effort to minimize the effects electron irradiation and exposure during the measurement process. This technique is especially pertinent in view of the tightening requirements for process control to achieve single digit CD uniformity on leading edge photo masks being produced today. The measurement of OPC features necessitates utilization of SEM based metrology due to resolution requirements, but the effects of high magnification imaging presents unique challenges. By controlling the scanned region of interest (ROI) it is possible to reduce exposure and irradiation effects. This paper will detail this new approach as it is utilized on the LWM9045 SEM Metrology system. The LWM9000SEM mask CD SEM was introduced earlier.

Photomask pattern sizes are usually defined by a one-dimensional Critical Dimension (CD). As mask pattern shapes become more complex, a single CD no longer provides sufficient information to characterize the mask feature. For simple square contacts, an area measurement is generally accepted as a better choice for determining contact uniformity. However, the area metric may not adequately characterize complex shapes; it does not lend itself to CD metrology and it ignores pattern placement. This paper investigates new ways of measuring complex mask shapes with aggressive Optical Proximity Correction (OPC). An example of more informative metric is center of gravity. This new metric will be compared to more traditional mask characterization variables like CD mean to target, CD uniformity, and Image Placement (IP). Wafer simulations of the mask shapes will be used to understand which mask pattern metrics are most representative of the image transferred to wafer images. The results will be discussed in terms of their potential to improve mask quality for 32nm technology and beyond.

We have developed a new method of accurately profiling and measuring of a mask shape by utilizing a Mask CD-SEM. The method is intended to realize high accuracy, stability and reproducibility of the Mask CD-SEM adopting an edge detection algorithm as the key technology used in CD-SEM for high accuracy CD measurement. In comparison with a conventional image processing method for contour profiling, this edge detection method is possible to create the profiles with much higher accuracy which is comparable with CD-SEM for semiconductor device CD measurement. This method realizes two-dimensional metrology for refined pattern that had been difficult to measure conventionally by utilizing high precision contour profile. In this report, we will introduce the algorithm in general, the experimental results and the application in practice. As shrinkage of design rule for semiconductor device has further advanced, an aggressive OPC (Optical Proximity Correction) is indispensable in RET (Resolution Enhancement Technology). From the view point of DFM (Design for Manufacturability), a dramatic increase of data processing cost for advanced MDP (Mask Data Preparation) for instance and surge of mask making cost have become a big concern to the device manufacturers. This is to say, demands for quality is becoming strenuous because of enormous quantity of data growth with increasing of refined pattern on photo mask manufacture. In the result, massive amount of simulated error occurs on mask inspection that causes lengthening of mask production and inspection period, cost increasing, and long delivery time. In a sense, it is a trade-off between the high accuracy RET and the mask production cost, while it gives a significant impact on the semiconductor market centered around the mask business. To cope with the problem, we propose the best method of a DFM solution using two-dimensional metrology for refined pattern.

The demands on CD metrology techniques in terms of both reproducibility and measurement uncertainty increase with decreasing critical dimensions (CD) on lithography masks. Additionally a full 3D characterization of the mask structures becomes more and more important to understand and control the printing behavior of state of the art photomasks. Furthermore, an extension of metrology characterization including material properties can provide the final puzzle pieces for a better correlation of mask metrology to wafer metrology. Here, optical metrology systems, especially at-wavelength systems, are very well suited to characterize structure features of a photomask regarding their printing behavior on a wafer. In particular scatterometry is able to provide a better understanding of the investigated structure and allows for modeling of secondary structure parameters as well as material composition. AMTC has a commercial scatterometer from n&k Technology (n&k 5700-CDRT) in use. This system measures the spectral transmission and reflection, the 0th diffraction order. Beside thin film characterization this system is used for CD and edge profile characterization, also. The analysis of the data uses a look-up table approach in combination with a database, which has been generated and can be expanded, respectively, using a RCWA based software. At PTB we have realized a new DUV hybrid scatterometer which combines essential elements of a radiometer, an ellipsometer, and a diffractometer. These two systems are different both in terms of the measurement modes, the data evaluation method and the Maxwell-solver used. Therefore we started to compare the performance of both systems to traditional metrology system for CD metrology and phase measurement. For this purpose we performed first comparative scatterometric measurements on a MoSi phase shifting mask.

Process control of line width and etch depth on the photomask production is more important as the industry moves toward 50nm node and beyond. In this paper, we report the ellipsometer-based scatterometry based metrology system that provides line width and resist thickness measurements on sub 50 nm node test masks for a mask process monitoring. Measurements were made with spectroscopic rotating compensator ellipsometer system. For analysis we made up modeling libraries with a 200 nm half pitch and checked and applied them to ADI and ACI measurements of binary and phase shift mask (PSM). We characterized the CD uniformity, linearity, thickness uniformity. Results show that linearity measured from fixed-pitch, varying line/space ratio targets show good correlation to top-down CD-SEM with R2 of more than 0.99. Resist thickness results show that depth bias is about 2nm between AFM and OCD in ADI step. The data show that optical CD measurements provide a nondestructive way to monitor mask processes with relatively little time loss from measurement step.

According to the 2007 edition of the ITRS roadmap, the requirement for CD uniformity of isolated lines on a binary or attenuated phase shift mask is 2.1nm (3σ) in 2008 and requires improvement to1.3 nm (3σ) in 2010. In order to meet the increasing demand for CD uniformity on photo masks, improved CD metrology is required. A next generation AFM, InSight^TM 3DAFM, has been developed to meet these increased requirements for advanced photo mask metrology. The new system achieves 2X improvement in CD and depth precision on advanced photo masks features over the previous generation 3D-AFM. This paper provides measurement data including depth, CD, and sidewall angle metrology. In addition the unique capabilities of damage-free defect inspection and Nanoimprint characterization by 3D AFM are presented.

The so-called Nanometer Comparator is the PTB vacuum length comparator which has been developed for high precision length metrology on measurement objects with micro- and nanostructured graduations, like e.g. line scales, incremental encoders or photomasks. The Nanometer Comparator allows to achieve smallest measurement uncertainties in the nm-range by use of vacuum laser interferometry for the displacement measurement. We will report on the achieved measurement performance of this high precision vacuum length comparator and the already started developments to substantially enhance its measurement capabilities by additional straightness measurement capabilities. The enhanced Nanometer Comparator will provide traceability for photomask pattern placement measurements in industry, also facing the challenges due to the increased requirements on registration metrology as set by the introduction of new lithography techniques like double patterning methods.

This paper reports on the current status of PROVE^TM - a new photomask registration and overlay metrology system currently under development at Carl Zeiss. The scope of the project is to design and build a photomask pattern placement metrology tool which is serving the 32 nm node. Performance specifications of the tool are actually driven by double exposure/ double patterning approaches which will help to extend the 193 nm lithography platforms, while keeping the semiconductor industry conform to ITRS roadmap requirements. A secondary requirement of pattern placement metrology tools is the CD measurement option for design features of interest. Combining both registration and CD measurement reduces the number of process operations a photomask has to encounter during manufacture. Optical design considerations are discussed, which led to the tool being designed for 193 nm illumination corresponding to at-wavelength metrology for most current and future photomask applications. The concept enables registration and CD metrology by transmitted or reflected light. The short wavelength together with a NA of 0.6 also provides sufficient resolution even at working distances compatible with the use of pellicles, hence enabling the tool for qualification of final, production ready masks. Imaging simulations with a rigorous Maxwell solver prove our chosen optical concept to be adequate for the various mask types (e.g. COG, MoSi, EUV) commonly used today and presumably in the future. The open concept does enable a higher NA for future, pellicle free applications.

Turn around time/cycle time is a key success criterion in the semiconductor photomask business. Therefore, global mask suppliers typically allocate work loads based on fab capability and utilization capacity. From a logistical point of view, the manufacturing location of a photomask should be transparent to the customer (mask user). Matching capability of production equipment and especially metrology tools is considered a key enabler to guarantee cross site manufacturing flexibility. Toppan, with manufacturing sites in eight countries worldwide, has an on-going program to match the registration metrology systems of all its production sites. This allows for manufacturing flexibility and risk mitigation.In cooperation with Vistec Semiconductor Systems, Toppan has recently completed a program to match the Vistec LMS IPRO systems at all production sites worldwide. Vistec has developed a new software feature which allows for significantly improved matching of LMS IPRO(x) registration metrology tools of various generations. We will report on the results of the global matching campaign of several of the leading Toppan sites.

Development and manufacture of advanced photomasks requires understanding the optical properties of mask materials and the ability to carefully monitor and control the film thickness, refractive index, and absorption of each film layer. Spectroscopic Ellipsometry (SE), a nondestructive optical analysis technique for determination of film thickness, refractive index, absorption, and film microstructure has been applied to many applications in current and emerging areas of photomask technology. This work surveys a variety of applications including analysis of fused silica mask blanks, imprint lithography templates, free-standing pellicles, deposited films of chromium, chromium oxide, MoSi, and multiple layers of these materials. For fused silica substrates we determine the optical properties (n & k) versus wavelength as well as the surface roughness. The near-surface index and surface roughness are used as indicators of surface polishing quality, which is an issue in the use of photomask substrates as template stamps in imprint lithography. Pellicles are free-standing films stretched over a metal frame. Because these thin pellicles are much thinner than the light coherence length, spectroscopic ellipsometry can determine the thickness, refractive index, and absorbance of the pellicle versus wavelength via interference between light reflecting from the upper and lower surfaces of the film. It is also possible to measure pellicles suspended over an underlying mask. The optical constants (n & k) of MoSi films vary widely with deposition conditions due to both composition and microstructure. Films optimized for 248 nm and 193 nm wavelengths have been analyzed. Spectroscopic ellipsometry shows good sensitivity to surface roughness and index gradients through the MoSi films. Multilayer masks such as NTAR have multiple absorbing layers such as chromium and chrome oxide. It is possible to simultaneously analyze multiple data sets acquired from the front side, from the back side through the substrate, and transmitted data through the stack. This increases the information content in the data, allowing more details from the multilayer to be determined. It is also possible to measure the birefringence in mask substrates and coated masks by using ellipsometry in transmission mode. By establishing a known polarization state incident on the mask it is possible to analyze the polarization after transmission to determine the phase difference, which is used to measure the birefringence of the sample. For patterned structures such as gratings it is possible to measure polarization-dependent diffraction effects versus angle. Measurement can be made in either reflection or transmission mode. It is possible to independently measure both s- and p-polarization components and compare to theory. As photomasks become more complex, with increasing numbers of layers (such as multilayer mirrors for EUV masks) in-situ ellipsometry shows great promise, providing the ultimate characterization of each film by allowing measurement in real-time as each layer is added to the mask structure.

Today reticle costs become one of the main contributors in the cost of manufacturing of advanced logic products. Especially for low volume projects as of product sampling as well as design and product verifications the saving of reticle costs becomes worthwhile. Multi level reticles are the combination of more then one lithographical layer on one physical reticle. Due to this approach the physical amount of reticles per tape out will be reduced and thereby also the costs for reticles will be significantly decreased. The multi level reticle approach is implemented as standard option in the INFINEON Technologies tape out flow for advanced logic products. This means dependent on forecasted volume and chip size it could be decided to tape out a project on multi level- or single level reticle. Technical setup, reticle layout, specification, CAD flow and experience in daily work using multi level reticles in different design nodes will be shown. Reticle cost advantage versus reduced throughput will be discussed.

Reticle cost and cycle time to deliver new circuit designs to a wafer fab remain key focus areas for advanced semiconductor manufacturing and new product development. Resolution enhancement techniques like optical proximity correction as applied to critical layers have increased the burden on mask data preparation and reticle writing steps of the mask making flow. The growing data volume and complexity of designs must be reduced to a perfect image on a reticle in the shortest time possible against computer and machine constraints. Continued dependence on 193 nm wavelength exposure in extremely low k₁ lithography exacerbates the underlying trends. Two important factors come together to drive the economics and performance of the reticle line: the complexity of the designs and the productivity of e-beam writing tools. The designs, OPC methods, and writing tool capabilities continue to evolve with each node of technology. The study builds on prior evaluations to look at fundamental pattern complexity across 90nm, 65nm, and 45nm logic designs using the gate and metal-1 critical layers. The writing tool throughput testing uses a range of standard patterns to establish shot limited performance as a calibration method for arbitrary designs. Node to node design and tool to tool generation comparisons highlight actual step changes in complexity and capability by introducing new quantitative methods, benchmarking metrics, and testing strategies. The findings are projected into the future using design complexity and writing tool trends to suggest implications about reticle cost, cycle time, or possible gaps in technology development.

Two main challenges of future mask making are the decreasing throughput of the pattern generators and the insufficient line edge roughness of the resist structures. The increasing design complexity with smaller feature sizes combined with additional pattern elements of the Optical Proximity Correction generates huge data volumes which reduce correspondingly the throughput of conventional single e-beam pattern generators. On the other hand the achievable line edge roughness when using sensitive chemically amplified resists does not fulfill the future requirements. The application of less sensitive resists may provide an improved roughness, however on account of throughput, as well. To overcome this challenge a proton multi-beam pattern generator is developed [1]. Starting with a highly parallel broad beam, an aperture-plate is used to generate thousands of separate spot beams. These beams pass through a blanking-plate unit, based on a CMOS device for de-multiplexing the writing data and equipped with electrodes placed around the apertures switching the beams "on" or "off", dependent on the desired pattern. The beam array is demagnified by a 200x reduction optics and the exposure of the entire substrate is done by a continuous moving stage. One major challenge is the fabrication of the required high aspect deflection electrodes and their connection to the CMOS device. One approach is to combine a post-processed CMOS chip with a MEMS component containing the deflection electrodes and to realize the electrical connection of both by vertical integration techniques. For the evaluation and assessment of this considered scheme and fabrication technique, a proof-of-concept deflection unit has been realized and tested. Our design is based on the generation of the deflection electrodes in a silicon membrane by etching trenches and oxide filling afterwards. In a 5mm x 5mm area 43,000 apertures with the corresponding electrodes have been structured and wired individually or in groups with aluminum lines. The aperture-plate for shaping the beams has been aligned and mounted on top of the blanking-plate. Afterwards this sandwich has been fixed on a base-plate with a pin plug as interface. The electrical connection has been performed with a standard chip bonding process to the aluminum pads on the blanking-plate. Finally, the proof-of-concept deflection unit was evaluated in a test bench. The results of electrical- and exposure tests are presented and discussed in detail.