EUV lithography has been delayed due to well-known issues such as source power, debris, pellicle, etc. for high volume
manufacturing. For this reason, conventional optical lithography has been developed to cover more generations with
various kinds of Resolution Enhancement Techniques (RETs) and new process technology like Multiple Patterning
Technology (MPT). Presently, industry lithographers have been adopting two similar techniques of the computational
OPC scheme such as Inverse Lithography Technology (ILT) and Source Mask Optimization (SMO) . Sub-20 nm node
masks including these technologies are very difficult to fabricate due to many small features which are near the limits of
mask patterning process. Therefore, these masks require the unseen level of difficulty for inspection. In other words,
from the viewpoint of mask inspection, it is very challenging to maintain maximum sensitivities on main features and
minimum detection rates on the Sub-Resolution Assist Features (SRAFs). This paper describes the proper technique as
the alternative solution to overcome these critical issues with Aerial Imaging (AI) inspection and High Resolution (HR)
With the advent of system-on-chip (SOC) devices, resolving typical problems of composite designs is getting more urgent. The continuous effort for achieving tighter critical dimension (CD) tolerances together with the known phenomena of pattern density loading makes the mask fidelity issue for SOC technology a unique and prominent issue. The typical characteristic of an SOC with respect to CD control is the diversity of linewidths and pattern density over the chip. This paper presents the metrology software called Linewidth Bias Monitor (LBM) as a method to characterize pattern-loading effects on an SOC.
The reduction of wavelength in optical lithography and the use of enhancement techniques like phase shift technology, optical proximity correction (OPC), or off-axis illumination, lead to new specifications for advanced photomasks: a challenge for cost effective mask qualification. `Q-CAP', the Qualification Cluster for Advanced Photomasks, comprising different inspection tools (a photomask defect inspection station, a CD metrology system, a photomask review station and a stepper simulation software tool) was developed to face these new requirements. This paper will show the performance and reliability of quality assessment using the Q-CAP cluster tool for inspection and qualification of photomasks. Special attention is paid to a key issue of mask qualification: the impact of CD deviations, loss of pattern fidelity-- especially for OPC pattern and mask defects on wafer level.
This paper examines the effects of mask printability of various OPC defect types on a MoSi APSM mask using an MSM-100 AIMS tool operating at 248nm as a printability prediction tool. Printability analysis will be used to address differences in intensity, image capture wavelength, defocus, defect size, type, and placement on two substrate materials. Defect correlation to photomask CD error, aerial image intensity error, and MEEF on high-end KrF photomasks will also be studied.
CD uniformity is one of the key discussion topics in the ramp-up process of new technologies. The impact of mask quality is getting more and more attention in this process. The paper presents improving wafer CD uniformity control by application of new reticle CD qualification procedure. The new procedure is based on combining conventional CD metrology and Linewidth Bias Monitor (LBM) as a standard part of mask inspection.
The process of manufacturing and inspecting 150nm generation reticles, incorporating RETs - Resolution Enhancement Technologies - is discussed. Some of the RETs applied at the lithography stage while exposing the wafer, such as OAI - Off Axis Illumination, others RET are being incorporated into the reticle, such as OPC - Optical Proximity Correction - and PSM - Phase Shift is discussed. Many relevant aspects are discussed in this paper such as the ability to produce those critical layers while keeping good CD linearity, and the ability to detect OPC related defects with current reticle inspection technology.
Detection of reticle CD errors appears to be one of the most critical challenges for low-k1 lithography, where CD accuracy, as mean-to-normal and mask error factor determine most of wafer CD budget. Measurements of reticle CDs are always a difficult process, as the mask manufacturer need to know the critical areas on the masks where he has to execute the measurements. This information is not generally available and if it is available, the number of measurements can be extremely large, in particular for system-on-a-chip devices with multiple critical number of measurements can be extremely large, in particular for system-on-a-chip devices with multiple critical areas resulting from the multiple electrical functions located on a chip. For these reasons, it becomes extremely interesting to execute the reticle CD metrology in a 'two-step' approach: first, detection of 'global' CD errors during the reticle inspection, followed by the second step, where the CD measurements will be executed only in those areas where the global CD error algorithm has detected errors large enough to affect wafer CD control. In this way, the among of CD measurements will be reduced to a manageable number and more important, measurements will be executed only in those area that have large errors. However, there is one critical concern in this approach, that is the capability of the 'global CD error' algorithm to accurately detect CD errors in areas with various chrome density as well as to detect CD errors of minimum 20 to 30nm which represent the specification of a good reticle for low-k1 lithography. In this paper, we report on a layout design with programmed CD errors and on the first result of applying the global CD error algorithm to detect these errors. The layout with programmed CD errors, is a multi-die per reticle case with several levels of CD errors, from global shifts in mean CD, to errors programed in a regular or in a random array inside the reticle active area. This design stresses the measurement algorithm as the programmed CD errors are combined with chrome density varying across the die, by a factor of 1 to 2.5X. One of the useful features of the proposed algorithm, detection of large CD fingerprint errors on the reticle, has been demonstrated in this work.
Using a failure analysis-driven yield enhancements concept, based on an optimization of the mask manufacturing process and UV reticle inspection is studied and shown to improve the contact layer quality. This is achieved by relating various manufacturing processes to very fine tuned contact defect detection. In this way, selecting an optimized manufacturing process with fine-tuned inspection setup is achieved in a controlled manner. This paper presents a study, performed on a specially designed test reticle, which simulates production contact layers of design rule 250nm, 180nm and 150nm. This paper focuses on the use of advanced UV reticle inspection techniques as part of the process optimization cycle. Current inspection equipment uses traditional and insufficient methods of small contact-hole inspection and review.
While the semiconductor industry is following a very aggressive roadmap without a corresponding reduction in exposure wavelength, the role of resolution enhancement techniques like PSM and OPC is becoming more and more important. Mask making for these advanced techniques is one of the most crucial parts in making these techniques work. Mask inspection is one of the major challenges in the mask making process, as it is one of the most performance critical steps in the entire mask making process. Especially contact or OPC patterns show difficulties in die-to-database inspection as the CAD data asks for square corners. LPC is a mask enhancement technique improving image quality and CD linearity for laser pattern generators. The paper present the impact of Laser Proximity Correction on contact and line patterns of 0.18 micrometers generation. The LBM is used to characterize Cd uniformity improvement of the entire plate.
The reduction of wavelength in optical lithography, phase shift technology and optical proximity correction (OPC), requires a rapid increase in cost effective qualification of photomasks. The knowledge about CD variation, loss of pattern fidelity especially for OPC pattern and mask defects concerning the impact on wafer level is becoming a key issue for mask quality assessment. As part of the European Community supported ESPRIT projection 'Q-CAP', a new cluster concept has been developed, which allows the combination of hardware tools as well as software tools via network communication. It is designed to be open for any tool manufacturer and mask hose. The bi-directional network access allows the exchange of all relevant mask data including grayscale images, measurement results, lithography parameters, defect coordinates, layout data, process data etc. and its storage to a SQL database. The system uses SEMI format descriptions as well as standard network hardware and software components for the client server communication. Each tool is used mainly to perform its specific application without using expensive time to perform optional analysis, but the availability of the database allows each component to share the full data ste gathered by all components. Therefore, the cluster can be considered as one single virtual tool. The paper shows the advantage of the cluster approach, the benefits of the tools linked together already, and a vision of a mask house in the near future.
In this paper a new approach of concurrent CD-uniformity monitoring is presented. This is achieved by using the Linewidth Bias Monitoring (LBM) tool, which utilizes data collected during the reticle inspection to concurrently generate real-time line width monitoring with superb precision without affecting inspection time or results. The capabilities of the LBM are presented by a specially designed test-plate, establishing the tool precision and repeatability. Analysis of case studies based on various production plates demonstrates the contribution to process control and mask fidelity.
Inspection is one of the major challenges in mask making, as it is one of its most performance crucial steps in the entire mask making process. Especially contact patterns show difficulties in die-to-database inspection as the CAD data asks for square corners. The paper presents the impact of Laser Proximity Correction (LPC) on the inspectability of contact and line patterns. LPC is a mask enhancement technique improving image quality and CD linearity for laser pattern generators. The use of the linewidth bias monitor tool in order to characterize CD uniformity over the entire plate is demonstrated.
Low-k1 lithography requires enhancement techniques like phase shift and OPC. These techniques impose new and challenging specifications on photomasks. A development to establish means and methods to verify corner rounding, line end shortening, defect printability and the size of jogs, serifs and assist lines in a production worthy manner is based on the assessment of mask production data through a new cluster software tool which combines the output data of a mask defect inspection system, a CD metrology system, an AIMS based mask review station and printing simulation results. Possible definitions of new type photomask quality criteria are discussed and measurement procedures are proposed. As a key application the review of critical features on reticles (OPC, classical defects, contact printability, etc.) at changing stepper conditions ((lambda) , N.A., (sigma) ) is discussed. The concept and the development status of a Photomask Qualification Cluster is presented and early performance results are examined against the target values which are a defect detection sensitivity of 125 nm, optical resolution of 200 nm lines for assist line assessment, CD measurement on lines, contacts and OPC structures with 5 nm repeatability and mask pattern fidelity assessment at printing conditions down to 500 nm lines at reticle level.
Sub-wavelength or Super-resolution lithography requires us to review defects after reticle inspection, be it at the mask house or at incoming inspection, with a completely new approach. With the advent of UV reticle inspection for the 0.25 micrometer and below regime, the lithography engineer in a wafer fab will ask for much more detailed classification and characterization of a reticle. While reticles are supposedly 100% defect free when they arrive at the customer, a detailed analysis of any potential printable defect is done by fab engineers as well as many mask engineers. A time consuming and QUALITATIVE analysis is often performed by AIMS metrology, however, no real QUANTITATIVE estimate of the 'printability' can be given. This paper discusses the solution of using fast aerial image analysis of defect information gathered by an advanced UV inspection system, with accurate printability prediction. The described methodology is on-line, real-time, and can be performed in an automatic mode with any inspection.
Latest trends in optical lithography will dramatically change the way we need to look at defect printability and the impact that defects have on the performance of our devices. The prediction is, that linewidth variations will have the most severe impact, causing devices to perform under specification, or at least costing the manufacturers substantial photo limited yield by having to bin die in lower speed performance bins. A mask error enhancement factor may actually make defect print more severe in certain pattern, context, and linewidth variations across the pate will cause severe problems in the device manufacturing process to maintain ACLV at an acceptable level. Having to use RET technologies, such as OPC and PSM, may actually aggravate the printability problems. In this study, a special reticle design was used to investigate defect sizes, location and permutation, to evaluate: (i) defect sensitivity and capture in an advanced reticle inspection system, (ii) printability prediction using a sophisticated wafer image simulation software package, (iii) printability of 'traditional' vs. hidden linewidth error defects, (iv) the true CD impact of a given defect on LW performance using an advanced CD-SEM.
With the advance of photolithography technology into the super-resolution regime, reticle features are becoming denser and their dimensions are shrinking. This leads to much stricter design rules, which include a decrease in the dimensions of the critical defects needed to be detected. Orbot-Applied's new Improved Image Acquisition module has been developed as a means of meeting the rising demand in defect detection capability and integrated into RT-8000ES Die-to-Database reticle inspection system. The main purpose of this evaluation was to test the system's performance under difficult production conditions in its highest defect detection sensitivities.
As design rules in high-end photo-lithographic reticles become tighter, the monitoring of line-width variations becomes more vital in the quality control of advance reticle manufacturing processes. In this paper a new concept of operation is presented, for using an inspection tool in the monitoring of line-width variants for the purpose improving such quality control. The inspection tool use in this paper, is Orbot-Applied's RT8000ES Reticle Inspection tool, in which the newly developed Line Width Error Detector is embedded.
The significance of line width control in mask production has become greater with the lessening of defect size. There are two conventional methods used for controlling line widths dimensions which employed in the manufacturing of masks for sub micron devices. These two methods are the critical dimensions (CD) measurement and the detection of edge defects. Achieving reliable and accurate control of line width errors is one of the most challenging tasks in mask production. Neither of the two methods cited above (namely CD measurement and the detection of edge defects) guarantees the detection of line width errors with good sensitivity over the whole mask area. This stems from the fact that CD measurement provides only statistical data on the mask features whereas applying edge defect detection method checks defects on each edge by itself, and does not supply information on the combined result of error detection on two adjacent edges. For example, a combination of a small edge defect together with a CD non- uniformity which are both within the allowed tolerance, may yield a significant line width error, which will not be detected using the conventional methods (see figure 1). A new approach for the detection of line width errors which overcomes this difficulty is presented. Based on this approach, a new sensitive line width error detector was developed and added to Orbot's RT-8000 die-to-database reticle inspection system. This innovative detector operates continuously during the mask inspection process and scans (inspects) the entire area of the reticle for line width errors. The detection is based on a comparison of measured line width that are taken on both the design database and the scanned image of the reticle. In section 2, the motivation for developing this new detector is presented. The section covers an analysis of various defect types, which are difficult to detect using conventional edge detection methods or, alternatively, CD measurements. In section 3, the basic concept of the new approach is introduced together with a description of the new detector and its characteristics. In section 4, the calibration process that took place in order to achieve reliable and repeatable line width measurements is presented. The description of an experiments conducted in order to evaluate the sensitivity of the new detector is given in section 5, followed by a report of the results of this evaluation. The conclusions are presented in section 6.
The ability to inspect sub-micron features is an essential need for the manufacturing of advanced reticles. The shrinking of the minimal line width and the need for detecting smaller defects present a challenge for die-to-database reticle inspection. To meet this challenge, Orbot-Applied has developed an improved image acquisition (IIA) method and integrated it into its new RT-8000ES Die-to-Database reticle inspection system. The introduction of the IIA module made possible the detection of smaller defects and the ability to inspect smaller features, while maintaining all the other advantages of the field proven RT-8000 system. The evaluation of the RT-8000ES performance included scanning special test reticles with sub-micron features, containing different types of programmed defects of varying sizes. The evaluations's results show the RT-8000ES has the ability to inspect advanced reticles with lines down to 0.6 micron in width, while detecting defects as small as 0.15 microns, with no false defects. With this new improved image acquisition capability, the RT-8000ES has the ability to inspect current and future advanced reticles with high defect detection sensitivity and high reliability.
Controlling line width error is one of the most challenging tasks in mask production. Current methods for monitoring line width are based on either CD measurements or edge defect detection. Neither method guarantees the detection of line width errors with good sensitivity over the whole mask area. For example, a combination of small edge defect together with CD non-uniformity within the allowed tolerance, can yield a significant line width error, which will not be detected using conventional methods. In this paper we are presenting a new approach for line width error detection. The method, a new feature of Orbot's RT-8000 die-to-database Reticle Inspection System, is a sensitive detector that operates during the inspection of all the reticle's area. The detection is based on a comparison of measured line widths on both the database and the scanned image ofthe reticle. In section 2, the motivation for this new detector is driven. An analysis of various defect types, which are difficult to detected using edge detection approach or CD measurements, is presented. In section 3, the basic concept of the new approach is introduced together with a description of the new detector and it's characteristics. In section 4, the calibration process that took place in order to evaluate the sensitivity of the detector is described. The experimental results of this evaluation are reported in section 5.
256 Mbit DRAM devices pose a great challenge to the mask manufacturers. Shrinking kne widths,
tighter CD requirements, new lithography enhancement techniques, dense data bases, and higher
sensitMty to half-tone defects require advanced process and inspection systems. The improvements
and changes in mask manufacturing are translated into three main characteristics of a dietodatabase
inspection system: Image quality, reference data injection and defect detection. In order to meet the
challenge of inspecting 256 Mbit DRAM masks various enhancements need to be implemented in die..
to-database inspection systems which bring the above characteristics to the required level and supply
the mask maker with a highly reliable and sensitive tool.
With optical lithography prevailing into the year 2000, super-resolution processes pose a multitude of new challenges to the lithographer. Isolated to nested feature bias calls for 'pre- distorting' the photomask to compensate for proximity effects and print and etch biases in the mask and wafer manufacturing process. OPC (optical proximity correction) techniques have become a reality for sub-halfmicron lithography, and have initiated many discussions looking at the manufacturability of OPC masks. Regaining the lost DOF (depth of focus) due to ever shorter printing wavelength, and increasing yields by expanding process latitude have many IC manufacturers looking into PSMs (phase shift masks) as a viable but expensive enhancement technique for several [2-6] layers of the total [18-26] device mask set. This paper addresses manufacturability issues of various combinations of 'enhancement' masks.
The development and production of 64 and 256 Mbit DRAMs presents new challenges to mask defect detection. As happened during the development of previous generations of DRAMs, the decrease in line/space design rule dictates a similar decrease in the specification of mask defect size. This trend introduces new technologies and new requirements. This paper is concerned with two evolving technologies: layout modification for optical proximity correction (OPC) and phase-shift masks (PSM). The new technologies pose many issues for the mask maker. In this paper the defect detection is addressed. In section 2 few cases of OPC reticle inspection are presented while in section 3 the defect detection of PSM is discussed.
This report describes the RT-8000 product line of advanced reticle inspection systems for 64 and 256 Mbit DRAMs. The description is given from the system designer point of view. The main issues that are discussed are the methodologies used in the early phase of design and the design guidelines that help to meet the marketing goals. The central subject is the system architecture and its relation to the marketing needs.
Mask defect specification is derived from the needs of IC makers. It is primarily based on the wafer design rule. The specification relates to many issues that are usually defined and tested separately. In this paper we are concerned with the relation between edge defect specification and CD tolerance. The main problem with a combination of errors is how to handle the case of two errors of different kinds that are both below the specification, when considered separately, but their total change in edge position is larger than the edge defect specification. By convention, CD errors are automatically eliminated during automatic defect inspection by bias correction. Therefore, the inspection machine actually processes a database representation that matches the scanned image of the inspected die as best as possible. Thus the detection of combinations of global CD errors and edge extensions is prevented. An analysis of the problem is presented. A novel approach is suggested by which the user may optionally take into account CD errors together with edge defects during inspection. The experimental results are reported and initial conclusions are drawn.
The relation between the accuracy of the database representation and the inspection quality is discussed. In order to visualize the problems, a simplified model of an inspection machine is described. Using this model various aspects of database accuracy are presented. It is shown that some of the conventional methods for digitization of trapezoids, e.g. Brezenham method, may cause pixel-positioning errors and dropouts between figures. A better approach that is based on high precision subpixel addressing is proposed and its implication on reducing the database inaccuracy is proved.
A new scheme for automatic defect classification and sizing is presented. The new scheme is developed for improving the overall production of automatic die-to-database reticle inspection equipment for defect detection. The new scheme replaces the time-consuming, inaccurate and non-repeatable traditional methods that are based on human reviewing and verification of defects with the aid of relatively crude image processing electronics. In order to overcome these limitations, a double-tier scheme has been developed for automatic defect classification and sizing (ADCS). The fundamentals of this scheme are presented. The image processing algorithms are described and their overall performance is evaluated using various test and production masks. The reported scheme represents a practical precise and accurate method for automatic classification and sizing.