Sub-resolution assist feature (SRAF) insertion techniques have been effectively used for a long time now to increase process latitude in the lithography patterning process. Rule-based SRAF and model-based SRAF are complementary solutions, and each has its own benefits, depending on the objectives of applications and the criticality of the impact on manufacturing yield, efficiency, and productivity. Rule-based SRAF provides superior geometric output consistency and faster runtime performance, but the associated recipe development time can be of concern. Model-based SRAF provides better coverage for more complicated pattern structures in terms of shapes and sizes, with considerably less time required for recipe development, although consistency and performance may be impacted. In this paper, we introduce a new model-assisted template extraction (MATE) SRAF solution, which employs decision tree learning in a model-based solution to provide the benefits of both rule-based and model-based SRAF insertion approaches. The MATE solution is designed to automate the creation of rules/templates for SRAF insertion, and is based on the SRAF placement predicted by model-based solutions. The MATE SRAF recipe provides optimum lithographic quality in relation to various manufacturing aspects in a very short time, compared to traditional methods of rule optimization. Experiments were done using memory device pattern layouts to compare the MATE solution to existing model-based SRAF and pixelated SRAF approaches, based on lithographic process window quality, runtime performance, and geometric output consistency.
As technology node has been shrinking for bit growth, various technologies have been developed for high productivity. Nevertheless, lithography technology is close to its limit. In order to overcome these limits, EUV(Extreme Ultraviolet Lithography) and DSA(Directed Self-Assembly) are being developed, but there still exists problems for mass production. Currently, all lithography technology developments focus on solving the problems related to fine patterning and widening process window.
One of the technologies is NTD(Negative Tone Development) which uses inverse development compared to PTD(Positive Tone Development). The exposed area is eliminated by positive developer in PTD, whereas the exposed area is remained in NTD. It is well known that NTD has better characteristics compared to PTD in terms of DOF(Depth of Focus) margin, MEEF(Mask Error Enhancement Factor), and LER(Line End Roughness) for both small contact holes and isolated spaces [1]. Contact hole patterning is especially more difficult than space patterning because of the lower image contrast and smaller process window [2]. Thus, we have focused on the trend of both NTD and PTD contact hole patterns in various environments. We have analyzed optical performance of both NTD and PTD according to size and pitch by SMO(Source Mask Optimization) software. Moreover, the simulation result of NTD process was compared with the NTD wafer level performance and the process window variation of NTD was characterized through both results. This result will be a good guideline to avoid DoF loss when using NTD process for contact layers with various contact types.
In this paper, we studied the impact of different sources on various combinations of pattern sizes and pitches while estimating DOF trends aside from source and pattern types.
It is a distinctive feature of the metal contact layout in NAND flash memory devices that there are small-pitch contact patterns and random-pitch contact patterns in one layout. This kind of pitch difference between cell array patterns and isolated single patterns hadn’t had a decisive effect on wafers when the illumination condition is not aggressive. However, the pattern pitch difference has caused various problems including the best focus shift due to extreme illuminations. The common DOF margin of a contact layout is degraded when the best focus depth for each pattern is variable. Mask topography effect is well known for the major cause of best focus shift between contact patterns which have different pitches. The demand for device technology node shrink for production cost reduction has required adoption of hyper NA illumination conditions, and this aggressive illumination made it hard to secure an enough common DOF margin due to the best focus shift. In this work, the best focus shift phenomenon among different-pitch patterns caused by mask 3D effects is studied according to the various illumination conditions. It is found that the more aggressive illumination condition is and the bigger the pitch difference among patterns in one layout is, the bigger the best focus shift become. Also, we suggest the solution for avoiding this DOF margin degradation, which is SRAF optimization.
In this paper, we will evaluate model assisted rule base SRAF. Model assisted rule base SRAF
combines the advantage of both model based SRAF and rule base SRAF to ensure high process margin
without the mask making difficulty with stable wafer output. Model will assist in generating a common rule
for rule based SRAF. Method to extract the rule from the models will first be discussed. Model assisted rule
based SRAF will be applied to 3Xnm DRAM contact. Evaluation and analysis of the simulated and actual
wafer result will be discussed. Our wafer result showed that by applying Model assisted rule based SRAF
showed nearly equal performance to models based SRAF with clearly better stability and mask fabrication
feasibility.
As the DRAM node shrinks down to its natural limit, photo lithography is encountering many difficulties.
3Xnm DRAM node seems to be the limit for ArF Immersion. Until the arrival of EUV, double patterning (DPT) or
spacer double patterning (SPT) seems like the next solution. But the problem with DPT or SPT is that both increases
process step their by increasing the final costs of the device. So limiting the use of DPT or SPT is very important for
device fabrication. For 3Xnm DRAM, storage node is one of the candidates to eliminate DPT or SPT process. But this
method may cost lower process margin and degradation of pattern image. So, solution to these problems is very crucial.
In this study, we will realize storage node (SN) pattern for 3Xnm DRAM node with improved process margin. First we
will discuss selection of illumination for optimal condition second, correction of the mask will be introduced. We will
also talk about the usage of various RET such as model based assist feature. Value such as DOF, EL and CDU (critical
dimension uniformity) will be evaluated and analyzed.
Generally, rule based optical proximity correction (OPC) together with conventional illumination is used for contact layers, because it is simple to handle and processing times are short. As the design rule is getting smaller, it becomes more difficult to accurately control critical dimension (CD) variation because of influence by nearby contact holes pattern. Especially, random contact hole shows greater amount of CD difference between X and Y direction compared to array contact holes. Several resolution enhancement techniques (RET) were used to resolve this kind of problem, but didn't meet the overall expectations.
In this paper, we will present the results for novel contact hole model-based OPC for sub 60nm memory device. First, model calibration method will be proposed for contact holes pattern, which utilizes two thousands of real contact holes pattern to improve model accuracy in full chip. Second, verification method will be proposed to check weak points on full chip using model based verification. Finally, method for further enhancing CD variation within 5nm for model based OPC will be discussed using Die-to-Database Verification.
Recently, the dramatic acceleration in dimensional shrink of DRAM memory devices has been observed. For sub 60 nm memory device, we suggest the following method of optical proximity correction (OPC) to enhance the critical dimension uniformity (CDU). In order to enhance CD variation of each transistor, hundreds of thousand transistor CD data were used through design based metrology (DBM) system. In a traditional OPC modeling method, it is difficult to realize enhancement of CD variation on chip because of the limitation of OPC feedback data.
Even though optical properties are surely understood from recent computational lithography models, there are so many abnormalities like mask effect, thermal effect from the wafer process, and etch bias variation of the etching process. Especially, etch bias is too complicate to predict since it is related to variations such as space among adjacent patterns, the density of neighboring patterns and so on.
In this paper, process proximity correction (PPC) adopting the pattern to pattern matching method is used with huge amount of CD data from real wafer. This is the method which corrects CD bias with respect to each pattern by matching the same coordinates. New PPC method for enhancement of full chip CD variation is proposed which automatically corrects off-targeted feature by using full chip CD measurement data of DBM system. Thus, gate CDU of sub 60 nm node is reduced by using new PPC method. Analysis showed that our novel PPC method enhanced CD variation of full chip up to 20 percent.
As the design rule shrinks to its natural limit, reduction in lithography process margin and high Critical
Dimension (CD) error gives rise to use of many Resolution Enhancement Techniques (RET). Recently, one the popular
RET method to solve the above problem is polarized illumination. It is used to enhance the reduced lithography process
margin and enhance CD uniformity. Polarization lithography basically uses one sided polarized light source. Therefore
process margin increases for smaller design rule patterns. In this paper, we will present the results for polarized
illumination based Optical proximity Correction (OPC) for sub-60nm memory device. First, models for polarization
based and un-polarization based method will be compared for its model accuracy. Second, the process margin
improvement for polarized and un-polarized illumination will be compared and analyzed for poly layer of sub-60nm
memory device. Finally, method for further enhancing CD error within 5% for polarized OPC model will be discussed.
Recently, as the design rule shrinks so does the CD tolerance. Therefore, the importance of simulation and OPC accuracy is increasing. In the past, when pattern size was large, rule-based OPC was acceptable but as the design rule shrinks accuracy of OPC turned to model-based OPC and almost all device uses this method. Model-based OPC is based on parameter fitting it has Model-Residual-Error (MRE). Due to this error the accuracy of the model has limitations. Usually variable-threshold or vector model is applied to the model in order to cut down the MRE. But still, size of the MRE is too large compared to CD tolerance. Currently, further development of model-based OPC resulted in creation of both model and rule-based OPC. This is called Hybrid OPC method. Hybrid-OPC method is based on model OPC but MRE can be lowered using rule bias to retarget the design data. But this method makes it difficult to retarget the design data in that rule biasing result is hard to predict after the model-based OPC operation.
In this paper, we propose New Hybrid OPC method that feeds back the MRE calibrated data set to model-based OPC method. By using this method, better OPC model can be made. We will be presenting the result after the method has been applied on sub-60nm device and the capability of this method.
In recent years, more burden is placed on OPC(Optical Proximity effect Correction) and ORC(Optical Rule Check) like never before due to low process margin caused by adoption of "Low K1" technology on lithography process. Normally, chip is composed of cell, core and periphery regions. Each of these regions has different characteristics patterning wise but usually the region with high density has much more chance for pinch, bridge or killing error and also has small process window. So verification of OPCed data must be highly accurate with fast operation speed. In this paper we developed full chip based ORC(Optical Rule Check)which satisfies both need, accuracy and speed. The result of pinch, bridge and small process window verification of Hybrid ORC will be shown followed by comparison of rule and model ORC methods.
As the pattern size becomes smaller, double or multi exposure is required unless the epochal solutions for overcoming the limits of present lithography system do appear or are discovered. ArF DET (double exposure technology) strategy based on manual OPC with in-house simulation tool, HOST (Hynix OPC simulation tool), is suggested as a possible exposure method to extend the limitation of current lithography. HOST requires no additional procedures and separate layout optimizations of each region in terms of OPC are enough. Furthermore, it is possible to change illumination condition of each region and the overlap between two regions with ease. The results from the simulation are pattern size and profile of each condition according to the defous and misregistration. 0.63 NA ArF Scanner and Clariant resist is used for wafer process. The resist was coated on Clariant organic BARC using 0.24 um thickness. Dipole illumination for cell region and annular illumination for peripheral region are used. Cell region contains 0.20 um pitch duty pattern and peripheral region 0.24 um pitch duty pattern. The boundary of two regions is investigated in view of validity of stitching itself. The layout of reticles used as the cell and peripheral region are optimized by OPC, respectively and then, additional OPC was treated to the boundary, i.e., stitching area to compensate the cross term of the boundary caused by separate and independent optimization with OPC in the cell and the peripheral regime. The final patterns were acquired by defining the cell at first and the peripheral region secondly with different defocus and registration in respect to the cell. The actual data on wafer are presented according to defocus and one region's overlay offset relatively to the other region. And the outstanding matching between simulation results and in-line data are shown. Lithography process window for stable patterning is thoroughly investigated in view of depth of focus, energy latitude, registration between two stitched regions and stitching itself in the boundary. It is found from the experiment that total DOF of DE (double exposure) is 0.5 um and the total EL of DE is 10.0% in this paper. At present, it is very difficult to ensure stable process margin for the sub-0.10 um patterning. But there is a promising technology called stitching with special optimization. In addition, this technology will be nominated as an eternal candidate process whenever our lithography is in the adversity at the limits of his days.
Recently, the miniaturization of the design rule pushes the pattern sizes in the peripheral region as well as cell region to the resolution limit of exposure tools. Therefore it is necessary to apply optical proximity correction (OPC) not only to the patterns in cell region but also to those in peripheral region. It is impossible to apply manual OPC method in peripheral region. Because the peripheral region is composed of random patterns with large data volume, and it takes too long execution time with manual OPC. For random pattern OPC in peripheral region, automatic OPC tool is required. Now for the automatic OPC tool, model-based and rule-based methods are developed for the commercial use. In this paper, the effectively applicable process is discussed using model-based method in automatic OPC at the sub-0.10 micrometer design rule in ArF lithography. For the application of automatic OPC tool at the design rule of sub-0.10 micrometer and ArF process in memory devices the following problem should be cleared. In small size of design rule, we should consider not only pattern fidelity but also process margin such as depth of focus (DOF) and exposure latitude (EL) at the cell OPC. But automatic OPC tool is insufficient to be applied for cell region OPC, because it considers not process margin but pattern fidelity and it has low accuracy using much approximation model to reduce layout correction time. To solve this problem, we suggest a full chip OPC process using both automatic OPC tool and the manual OPC method using the novel lithography simulation model (Diffused Aerial Image Model, DAIM). DAIM is available to predict wafer pattern and process margin of cell, its accuracy is verified in ArF process as in KrF process. We could see small standard deviation error between experiment and DAIM in ArF process using various line or space patterns, which is about 9 nm at binary intensity mask (BIM). So the manual OPC with DAIM resulted in the wide process margin and good pattern fidelity overcoming the limitation of automatic OPC tool. However it is necessary to correlate energy level of DAIM for cell region OPC with that of the model in the automatic OPC tool for peripheral region OPC, because cell and peripheral region are exposed with the same exposure dose in stepper or scanner. In case of ArF process, we could see the small difference of energy level and standard deviation error, which is about 1.4%, 2 nm at BIM and 6.3%, 3 nm at half-tone phase shift mask (PSM), between DAIM and automatic OPC tool. As the result of using DAIM and automatic OPC tool simultaneously at full chip OPC, we could see improved results from cell to peripheral region at the sub-0.10 micrometer design rule in ArF lithography.
The patterning potentialities of sub-100nm pattern for ArF lithography was evaluated with conventional alternating PSM (alt-PSM) for dense lines and spaces (L/S) and phase edge PSM (PE-PSM) for isolated lines of memory device. In dense L/S pattern,110nm pattern was defined with relatively small depth of focus(DOF) window(~ 0.2 ?m) due to phase error of mask. As pattern sizes was changed from 130nm to 200nm, critical dimension (CD) difference between two neighboring spaces was varied and it was assumed that micro loading effect was occurred in Qz etching. The linearity was guaranteed to dense L/S of 110nm and isolated line of 90nm, and Iso-Dense bias was controlled within 15nm. The 60nm and 70nm isolated lines of PE-PSM ware defined with good process windows in the case of OA_X size(X-direction size of Cr open area) of 0.5 ?m. The 55nm isolated line was also defined. The pattern shift of isolated lines was occurred with 4~7nm as phase of mask was varies within 190 ~ 200 ° . Though the alt-PSM with high numerical aperture (NA) for ArF lithography was strong candidates for sub-1 OOnm lithography of memory device, the issues of mask fabrication such as tighter phase control and minimizing etch loading effect would be big obstacles. On the contrary, there were many possibilities of sub-100nm patterning in PE-PSM with good process windows, however tighter control of pattern shift due to phase error must be studied intensively.
Recently, the miniaturization of the design rule of memory devices pushes the minimum feature sizes down to sub- wavelengths of the exposure tools. The design of a memory device comprises not only the dense patterns with critical small size in the cell region but also the random patterns in the peripheral region; the latter also need sub- wavelength lithography technology as well as the former. And the optical proximity correction (OPC) has been strongly required for the random patterns in the peripheral region where the same energy is exposed as in the cell region. Therefore, the high accuracy of simulation model used in the OPC is necessary for the full chip OPC tools. However traditional aerial image simulation has a limitation to the application due to its lack of accuracy because it does not take into account a resist process. We introduced novel lithography simulation model in 1998, which describes resist process by diffusion and chemically amplification function.
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