In recent years, curvilinear mask technology has emerged as a next-generation resolution enhancement method for photomasks, providing optimal margins by maximizing the degree of freedom in pattern design. However, this technology presents challenges in defining the layout design rule limits based solely on geometric information, such as width, space, and corner-to-corner. With the introduction of multi-beam mask writers for curvilinear pattern production, a distinct set of defects that are difficult to pre-detect by conventional mask rule check have occurred, as these cannot be explained by geometry terms alone. In this study, we propose a deep learning-based mask check method, named mask deep check (MDC) for pre-detect defects in inspection. The proposed vector graphics transformer (VGT) uses the state-of-the-art transformer architecture, drawing an analogy between the vertices of curvilinear patterns and words in natural language. We demonstrate improved performance of VGT-based MDC compared to a traditional rule-based approach and a convolutional neural network-based MDC method. Importantly, VGT exhibits robustness in recall, ensuring that defective patterns are not misclassified as normal, thereby preventing missed defects. Moreover, by employing attention maps to visualize VGT results, we gain explainability and reveal that mask defects may arise from issues related to the fabrication of specific designs, rather than being solely attributable to geometric features. VGT-based MDC contributes to a better understanding of the challenges associated with curvilinear mask technology and offers an effective solution for detecting mask defects.
Pattern selection for OPC (Optical Proximity Correction) model calibration is crucial for high-quality OPC results and low edge placement error (EPE) error in semiconductor fabrication. Pattern coverage check is also desired with the value to identify potential anomaly before mask tape out for monitoring and repair. This study evaluates pattern diversity based selection and pattern coverage check for Extreme Ultraviolet (EUV) C/H mask layers. Pattern diversity based selection has the advantage of incorporating information related to lithographic contrast and illumination effects, offering a more nuanced representation of patterns in a lithographic context. Using unsupervised machine learning, we analyze the lithographic pattern representations from sample designs and select out pattern representatives for OPC model. The study concludes pattern selection and coverage check can enhance model prediction performance for the OPC applications.
As semiconductor process technology needs to be advanced, the difficulty of patterning increases and unexpected pattern defects occur. In fact, it is very important to quickly identify and resolve these pattern defects in advance, but there is a limit to measuring all of these pattern defects that occur in wafers. In particular, in order to overcome metrological limitations, it may be best to extract actual potential pattern defects by classifying various types of patterns that actually exist. We measured how to classify weak patterns by sampling them based on previously known weak pattern group libraries, simulation-based weak patterns, and unique patterns. Through this method, engineers can subjectively judge how to find weak patterns, and it can be difficult because there is a possibility that the probability of weak patterns is low depending on the limited measurement capacity. In this paper, unsupervised learning is used to cluster and classify by pattern type based on the various features of pattern. Then, based on reliable wafer data for various classified pattern types, the degree of vulnerability to defect was quantified for each classified cluster to give a ranking for extracting a weak pattern group for each cluster, and the weak pattern was extracted based on this to confirm a high weak pattern detection rate. In addition, it provides effective solutions to extract weak patterns from various databases (DBs) and specifically to give reliability to visualization methods.
In recent years, Curvilinear Mask technology has emerged as a next-generation resolution enhancement method for photomasks, providing optimal margins by maximizing the degree of freedom in pattern design. However, this technology presents challenges in defining layout design rule limit based solely on geometric information rules based solely on geometric information such as width, space, and corner-to-corner. With the introduction of Multi Beam Mask Writers for Curvilinear pattern production, brand-new violations of Mask Rule Check(MRC) have occurred, which cannot be explained by geometry terms alone. In this study we propose a deep learning-based method for detecting MRC violations using the state-of-the-art Transformer architecture, drawing an analogy between the vertices of curvilinear patterns and words in natural language. The proposed MRC binary classifier demonstrates improved performance compared to traditional rule-based MRC and CNN-based MRC methods. Importantly, our method exhibits robustness in recall, ensuring that defective patterns are not misclassified as normal, preventing missed defects. Moreover, by employing attention maps to visualize deep learning results, we gain explainability and reveal that MRC violations may arise from issues related to the fabrication of specific designs, rather than being solely attributable to geometric features. This insight contributes to a better understanding of the challenges associated with Curvilinear Mask technology and offers an effective solution for detecting MRC violations.
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