LithoExp: Explainable Two-stage CNN-based Lithographic Hotspot Detection with Layout Defect Localization

Convolutional neural networks (CNNs) successfully detect lithographic hotspots by learning from hand-designed features of layout patterns or entire layouts, as images, in an end-to-end fashion. However, compared to lithography simulation, CNN-based solutions demonstrate inferior hotspot detection accuracy and a high false-alarm rate. Moreover, the interpretability of the hotspot prediction process has yet to be considered due to the “black-box” nature of CNNs. In this work, inspired by conventional lithography simulation where defect regions are simulated as direct evidence for hotspot identification, we propose an explainable two-stage CNN-based hotspot detector that considers both the accuracy and interpretability of hotspot detection. Our architecture learns to locate the defect areas in the first stage as extracted hotspot features. In the second stage, we combine the strength of feature engineering and end-to-end learning, incorporating the original layout input, the learned defect location map from the first stage, and a fixed auxiliary region of interest (ROI) map for final hotspot detection. Experimental results for our technique exhibit the highest hotspot accuracy (98.1%) and the lowest false-alarm rate (4.0%) thus far compared to all prior CNN solutions. We also demonstrate the best overall qualitative and quantitative interpretability results with the highest increase in confidence (IC) and the lowest average drop (AD) in scores when CNN interpretation methods such as Grad-CAM-based approaches are applied. We further demonstrate use cases of our technique for successfully justifying and pinpointing hotspot mispredictions by examining the prediction evidence from our learned defect locations.