Acta Optica Sinica, Volume. 43, Issue 23, 2315001(2023)
Lithography Hotspot Detection Based on Improved YOLOv3
The ever-shrinking feature size of integrated circuits aggravates the subwavelength lithography gap, causing unwanted shape deformations of printed layout patterns. Although various resolution enhancement techniques (RETs) used to improve wafer printability are used to improve the imaging fidelity, certain layout regions may still be susceptible to the lithography process with pinching and bridging hotspots that may produce open or short circuits. Therefore, the identification of lithography hotspots is particularly important in physical verification. In this study, we propose a hotspot detection method to improve the precision and recall of pinching- and bridging-type areas by embedding squeeze-and-excitation networks (SENets) into a pretrained YOLOv3 model. We also address hotspot and non-hotspot data imbalances by data augmentation from a lithographic perspective. Experimental results on the 2012 International Conference on Computer-Aided Design (ICCAD 2012) dataset verify the merits of the proposed deep learning-based network.
YOLOv3 uses a single network to generate candidate regions within which the locations and classifications of objects are detected and identified. The training of YOLOv3 is more effective with a single network structure. SENet is an attention mechanism that focuses on the channel features. SENet provides information regarding the importance of each channel in the feature map, enabling the network to focus on important channels while suppressing less important channels. To better distinguish lithographic hotspots from non-hotspots, SENet was embedded in the YOLOv3 network architecture to improve the representation ability between different channels in the feature map. The structure of the improved YOLOv3 is shown in Fig. 4, where SENet is enclosed in the dotted box. Imbalanced datasets cause the network to focus more on learning the features of non-hotspots, thereby reducing the performance of hotspot detection. Considering the symmetry and light source in the lithography process, a change in the direction of the layout pattern does not alter its properties, and the number of layout patterns can be increased by flipping the original layout pattern. Fig. 5 shows the flipping data augmentation method.
In this study, the effectiveness of the lithographic hotspot detection task was verified by comparing the improved and the original YOLOv3 structures. In the experiments, the intersection over union threshold is set to
Lithographic hotspot detection is a key step in the physical verification process of very large-scale integration circuit (VLSI). The pattern on the wafer is easily affected by lithographic printing, and a sensitive layout pattern produces unwanted hotspots. The geometries of hotspots and non-hotspots are extremely similar, exacerbating overfitting in deep learning-based approaches. In this study, embedding the SENet in the YOLOv3 network can focus the network on important channels in hotspot and non-hotspot feature maps. By taking advantage of the symmetry of lithography imaging, the problem of data imbalance can be addressed by flipping the hotspot samples. In the ICCAD 2012 dataset, benchmark 1 was pretrained, whose training parameters were used as the initial weights of benchmarks 2 to 6 to accelerate the training speed and improve the performance of the network. The test results show that the average recall of the proposed method is
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Mu Lin, Fanwenqing Zeng, Xiaoxuan Liu, Fencheng Li, Jun Luo, Yijiang Shen. Lithography Hotspot Detection Based on Improved YOLOv3[J]. Acta Optica Sinica, 2023, 43(23): 2315001
Category: Machine Vision
Received: May. 5, 2023
Accepted: Aug. 29, 2023
Published Online: Dec. 8, 2023
The Author Email: Shen Yijiang (yjshen@gdut.edu.cn)