Optimization of Pupil Fit Parameters for Contact Hole Pattern CD Difference Improvement

In the stacked semiconductor structure, the contact hole layer is widely used in Dram/3D NAND as a connection path between layers. During the lithographical process of the contact hole layer, a critical issue known as CD difference appears. When faced with this issue in a mass production environment, solutions are limited. In particular, the only solution for the issue caused by a difference of pupil shape is to change the illumination ID, which requires a full design change of the pupil. This is challenging and causes differences in the recipe and equipment. As a way to fundamentally solve this problem, the ellipticity among the pupil fit parameters is optimized to minimize CD differences. Through simulation, the difference between the issue pupil and the reference pupil was confirmed, and the pupil fit parameter was calculated. The pupil shape was predicted by applying the calculated pupil fit parameter. Pattern simulation was performed using the predicted pupil shape, and conditions suitable for the direction of improvement were established to confirm improved CD difference. In both cases, the improvement tendency was confirmed in the predicted direction and was suitable for a mass production environment.