The Impact of Wafer Warpage-Induced Unevenness on Alignment

Accurate alignment of patterns on different layers using alignment marks is a challenge, where poor alignment results in overlay errors or even risks wafer rejection especially when dealing with curved wafers. In this study, we utilized the finite difference time domain (FDTD) simulation to evaluate the impact of surface flatness on the quality of signals of alignment marks. Our simulation established a simplified model to reflect surface non-uniformities. The results reveal that non-uniformities can cause a decrease in diffraction signal intensity. This indicates the critical influence of surface non-uniformities on alignment quality, offering valuable implications for process optimization.