New Quality Index to Improve Overlay Measurement Accuracy Based on MoiréMarks: Method for Quantifying Moiré Pattern Quality Using the Signal Shape Index

As semiconductor integrated circuits become increasingly miniaturized, overlay metrology has garnered significant attention. Moiré marks offer superior accuracy and robustness compared to conventional grating marks; however, their sensitivity to various optical system parameters can affect measurement precision. This study presents a novel quality index, termed the signal shape index, to quantitatively assess the quality of Moiré marks, which are a crucial factor in enhancing the reliability of overlay metrology. Current quality indices primarily focus on signal strength, consistency, and asymmetry; however, they inadequately capture vital information regarding the shape of Moiré patterns. To address this limitation, the comprehensive index quantifies the shape of Moiré patterns, providing a more effective evaluation of their quality. This shape-based quality index is compared with the established modulation transfer function index. The new index more accurately reflects the characteristics of Moiré patterns, thereby facilitating the optimization of optical system parameters. Implementing this novel quality index is expected to significantly improve the accuracy of Moiré mark-based overlay metrology, contributing to the stabilization and efficiency of semiconductor manufacturing processes.