Moire-Based Absolute Interferometry With Large Measurement Range in Wafer-Mask Alignment

The moire-based interferometry is demonstrated to significantly improve the measurement range in wafer-mask alignment by adopting two specifically designed four-quadrant grating marks. These relationships between the measurement range, the moire periods and the accuracy of the moire-based detection algorithm are deduced. By demodulating the transverse shifts of the moire fringes with two kinds of periods, the final misalignment can be accurately determined. An experimental setup of the wafer-mask alignment is constructed to explore the feasibility and effectiveness of proposed approach. Results indicate that with the established configurations, the measurement range can be readily extended to 120 mu m, which is dozens of times larger than conventional methods, and meanwhile the detection accuracy retains to be at nanometers level.