Wafer alignment measurement using vortex beam interferometry and double diffraction by the same grating

High-performance wafer alignment is a cornerstone of the stringent overlay accuracy required in integrated circuit manufacturing. However, conventional alignment techniques often struggle with process-induced variations and signal noise. Building on phase grating alignment, we present a method that combines double diffraction by the same grating with vortex beam interferometry. Our approach incorporates two main advances. First, a double-pass optical configuration causes the diffracted beams to interact with the alignment mark twice, thereby enhancing the displacement-induced phase difference. Second, by exploiting the interference of conjugate vortex beams, the measurement of a microscopic phase change is converted into the measurement of a macroscopic rotation angle of the interference pattern, providing inherent immunity to common mode noise. We experimentally validated the concept and achieved a strong linear response (R² > 0.998) and a measurement repeatability better than 1.1 nm (1σ). The proposed technique offers a route for high accuracy wafer alignment and shows strong potential for applications in DUV and EUV lithography systems.