Wafer alignment measurement in lithography systems based on vortex beam interference

Overlay accuracy is a core performance metric for lithography systems. To achieve high overlay accuracy during integrated circuit manufacturing, high-performance wafer alignment is a critical enabling technology. Developing rapid and high-precision wafer alignment techniques is therefore of paramount importance. While alignment schemes based on phase grating can achieve high-precision alignment measurement, as demonstrated by ASML's series of alignment technologies that meet the requirements for immersion, EUV, and even high-NA EUV lithography, this paper proposes an alternative optical measurement scheme based on vortex beam interferometry for high-precision wafer alignment. The approach converts the ±1st diffraction orders from a grating into vortex beams with opposite topological charges. The lateral displacement of the grating is linearly transduced into the rotation of a resulting petal-like interference pattern. We established a theoretical model for this displacement-to-angle conversion and experimentally validated its performance. Under simple laboratory conditions, the measured displacement showed a coefficient of determination (R²) exceeding 0.999 for a linear fit over a 1 μm range, and a measurement repeatability (standard deviation) better than 1.8 nm. This work offers a precise solution for real-time position sensing with significant potential for DUV and EUV lithography wafer alignment.