Cr atom lithography grating and wavelet-based phase demodulation self-mixing interferometer for traceable nanoscale displacement metrology

Abstract

High-precision nanoscale displacement measurements are crucial in semiconductor manufacturing, nanotechnology, and ultra-precision machining. The Laser Self-Mixing Grating Interferometer (SMGI) has gained widespread adoption due to its compact design, low cost, and high precision. However, its precision has been constrained by limitations in grating performance and phase resolution methods. In this study, we propose a novel SMGI system incorporating a chromium (Cr) atom lithography grating with a high line density of 4700 lines/mm, achieving picometer-level pitch accuracy. This advancement significantly enhances measurement precision. Furthermore, we introduce a Continuous Wavelet & Hilbert Transform (CWHT) algorithm to improve robustness in direction discrimination and phase resolution. Experimental results demonstrate that the system achieves an expanded uncertainty (k = 2) of 7.8 nm within a 20 μm range. This proposed system offers a compact (optical path dimensions: 49 mm × 49 mm × 20 mm), traceable, and high-precision displacement measurement solution for ultra-precision manufacturing, while also introducing an innovative signal processing approach for self-mixing interferometry. These advancements could advance nanoscale displacement measurement technology and may provide a practical solution for high-precision industrial applications.