A Defocus-Robust Encoded Pattern for Simultaneous Absolute Positioning and Parallelism Evaluation in High-Magnification Microscopy

Microscopy-based positioning techniques are applicable to precision manufacturing scenarios, such as semiconductor fabrication. High-magnification microscopic metrology (e.g., using a 100× objective) provides an extremely small pixel equivalent size, thereby offering a solid physical basis for achieving nanometer-level absolute positioning. However, the extremely shallow depth of field—typically a few hundred nanometers—makes spatially varying defocus, mainly induced by target–stage parallelism errors, a critical obstacle to robust large-range positioning. Existing encoded-pattern absolute positioning methods are therefore often demonstrated at low magnification, where defocus is less severe. This article proposes an encoded-pattern method that enables both defocus-robust absolute positioning and in situ installation parallelism evaluation under high magnification. For positioning, a sub-pixel edge-gradient scheme is used to estimate feature locations with reduced sensitivity to blur. For parallelism evaluation, the defocus-dependent blur magnitude is leveraged to quantify the target tilt. Experiments demonstrate a positioning resolution characterized by a standard deviation (STD) of 0.8 nm and a root-mean-square error (RMSE) of 115.5 nm over a 3 × 3-mm range. Moreover, the proposed in situ parallelism evaluation estimates the target tilt with a mean absolute error of 94.8 nm.