Comparative investigation on the performance of spot positioning sensors in point-autofocus microscopy

Abstract

As products evolve towards greater precision and intelligence, their components also develop towards miniaturisation and increasing complexity. In the era of intelligence, the demand for complex small components continues to grow. The point-autofocus microscopy (PAM), with its attributes such as small measurement spots and high vertical resolution, holds a comprehensive advantage in instruments for measuring the geometry of complex small components. The performance of the spot positioning sensor directly determines the capability of the PAM to measure complex small components. This study introduces the basic measurement principles of the PAM and commonly used spot positioning sensors. The analysis explored the feasibility of applying different sensors to the PAM. An automatic segmentation and weighted localisation algorithm of the spot based on the centroid method was proposed. Using this algorithm, the spot positioning error of the complementary metal–oxide–semiconductor (CMOS) sensor can be controlled within 0.48 μm, with a measurement uncertainty of no more than ±0.19 μm. This study focuses on comparing the performance of CMOS and position-sensitive detector sensors with the performance of seven indicators. In addition, a measurement system of the PAM was constructed, and measurements of the test object were conducted using both types of sensors. The experimental results show that when the measurement system employs the CMOS sensor, it achieves higher measurement accuracy. The maximum measurement error was approximately 0.22 μm, with a measurement uncertainty of no more than ±0.10 μm.