An Investigation of the Influence of Light Intensity on Microscopic Imaging in Nanoscale Positioning Measurement

In vision-based measurement, light quality is the key factor of positioning precision; however, the influence mechanism of light intensity, especially on nanoscale measurements, remains unclear. This article theoretically analyzes the effect of light intensity on the image grayscale of etched topography, as well as the image grayscale distribution on the measurement uncertainty, revealing that light intensity affects the positioning measurement precision by affecting the grayscale contrast of the image. A series of validation experiments are conducted, including $10~\mu \text{m}$ repeated positioning experiments with six different light intensities and three magnifications of $5.5\times $ , $11\times $ , and $27.5\times $ . The experimental results show that the difference in light intensity produces a positioning measurement uncertainty ranging from 1.0 to 91.0 nm, which proves the high correlation between light intensity, image contrast and nanoscale positioning measurement precision. Then, this study proposes a method to find the optimal light intensity interval based on the image grayscale contrast of the etched topography, which provides a reasonable method for improving the measurement accuracy at the nanoscale. The feasibility of the method is verified by the $100~\mu \text{m}$ step-test experiments in the refined light interval under an optical microscope and industrial imaging equipment.