Nanometer precision height gauge for small holes with high aspect ratio

Abstract

The demand for measuring the feature size of small holes is increasing. In this study, a nanometer precision height gauge for small holes with a high aspect ratio was developed. The height gauge comprises a Michelson interferometer, a moving and weight balance system, a tactile probing system, and a positioning control system. The errors due to the angular deflection of the moving stage were analyzed, and a corner-cube-based interferometer was designed. The structural design of the moving and weight balance systems was explored. A tactile micro/nano-probing system was developed and used. The signal processing, positioning control and measurement strategy, and software were developed. The system was calibrated and verified by testing the reference ring gauge. The experimental results show that the height gauge can achieve a resolution of 5 nm, a measurement uncertainty of 90 nm (k = 2), and a measuring range of 30 mm. The prototype can be used to measure the depth of small holes with a high aspect ratio.