Chromatic confocal coherence scanning interferometry with speed-variable scanning method to measure large-depth step

Abstract

Coherence scanning interferometry (CSI) is a crucial measurement technique for achieving non-contact, rapid, and high-precision measurements. However, when applied to large-depth steps, CSI encounters challenges related to prolonged measurement times and suboptimal signal utilization. This paper introduces a hybrid CSI system that integrates the chromatic confocal technique (CC-CSI). The confocal spectral signal peak facilitates the rapid determination of the coherence area, allowing the scanning process to be divided into two phases. The signal collection is limited within the coherence area at a lower scanning speed, while in other positions, the scanning speed is increased. This speed-variable scanning technique significantly augments measurement efficiency. The CC-CSI system with the speed-variable scanning method demonstrated a significant enhancement in measurement time compared to conventional CSI under identical experimental conditions. The measured step heights were 100 μm, 200 μm, and 300 μm. Standard deviations of less than 0.3 μm were observed in 10 consecutive measurements. In addition, the proposed CC-CSI system demonstrated the capability to profile the groove structure.