High Precision Double-Interferometry for Large Step-Height On-Line Measurement Using Waveform Transforming Technology

Abstract

This paper focuses on obtaining high measurement precision for large step-height by double-interferometry using waveform transforming technology. The interferometer performing the measurement, which is stabilized by a feedback loop and is robust enough for on-line measurement, works simultaneously in both modes of single-wavelength interferometry (SWI) and two-wavelength interferoemetry (TWI). In order to make the peak point of the TWI signal prominent and unique, the cosine-amplitude-modulated TWI signal has been transformed to be a triangular signal with the same frequency as the cosine-amplitude modulating and being in phase with it. The positions of the one-to-one corresponding peaks of the TWI signal and the triangular signal are the same. As the peak point of the triangular signal can be addressed much more precisely than that of the TWI signal, by employing the shifting range of the peak of the triangular signal instead of that of the TWI signal to determine the amplitude of the step height while using the SWI signal to measure the value of it, the system could measure the height with high precision. The standard deviation of measuring a gauge block with the height of 0.5mm is 0.8nm.