Three-dimensional step–height measurement using sinusoidal wavelength scanning interferometer with four-step phase-shift method

Abstract

A sinusoidal wavelength scanning interferometer with the four-step phase-shift method is demonstrated for a three-dimensional profile measurement. The interference phase-shift signal generated by the sinusoidal wavelength scanning contains information about optical path difference covering a nm-μm scale structure. The interference phase-shift signal was obtained by the four-step phase-shifting method. The sinusoidal wavelength shifting with a frequency of approximately 180 Hz and tunable range of 5.7 nm was performed by the Littman–Metcalf external resonator-type tunable laser with a center of 772.1 nm. The full-field surface profile measurement was conducted by a charge coupled device image sensor with an accuracy on a nm scale. The surface profiles of gauge blocks with a step height up to about 10 μm were successfully measured with a surface profile irregularity of 3.8×10−2 μm. The deviations of two measured surfaces of upper and lower steps were estimated to be 1.6×10−2 μm and 3.1×10−2 μm, respectively.