Measurement of absolute optical thickness of a semiconductor mask glass by wavelength scanning interferometry

Abstract

Measurements of the surface shape and optical thickness of a semiconductor mask glass by Fizeau interferometer suffer from an overlapping of several interference fringes, which makes the phase measurement difficult. Wavelength scanning interferometry can separate these fringes in the frequency space. The absolute optical thickness of a 7-inch square mask glass was measured by a phase-shift Fizeau interferometer in a 633 nm wavelength region.