A common-path fast-scanning interferometer system for thin-film surface profiling

A common-path fast-scanning interferometer system has been developed to measure a thin-film surface profile. To get thin-film profiling with the resolution of approximately 10 nm, a He–Ne laser with the wavelength of 633 nm has been chosen as a beam source. To cancel out any path difference arising from the vibration of the target at such a short wavelength, a common-path design has been implemented for the interferometer. Combination of a rotating mirror and a cylindrical lens has been used to scan a surface with high speed by aiming probing beams at different positions. For more accurate measurements, a heterodyne detection technique has been adopted in this system. A prototype apparatus of the common-path fast-scanning heterodyne interferometer system has been assembled and tested for a surface profiling of an indium tin oxide coated glass plate, demonstrating thin-film profiling with the resolution of 30 nm.