Optical heterodyne surface profiling interferometer with automatic focusing

Abstract

In modern semiconductor and optics industries, there is a strong demand for a highly sensitive and non-contact surface profilometer. This paper describes an optical heterodyne surface profiling interferometer with automatic focusing which has been developed recently. The essential feature of the profilometer is a newly designed common-path method to minimizes the effects of environmental conditions. A powerful signal processing scheme is also developed, which includes three parts: automatic voltage control, phase measurement and automatic focusing control. All these make the repeatability and stability of the profiling interferometer greatly improved. The height resolution is 3.5nm and lateral resolution is 0.4μm Experiments show that the profiling interferometer is suitable for on-line use.