System for detecting minute particles on or above a substrate

摘要

A fine-particle measuring apparatus designed to measure fine particles attached to the surface of a substrate for a semiconductor device set in a processing unit for formation of films, etching, cleaning, etc. and fine particles suspended in the space above the substrate surface by the use of scattering of a laser beam caused by these fine particles. The measuring apparatus comprises a laser beam scanning mechanism for irradiating a measuring space with a laser beam the angular position of which is minutely modulated at a predetermined frequency, a photodetector which receives light scattered by a fine particle and converts the received light into an electrical signal, and a signal processor which extracts from the electrical signal output by the photodetector a signal component whose frequency is the same as or double that of a modulating signal for the minute scanning with the laser beam and which has a constant phase difference in terms of time with respect to the modulating signal. Thus, it is possible to measure fine particles with high sensitivity without substantially disturbing the environment inside the process unit or the process itself.