Fine-particle measuring apparatus

Abstract

A fine-particle measuring apparatus designed to measure fine particles attached to the surface of a substrate of 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 light phase modulator for generating two laser beams which have the same wavelength and the phase difference between which is modulated at a predetermined frequency, an optical system which causes the two laser beams to intersect each other within a space containing the fine particles being the objects of measurement, a photodetector which receives light scattered by any of the fine particles in the region which the two laser beams intersect, and converts the received light into an electrical signal, and a signal processor which extracts from the electrical signal based on the scattered light of a signal component whose frequency is the same as or double that of a phase modulating signal for the modulation effected in the laser beam phase modulator and which has a constant phase difference with respect to the phase modulating signal. Thus, it is possible to measure fine particles with high spatial resolving power without substantially disturbing the environment inside the process unit or the process itself.