Film thickness measuring apparatus employing microprojector of spectral

Abstract

A film thickness measuring apparatus comprising an optical measuring system and an optical projecting system is disclosed. The conventional optical measuring system includes a light source, a first optical system, a monochromator, a second optical system and a photomultiplier tube andmonochromatic light is emitted from the first optical system toward the surface of the film layer on a material of which film thickness is to be measured. While reflection interference takes place between light reflected at the surface of the film layer and light reflected at the base plate, reflected light beam is transmitted to the photomultiplier tube via a semitransparent mirror so that the thickness of the film layer is measured. Before measuring of the film thickness is initiated, there is necessity for determining the correct position of the material to be measured. To this end the optical projecting system includes a third optical system adapted to emit light toward the surface of the film layer via a turnable mirror and reflected light is then transmitted to a screen via the turnable mirror so as to visually observe an image of the material in an enlarged scale. Thus, when film thickness is to be measured, the turnable mirror is caused to assume the inoperative position by turning operation.