| 摘要 |
PURPOSE:To measure optical film thickness with high accuracy by detecting the output difference between reflected light beams by using two optical fibers where a film is formed on one end surface to a quarter wavelength on nearly the same optical paths branched by a beam splitter. CONSTITUTION:Light from a light source which is split into two by the beam splitter passes through optical fibers 2a and 6a, and 2b and 6b with nearly equal optical path length which include beam splitters 3a and 3b respectively and is reflected by according to the optical film thickness of thin films vapor- deposited on substrates 7 parallel to end surfaces 9 and 9a in a bell jar 6 and incident on photodetectors 4 and 4a through optical fibers 6a and 2e, and 6b and 2f which have nearly equal optical path length. A quarter-wavelength thin film is formed on one end surface 9a and reflected components from the end surfaces of the detectors 4 and 4c differ in phase difference by pi to obtain an output corresponding to the optical film thickness of the thin film which is amplified through the differential processing of a differential amplifier 8 for the outputs of both detectors and also remove components originating from unnecessary external light such as reflected light from the beam splitters, thereby measuring the optical film thickness with high accuracy.
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