There is here disclosed a semiconductor device manufacturing method, comprising arranging at least one subject piece in a processing chamber, and starting a predetermined processing, applying a light having a predetermined wavelength to a monitoring section which is formed to enable transmission and reflection of the light and which is provided at a tip of a monitoring device to indirectly monitor a thickness of a film on the subject piece, and measuring a reflection light which is the application light is reflected near the monitoring section, while the light and the reflection light are isolated from an atmosphere and a substance in the chamber, measuring an amount of a substance on the monitoring section based on the reflection light, determining a thickness of a film on the subject piece based on the substance, and conducting the processing while controlling the processing based on the thickness of the film.
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