| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to decide a replacement time of an optical fiber correctly. SOLUTION: During measurement of etching depth, light from a light source 34 is conducted through an optical source optical fiber 35 and irradiated on an etching substrate 5 in the etching chamber 1. The reflected light from the etching substrate 5 is passed through a detecting optical fiber 36 and a spectroscope 37 and the etching depth is measured by a depth processing unit 38. When the deterioration of the optical fiber in ages is tested, a reflective body is mounted between the etching chamber and both optical fibers, and the reflected light from the reflective body is separated by the spectroscope into waveforms, such as a waveform with transmission coefficient decreasing as the optical fiber deteriorates in ages, and a waveform with a transmission coefficient without a decrease, regardless of the deterioration of the optical fiber. The replacement time of the optical fiber by deterioration is decided from the intensity of two separated waveforms and decision values of replacement.
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