| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a light beam sometimes can not be photodetected accurately owing to refraction or irregular reflection by liquid such as washing liquid and pure water used for the polishing and grinding of a semiconductor wafer since a method for reflecting a laser light beam, etc., and photodetecting its reflected light is implemented in the air as a method for confirming whether or not the wafer is mounted horizontally. SOLUTION: This method uses a measurement base, a recessed part having an opening part in a horizontal state provided to the measurement base, a liquid supply means which continuously supplies liquid to the recessed part, a light beam irradiation part provided to the recessed part, and a light beam photodetection part provided to the recessed part and the liquid supply means continuously supplies liquid which is much enough to maintain its surface tension to the recessed part of the measurement base; while a plate body is mounted on the liquid, the plate body is irradiated with and reflects the light beam from the light beam irradiation part and the light beam photodetection part receives the reflected light beam.
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