| 摘要 |
PROBLEM TO BE SOLVED: To measure the etched depth of an object to be measured with accuracy by only detecting the reflected and diffracted component of the light projected upon the object. SOLUTION: The etched depth D (t) of a silicon wafer 15 is found by receiving reflected and diffracted light Q" containing plasma light P" from the wafer 15 by means of a photodetector 18 while a pulse laser beam Q is projected upon the wafer 15 and extracting the frequency component matching the pulse oscillation frequency of a pulse laser oscillator 16, namely, the component of the reflected and diffracted light Q" from the detect signal I outputted from the photodetector 18 by means of a lock-in amplifier 19, and then, sending the extracted signal IQ to an etched-depth computing and processing section 20.
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