| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem, where in the conventional method etching depth used to be detected by means of frequency analysis, etc., by obtaining an interference waveform using monochromatic light such as a laser beam, in the case of this interference waveform, a cyclic distortion at a specific phase cannot be avoided and the etching speed at the distorted part cyclically deviates to a great extent, so that etching depth cannot be measured or monitored accurately. SOLUTION: In the method of detecting etching depth based on the present invention, three kinds of interference lights L1, L2 and L3, having different waveforms reflected from the upper surface of surface E to be etched and surface E' to be etched on a semiconductor wafer W, are detected, and then frequency analysis of each frequency is performed to obtain frequenciesω1 (t),ω2 (t) andω3 of respective interference waveforms. Then, etching speed suitable for each interference frequency is calculated based on these frequencies, and the calculated etching speed is obtained as E1 (t), E2 (t) and E3. Subsequently, deviation of the etching speed calculated, based on the distortion of any of the interference waveforms, is averaged by the calculated etching speed of another distortionless waveform, and then the averaged etching speed Eave is integrated to calculated etching depthσ.
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