Patent ID: 8014891

Claim:
An etching amount calculating method for calculating an etching amount of a concave portion that is formed in a substrate using a mask film by etching the substrate, comprising: an irradiating step of irradiating light on the substrate; a light receiving step of receiving superposed interference light resulting from superposition of at least interference light of reflected light from the mask film and reflected light from a bottom of the concave portion on other interference light; an interference wave calculating step of calculating a superposed interference wave from the received superposed interference light; a waveform extracting step of extracting a waveform in a predetermined time period from the superposed interference wave; a frequency analyzing step of carrying out a frequency analysis of the extracted waveform; an interference period detecting step of detecting a period of an interference wave produced from the reflected light from the mask film and the reflected light from the bottom of the concave portion from a frequency distribution obtained by the frequency analysis; an integrating and averaging step of repeating said interference wave calculating step, said waveform extracting step, said frequency analyzing step, and said interference period detecting step while shifting the predetermined time period by a predetermined time, and integrating and averaging the detected periods of the interference wave at each repetition; and an etching amount calculating step of calculating the etching amount of the concave portion based on the integrated and averaged periods of the interference wave.