Etching apparatus and etching method and detecting apparatus of film thickness

An etching method, comprising:

• a first step of receiving light of a plurality of wavelengths emitted from an object to be etched and outputting signals corresponding to respective intensities of the received light during etching of said object;
• a second step of determining a measured thickness of the object to be etched based on the output signals;
• and
• a third step of comparing the determined measured thickness of the object to be etched with a stored threshold thickness value to determine an endpoint of the etching,
• wherein in the second step, a change rate is obtained based on a calculated light quantity value obtained by smoothing operation of an output signal associated with each said wavelength at each time instant of a predetermined sampling time, and a reference light quantity value determined from the calculated light quantity value in a reference time prior to the sampling time,
• wherein a corrected light quantity value is obtained for each said wavelength based on the output signal associated with said wavelength at each time instant of the sampling time and the change rate, and
• wherein thickness of the object to be etched in the sampling time is determined based on the corrected light quantity value.