Film thickness measuring apparatus using interference and film thickness measuring method using interference

A film thickness measuring apparatus using interference, comprising:

• a placement unit on which a substrate is placed, the substrate having a transparent film formed on its front surface;
• a light source that emits light to the substrate placed on the placement unit;
• a half mirror that divides the light from the light source to be emitted to the front surface of the substrate and to a reference plane, and that overlay reflected light from the front surface of the substrate and reflected light from the reference plane to form interfering light;
• an optical filter with which an intensity spectrum of transmitted light exhibits a plurality of peaks, the optical filter being disposed between the light source and the half mirror;
• an imager that images the interfering light;
• and
• an arithmetic unit that calculates a film thickness of the transparent film based on an imaging result obtained by the imager.