Apparatus for measuring thickness of a substrate

Abstract

An apparatus for measuring thickness is provided. A light source irradiates a front surface or a rear surface of a substrate with a light. A splitter splits the light into a reference light and a measurement light. The reference light is reflected by a reference light reflecting device. An optical path changing device changes an optical path length of light reflected from the reference light reflecting device. A light receiving device measures an interference of the reflected light from the substrate and the reference light from the reference light reflecting device. A thickness of at least one of the front surface, rear surface or inside of the substrate is measured based on a measurement of the interference.

1 . An apparatus for measuring thickness, comprising:
 light source means for irradiating a front surface or a rear surface of a substrate with a light;   a splitter that splits the light into a reference light and a measurement light;   reference light reflecting means for reflecting the reference light;   optical path changing means for changing an optical path length of light reflected from the reference light reflecting means; and   light receiving means for measuring an interference of the reflected light from the substrate and the reference light from the reference light reflecting means,   wherein a thickness of at least one of the front surface, rear surface or inside of the substrate is measured based on a measurement of the interference;   wherein the light source means comprises:
 one light source or two light sources having different wavelengths that measure the temperature or thickness of the substrate; and 
 a displacement-measuring light source that measures the displacement in the optical path changing means; and 
   wherein the light receiving means comprises:
 one or two light-receiving devices corresponding to the one or two light sources that receive the interference light based on the light from the one or two light sources that has been reflected from the substrate and the reference light reflecting means; and 
   a displacement-measuring light-receiving device that receives the interference light based on the light from the displacement-measuring light source that has been reflected from the substrate and the reference light reflecting means.   
   
   
       2 . An apparatus for measuring thickness according to  claim 1 , wherein the light source for measuring the thickness of the substrate has a wavelength of 0.3-20 μm, and a coherence length of 0.1-100 μm. 
   
   
       3 . An apparatus for measuring thickness according to  claim 1 , wherein the light source means comprises two light sources, one of which has a wavelength providing a relatively large temperature coefficient of change in refractive index of the substrate, and the other of which has a wavelength providing a relatively small coefficient of temperature change in the refractive index of the substrate.