Patent ID: 7439534

Claim:
A reflected light intensity ratio measuring device for measuring a reflected light intensity ratio of an object substrate to be treated relative to a standard substrate, comprising: a chamber for receiving the object substrate therein, said chamber permanently holding thereon a calibration standard member which is similar in surface property to the standard substrate during continuous processing of said object substrate; a substrate holding part for holding the object substrate within said chamber; a light emitting and receiving part fixed to said chamber for directing light onto a main surface of the object substrate held by said substrate holding part or onto said calibration standard member and for receiving light reflected from the main surface or from said calibration standard member, and said calibration standard member being located in an optical path of light emerging from the light emitting and receiving part, and a calculation part for calculating the reflected light intensity ratio of the object substrate to the standard substrate from the intensity of reflected light obtained when light, is directed from said light emitting and receiving part onto said calibration standard member and the intensity of reflected light obtained when light is directed onto the object substrate, said calibration standard member being placed in such a position that the light emerging from said light emitting and receiving part impinges upon the object substrate when the object substrate is held by said substrate holding part and impinges upon said calibration standard member when no object substrate is held by said substrate holding part.