Patent ID: 7542148

Claim:
A method for measuring a physical quantity of a measurement object in a substrate processing apparatus using a physical quantity measuring apparatus, said physical quantity measuring apparatus including a light receiving device that receives first reflected light of light irradiated on the measurement object and second reflected light of light irradiated on a movable reflection device, a movement control device that causes the movable reflection device to move so as to cause interference to occur between the first reflected light and the second reflected light, and a physical quantity calculation device that calculates a predetermined physical quantity of the measurement object based on a position of the movable reflection device in which the interference occurs, said method comprising the steps of: (a) calculating a first interference position-related value that is related to a position of the movable reflection device in which interference occurs between the first reflected light and the second reflected light as the movable reflection device is caused to move in a first direction; (b) calculating a second interference position-related value that is related to a position of the movable reflection device in which interference occurs between the first reflected light and the second reflected light as the movable reflection device is caused to move in a second direction that is opposite to the first direction; and (c) calculating an average value of the first and second interference position-related values.