PURPOSE: To accurately measure a thickness of a workpiece by directly measur ing the thickness of the workpiece at the time of polishing by a second displace ment sensor via an arm member.
CONSTITUTION: Each time a wafer A is moved to a position of a measuring through hole 12 at the time of polishing the wafer A, a distance to a surface of the wafer A is measured by a first displacement sensor 17, and this measured distance is input to a controller. If the distance is not a predetermined distance α, a drive signal is so output to a pulse motor 19 as to become the distance α., and a cylindrical holder 15 is rotated. Thus, when the holder 15, i.e., a cylindrical support 16 is vertically moved, an arm member 20 held at its outer end is also moved vertically, and hence the vertically moving distance, i.e., the displacement of the member 20 is detected by a second displacement sensor 22, and its displacement amount is input to the controller, and a polished amount of the wafer A is obtained.
ISOBE MITSUHIDE
YAMASHIRO TOSHIRO
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