| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure a plate thickness even when an object to be measured is inclined. SOLUTION: An optical sensor 10A receives an interference wave of a light beam f3A reflected on a reference face 5A and a light beam f4A reflected on the surface of a semiconductor wafer 50, and a signal is output in accordance therewith. An optical sensor 10B receives an interference wave of a light beam f3B reflected on a reference face 5B and a light beam f4B reflected on the rear face of the semiconductor wafer 50, and a signal is output in accordance therewith. A plate thickness measuring circuit 30 detects the positions of the surface and the rear face of the semiconductor wafer 50 in accordance with these signals to measure the plate thickness. Optical sensors 13A, 16A separate and receive a part of the light beam f4A at respectively separated positions, and signals indicating the positions of respective light axes are output. The plate thickness measuring circuit 30 calculates the inclined angle θof the semiconductor wafer 50 on the basis of the signals from the optical sensors 13A, 16A, it is substituted for tan2 (θ/2), and the accurate plate thickness of the semiconductor wafer 50 is measured by subtracting it from a previously found plate thickness. |
