| 摘要 |
PROBLEM TO BE SOLVED: To highly accurately efficiently measure variation in the thickness of a thin plate material such as a wafer by irradiating the surface of a thin plate material with measuring light, receiving the reflected measuring light, and measuring displacements in the surface of the thin plate material. SOLUTION: Mixed light L0+L1 outputted form a polarization beam splitter 34 is converted into parallel light by a collimator lens 54 via a plurality of mirrors 52, converged onto the light receiving surface of a light receiving part 50 by a focus lens 56, and reliably inputted to the light receiving surface while inclination and displacements caused by the reflection of measuring light at the surface of a wafer W. A light signal is converted into an electric signal at the light receiving part 50 to analyze the waveforms and phases of reference light L0 and measuring light L1. By subjecting data to computation processing, it is possible to obtain the surface location of the wafer W or its changes as numerical information. By performing measurements at different locations along the surface of the wafer W, it is possible to obtain fluctuations i.e., displacements in the surface location of the wafer W due to a locational.
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