Importance

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Abstract

In a phase interference detecting system with use of an interferometer, a height from a reference surface on a measurement surface is detected by receiving interference components of reflection lights from the reference surface and a measurement surface, which lights are divided from a laser beam and are modulated with a frequency being different therefrom, i.e., by irradiating only one laser beam. A light detector is constructed with a line type sensor for receiving the interference components of the reflection lights, and has a plurality of pixel groups for common use of a measurement surface and a plurality of pixel groups for exclusive use of a reference surface, which are provided at both thereof. A reference surface phase detecting means calculates a reference surface phase signal with respect to the pixels at a measurement point within the pixel group for common use of measurement surface, on a basis of an average value of signals of a predetermined number of pixel groups positioned at both sides in symmetric with respect to said measurement point. A measurement point phase calculating means calculates a measurement point phase signal of said reflection lights being incident upon the pixels at said measurement point on a basis of signals of the pixels at said measurement point. A height calculating means calculates out a signal corresponding to height of said measurement point by subtracting said reference surface phase signal from said measurement point phase signal.

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First Claim