Patent ID: 8670128
Filing Date: 2014-03-11
Classification: G01B

Abstract:
1. A profile measuring apparatus used for scanning front and back surfaces of a workpiece and measuring a thickness distribution of the workpiece in a non-contact manner, comprising: first optical branching means for branching a source light that is emitted from a predetermined light source into two lights; optical guiding means for guiding the branched lights by the first optical branching means in directions toward measurement portions on the front and back surfaces of the workpiece, the measurement portions facing each other; second optical branching means for further branching each of the branched lights of the source light guided in the directions toward the measurement portions on each of front and back of the workpiece into two lights; optical modulating means for modulating a frequency or frequencies of one of or both the branched lights by the second optical branching means at each of the front and back of the workpiece, and generating two measurement lights with different frequencies; two heterodyne interferometers that irradiate the measurement portion with one of the measurement lights, and causes an object light, which is the one of the measurement lights reflected by the measurement portion, to interfere with a reference light, which is the other of the measurement lights, at each of the front and back of the workpiece; third optical branching means for branching each of the two measurement lights into two lights including a main light, which is input to the heterodyne interferometer, and a sub-light, which is other than the main light, at each of the front and back of the workpiece; sub-light interfering means for causing the two sub-lights branched by the third optical branching means to interfere with each other, at each of the front and back of the workpiece; measurement optical system holding means for integrally holding a measurement optical system including the second optical branching means, the optical modulating means, the heterodyne interferometers, the third optical branching means, and the sub-light interfering means, at each of the front and back of the workpiece; measurement light intensity detecting means for receiving interfering lights obtained by the two heterodyne interferometers and outputting intensity signals of the interfering lights; reference light intensity detecting means for receiving an interfering light obtained by the sub-light interfering means and outputting an intensity signal of the interfering light, at each of the front and back of the workpiece; and phase information detecting means for detecting phases of two beat signals including an output signal of the measurement light intensity detecting means and an output signal of the reference light intensity detecting means, and detecting a phase difference between the two beat signals, at each of the front and back of the workpiece.