Patent ID: 8431861

Claim:
A height position detecting apparatus for detecting a height position of an upper surface of a workpiece which is transmissive to visible light and held on holding means, comprising: laser beam oscillating means for oscillating a laser beam; annular spot forming means for forming a spot shape of the laser beam oscillated by the laser beam oscillating means into an annular shape; a beam splitter for guiding into a first path the laser beam with the annular spot shape formed to be annular by the annular spot forming means; a condenser for condensing the laser beam guided into the first path so as to irradiate at least the upper surface of the workpiece held on the holding means with the condensed laser beam; a pinhole mask disposed in a second path into which the laser beam reflected on the workpiece held on the holding means is dividedly guided by the beam splitter, the pinhole mask permitting therethrough passage of the laser beam reflected on the upper surface of the workpiece and blocking the laser beam reflected on a lower surface of the workpiece; diffusing means for diffusing the laser beam, the diffusing means being disposed on the second path at a position on a downstream side relative to the pinhole mask; detection means having a detecting surface with a predetermined area for detecting the intensity of the laser beam diffused by the laser beam diffusing means, the detection means being disposed at a substantially central position of the annular spot of the laser beam; and control means for calculating the height position of the upper surface of the workpiece held on the holding means, based on the intensity of the reflected light detected by the detection means.