Patent attributes
A via hole depth detector for detecting the depth of a via hole formed in a workpiece held on a chuck table, comprising: a first surface position detection means which comprises a first detection laser beam oscillation means for oscillating a first detection laser beam having a predetermined wavelength and detects the height position of an illuminated portion of the workpiece based on the reflected light of the first detection laser beam; a second surface position detection means which comprises a second detection laser beam oscillation means for oscillating a second detection laser beam having a wavelength different from the wavelength of the first detection laser beam and detects the height position of an illuminated portion of the workpiece based on the reflected light of the second detection laser beam; and a control means for obtaining the depth of the via hole formed in the workpiece based on a detection value obtained by the first surface position detection means and a detection value obtained by the second surface position detection means.
