Height detecting apparatus

A height detecting apparatus comprising:

• for a chuck table holding a workpiece;
• a height detector for detecting a height of said workpiece held on said chuck table;
• and
• a mover for relatively moving said chuck table and said height detect;
• said height detector including
• a light source having a predetermined wavelength band,
• a first single-mode fiber for transmitting light emitted from said light source,
• a fiber coupler connected to said first single-mode fiber,
• a Fabry-Perot tunable filter connected to said first single-mode fiber between said light source and said fiber coupler for sequentially sweeping light having a single wavelength from said wavelength band at predetermined cycles and then transmitting the light having the single wavelength,
• a chromatic aberration lens for focusing the light transmitted from said Fabry-Perot tunable filter and applying the light to said workpiece held on said chuck table,
• a return light reflected from said workpiece passing through said chromatic aberration lens, the return light being branched by said fiber coupler, the return light passing through a second single-mode fiber;
• a photodetector for detecting the return light emerging from said second single-mode fiber and outputting a signal corresponding to an intensity of the return light detected above, and
• controller having a memory for storing a table setting the relation between wavelength and height;
• said controller determining the wavelength corresponding to a highest light intensity from the wavelengths detected by said photodetector in synchronism with the predetermined cycles of sweeping of the light having the single wavelength by said Fabry-Perot tunable filter, and then checking said determined wavelength against the wavelength and height set in said table, thereby determining the height of said workpiece held on said chuck table.