DEPTH DETECTING METHOD, ETCHING METHOD, DEPTH DETECTING DEVICE, AND ETCHING DEVICE

PROBLEM TO BE SOLVED: To accurately detect the depth of a recessed portion formed so as to open on a plane surface of an object to be measured.SOLUTION: In an etching device 10, a wafer 12 is placed and loaded on a plane electrode 24. A detecting device 50 makes a light beam LB emitted from a light source portion 52 of the wafer incident from an incident surface 12B of the wafer to the inside of the wafer. An imaging portion 54 is irradiated with a light beam LBr reflected on a reflection surface 12A on which an opening of a recessed portion is formed and emitted from an emission surface 12C, thereby imaging the light beam. A detecting device detects the depth of the recessed portion formed on the wafer by calculating the length of a shadow of the recessed portion included in the imaged light beam.