US Patent 7443517 Measuring instrument and laser beam machine for wafer

A measuring instrument for a wafer for measuring the thickness of a wafer held on a chuck table using a laser beam includes a condenser for condensing and irradiating the laser beam on the wafer held on the chuck table, a light reception unit for receiving reflected light of the laser beam irradiated upon the wafer, a convergence light point changing unit for changing the convergence light point of the laser beam, and a control unit for measuring the thickness of the wafer based on a change signal from the convergence light point changing unit and a light reception signal from the light reception unit. The control unit stores a thickness control map. The control unit controls an angle adjustment actuator, provided for adjusting the installation angle of a pair of mirrors, to change the installation angle and detects two peaks of the light amount based on the reception signal from the light reception unit.