Patent ID: 8847108

Claim:
A laser beam machining apparatus comprising: a chuck table having a workpiece holding surface for holding a workpiece to be machined; machining laser beam oscillating means for oscillating a machining pulsed laser beam for machining said workpiece held on said chuck table; a condenser for condensing said machining pulsed laser beam oscillated by said machining laser beam oscillating means, wherein said condenser includes a condenser lens and an actuator for moving said condenser lens in a direction perpendicular to the workpiece holding surface; condensing point position adjusting means for displacing a condensing point position of said machining pulsed laser beam condensed by said condenser; height position detecting means for detecting the height position of an upper surface of said workpiece held on said chuck table, said height position detecting means including detection laser beam oscillating means for oscillating a laser beam different in wavelength from said machining pulsed laser beam, a detection laser beam irradiation path for guiding said detection laser beam oscillated by said detection laser beam oscillating means to said condenser, a detection laser beam reflection path for guiding a reflected beam generated upon reflection by said workpiece held on said chuck table of a laser beam radiated through said detection laser beam irradiation path and said condenser, reflected beam analyzing means which is disposed in said detection laser beam reflection path so as to analyze said reflected beam reflected on said upper surface of said workpiece, and condensing point position displacing means for displacing the condensing point position of said detection laser beam and the condensing point position of said machining pulsed laser beam; control means for controlling said actuator of said condenser and said condensing point position adjusting means on the basis of a detection signal from said height position detecting means; and feeding means for continually feeding said workpiece relative to said condenser while irradiating both the detection laser beam and the machining pulsed laser beam simultaneously onto said workpiece thereby forming a denatured layer at an even, predetermined position of depth from the upper surface of said workpiece by allowing movement of said condenser up and down corresponding to a ruggedness of said workpiece to thereby keep a distance from said condenser to the upper surface of said workpiece constant.