Patent ID: 7776721

Claim:
A laser processing method for a gallium arsenide wafer in which a laser beam is radiated along streets of said gallium arsenide wafer in which devices are formed in a plurality of regions obtained through partition by said streets formed in lattice on a surface of said gallium arsenide wafer, thereby cutting off said gallium arsenide wafer along said streets, said method comprising: a wafer supporting step for sticking a rear surface of said gallium arsenide wafer on a protective member; a shielding film coating step for coating an upper surface of said gallium arsenide wafer having said rear surface stuck on said protective member with a debris shielding film; a laser-processed trench forming step for radiating a laser beam with a wavelength having an absorption property for said gallium arsenide wafer along said streets from said debris shielding film side to said gallium arsenide wafer having said surface coated with said debris shielding film, thereby forming laser-processed trenches each not reaching said rear surface along said streets; and a cutting-off step for radiating the laser beam with the wavelength having the absorption property for said gallium arsenide wafer along said laser-processed trenches to said gallium arsenide wafer having said laser-processed trenches formed therein, thereby forming cut-off trenches each reaching said rear surface along said respective laser-processed trenches to thereby divide said wafer into individual devices and simultaneously having debris generated by the radiation of the laser beam attach to wall surfaces of said cut-off trenches, and wherein said debris attached to the wall surfaces of said cut-off trenches are not removed from the devices but allowed to remain attached to the devices and thereby increase the transverse rupture strength of said devices.