Wafer processing method
A wafer processing method includes bonding one surface of a first wafer to a second wafer, the first wafer having a device region on the one surface, a peripheral surplus region, and a chamfered peripheral edge; forming an annular modified layer along a boundary of the device region and the peripheral surplus region by applying a laser beam to the first wafer from the other surface of the first wafer with a focal point of the laser beam placed at the boundary; after forming the modified layer, grinding the first wafer from the other surface to thin the first wafer to a finished thickness; and exerting an external force on the peripheral surplus region that is close to the peripheral edge with respect to a region in which the modified layer is formed, to thereby facilitate the separation of the peripheral surplus region.
1 . A wafer processing method comprising:
a bonded wafer forming step of forming a bonded wafer by bonding one surface of a first wafer to one surface of a second wafer, the first wafer having a device region in which a plurality of devices are formed on the one surface, a peripheral surplus region surrounding the device region, and a chamfered peripheral edge;
a modified layer forming step of forming an annular modified layer along a boundary of the device region and the peripheral surplus region of the first wafer by applying a laser beam having such a wavelength as to be transmitted through the first wafer to the one surface of the first wafer from another surface of the first wafer that is opposite to the one surface thereof, with a focal point of the laser beam placed at the boundary;
a grinding step of, after the modified layer forming step, grinding the first wafer of the bonded wafer from the other surface of the first wafer to thin the first wafer to a finished thickness; and
an external force exerting step of, during or after the grinding step, exerting an external force on the peripheral surplus region that is close to the peripheral edge with respect to a region in which the modified layer is formed in the modified layer forming step, to thereby facilitate separation of the peripheral surplus region.
2 . The wafer processing method according to claim 1 , wherein, in the modified layer forming step,
the laser beam is applied to the first wafer in such a manner that the focal point of the laser beam is sequentially placed at a position closer to the one surface of the first wafer toward the peripheral edge, to thereby form the modified layer in a shape extending along a side surface of a truncated cone inclined from the one surface toward the other surface of the first wafer.
3 . The wafer processing method according to claim 1 , wherein, in the modified layer forming step,
the laser beam is applied to the first wafer in such a manner that cracks extending from the modified layer do not appear on the one surface side of the first wafer, to thereby restrain the peripheral surplus region from being separated from the first wafer while the grinding step is carried out, but separate the peripheral surplus region from the first wafer in the external force exerting step.
4 . The wafer processing method according to claim 1 , wherein, in the external force exerting step,
an ultrasonic wave is applied to the peripheral surplus region to thereby facilitate the separation of the peripheral surplus region.
5 . The wafer processing method according to claim 1 , wherein, in the external force exerting step,
at least one of fluid or a solid is blown to the peripheral surplus region to thereby facilitate the separation of the peripheral surplus region.
6 . The wafer processing method according to claim 1 , wherein, in the external force exerting step,
a pressing member capable of moving in a direction perpendicular to the one surface of the first wafer exerts a load on the peripheral surplus region to thereby facilitate the separation of the peripheral surplus region.