Processing method of bonded wafer

A method of processing a bonded wafer including a first wafer and a second wafer that are bonded to each other by a bonding layer interposed therebetween, the first wafer having on a face side thereof a device region where a plurality of devices are fabricated and an outer circumferential excessive region surrounding the device region and having a chamfered outermost circumferential edge, and the face side being bonded to the second wafer by the bonding layer, the method comprising:

• a modified layer forming step of applying a laser beam having a wavelength transmittable through the first wafer to the first wafer from a reverse side thereof while positioning a focused spot of the laser beam within the first wafer to form a modified layer in the first wafer and cracks developed from the modified layer and extending toward an outer circumferential portion of the first wafer along the bonding layer;
• and,
• after the modified layer forming step, a grinding step of holding the second wafer on a chuck table and grinding the reverse side of the first wafer to thin down the first wafer, wherein,
• in the modified layer forming step, a plurality of modified layers are formed in the first wafer at positions spaced in a thicknesswise direction of the first wafer radially inwardly from the outer circumferential portion of the first wafer, and a line interconnecting the modified layers forms a depression angle ranging from 30 to 80 degrees toward the outer circumferential portion of the first wafer, the modified layers being joined to each other by cracks to form a removal initiating point for removing the chamfered outermost circumferential edge.