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 of the first wafer 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, the focused spot of the laser beam includes multi-focused spots, and a line interconnecting the multi-focused spots forms a depression angle ranging from 15 to 50 degrees toward the outer circumferential portion of the first wafer with respect to a line parallel to a plane of the bonded wafer, the cracks being formed from the modified layer formed by the multi-focused spots toward the bonding layer and developed along the bonding layer to form a removal initiating point for removing the chamfered outermost circumferential edge.