Wafer processing method and adhesive tape used in the wafer processing method

A method of processing a wafer having a plurality of streets formed on the front surface in a lattice pattern, a device area where a plurality of devices are formed in a plurality of areas sectioned by the plurality of streets, and an excess area surrounding the device area, comprising:

• a reinforcement forming step for removing an area corresponding to the device area of the rear surface of the wafer to reduce the thickness of the device area to a predetermined value and for keeping an area corresponding to the excess area of the rear surface of the wafer to form an annular reinforcement that is part of the wafer;
• an adhesive tape mounting step for mounting the front surface of an outer peripheral portion of an adhesive tape onto an opening of an annular frame to cover it, the adhesive tape having an adhesive layer and a plurality of via-holes formed in the adhesive layer;
• a frame-fixing step for placing the rear surface of a wafer affixing area of the adhesive tape mounted on the annular frame on a chuck table for suction-holding a workpiece of a processing machine and fixing the annular frame by clamps provided on the chuck table;
• a wafer affixing step for placing the rear surface corresponding to the device area of the wafer on the front surface of the wafer affixing area of the adhesive tape placed on the chuck table, suction-holding the adhesive tape onto a suction-holding area of the chuck table by exerting suction-force to the suction-holding area, and at the same time sucking the wafer through the via-holes by exerting suction-force of the suction-holding area through the via-holes to affix the wafer to the front surface of the adhesive tape;
• an excess area removing step for cutting and removing the excess area of the wafer affixed to the front surface of the adhesive tape suction-held on the suction-holding area of the chuck table by the processing means of the processing machine;
• and
• a dividing step for cutting the wafer, which has been affixed to the front surface of the adhesive tape suction-held on the suction-holding area of the chuck table and is devoid of the excess area, along the streets by the processing means of the processing machine.