Grinding method of wafer

A grinding method of a wafer having a circular disc shape by grinding a region on an inside relative to an outer circumferential edge of the wafer in a radial direction of the wafer to form a thin plate part and a ring-shaped reinforcing part that surrounds an outer circumferential part of the thin plate part in the wafer, the grinding method comprising:

• a holding step of holding the wafer by a chuck table rotatable around a rotating shaft disposed to pass through a center of the chuck table in a radial direction;
• a first grinding step of forming the ring-shaped reinforcing part by lowering a grinding wheel relative to the chuck table to bring the grinding wheel close to the wafer and grinding the wafer by bottom surfaces of a plurality of grinding abrasive stones after the holding step, the grinding wheel including a circular annular base and the plurality of grinding abrasive stones disposed along a circumferential direction of the base on one surface side of the base, an outer diameter defined by the plurality of grinding abrasive stones in a case in which the grinding wheel is rotated around a spindle disposed at a central part of the base in a radial direction being smaller than an outer diameter of the wafer;
• a second grinding step of grinding an inner circumferential side surface of the ring-shaped reinforcing part by outer circumferential side surfaces of the plurality of grinding abrasive stones by moving the grinding wheel relative to the wafer toward an outside of the wafer in the radial direction after the holding step;
• a first separation step of separating the outer circumferential side surfaces of the plurality of grinding abrasive stones from the inner circumferential side surface of the ring-shaped reinforcing part by moving the grinding wheel relative to the wafer toward the inside of the wafer in the radial direction after the first grinding step and the second grinding step;
• and
• a second separation step of separating the bottom surfaces of the plurality of grinding abrasive stones from a top surface of the thin plate part by raising the grinding wheel relative to the chuck table after the first grinding step and the second grinding step.