Wafer processing method

A wafer processing method of processing a wafer having a device region and a peripheral surplus region formed on a top surface of the wafer, the device region having a plurality of devices demarcated by a plurality of planned dividing lines, the peripheral surplus region surrounding the device region, the method comprising:

• a modified layer forming step of forming, in a ring shape, a modified layer not reaching a finished thickness of the wafer by irradiating the wafer with a laser beam of a wavelength transmissible through the wafer from an undersurface of the wafer such that a condensing point of the laser beam is positioned in an inner part of the wafer, the inner part corresponding to the peripheral surplus region;
• a protective member disposing step of disposing a protective member on the top surface of the wafer before or after the modified layer forming step;
• a reinforcing portion forming step of making a cleavage plane reach the top surface from the modified layer formed in a ring shape, removing the modified layer, thinning a region corresponding to the device region of the wafer to the finished thickness, and forming a ring-shaped reinforcing portion in a region corresponding to the peripheral surplus region of the wafer by holding the protective member side by a chuck table and grinding the undersurface of the wafer;
• and
• an undersurface processing step of performing predetermined processing on the undersurface of the wafer.