Abstract: A wafer processing method includes the following steps: forming, on a back side of a wafer including a device layer, a mask to be used in forming grooves in a substrate along streets from the back side of the wafer; applying plasma etching from the back side of the wafer through the mask to form the grooves in the substrate along the streets and to define chip regions surrounded by the grooves; immersing the wafer in water, to which ultrasonic vibrations are being applied, after the etching step, whereby the device layer is cracked or ruptured along outer peripheral edges of the chip regions; and bonding a tape to a front side of the wafer before performance of the water immersion step.