Wafer processing method

A wafer processing method including a substrate and a device layer stacked over a surface of the substrate, the wafer having devices formed in respective regions divided by a plurality of intersecting streets, the method comprising:

• a mask forming step of forming, on a back side of the wafer, a mask to be used in forming a plurality of etched grooves in the substrate along the streets from the back side of the wafer;
• a plasma etching step of applying plasma etching from the back side of the wafer through the mask after performing the mask forming step, thereby forming the etched grooves in the substrate along the streets and defining chip regions surrounded by the etched grooves;
• a water immersion step of immersing the wafer in water, to which ultrasonic vibrations are being applied by an ultrasonic vibrator, after performing the plasma etching step, thereby forming cracks in the device layer along outer peripheral edges of the chip regions or rupturing the device layer along the outer peripheral edges of the chip regions;
• and
• a tape bonding step of bonding a tape to a front side of the wafer before performing at least the water immersion step,
• wherein the devices are separated from the tape after performing the water immersion step.