Method for producing wafers using ultrasound

A wafer producing method for producing a wafer from an ingot after forming a separation layer inside the ingot by setting a focal point of a laser beam having a transmission wavelength to the ingot inside the ingot at a predetermined depth from one end surface of the ingot, the predetermined depth corresponding to a thickness of the wafer to be produced, and next applying the laser beam to the ingot, the wafer producing method comprising:

• a first ultrasonic vibration applying step of applying ultrasonic vibration to a given area of the ingot at a first density to thereby form a partially broken portion where a part of the separation layer is broken;
• a second ultrasonic vibration applying step of applying the ultrasonic vibration to a whole area of the ingot larger than the given area at a second density lower than the first density, after performing the first ultrasonic vibration applying step, thereby forming a fully broken portion where the separation layer is fully broken in such a manner that breaking starts from the partially broken portion;
• and
• a separating step of separating the wafer from the ingot along the fully broken portion.