Crack and thickness detecting apparatus

A crack and thickness detecting apparatus for detecting a crack in a wafer held on a rotating chuck table and also detecting the thickness of said wafer, said crack and thickness detecting apparatus comprising:

• an ultrasonic oscillating unit oscillating a first ultrasonic wave toward the upper surface of said wafer held on the chuck table at a predetermined incident angle;
• an ultrasonic oscillating and receiving unit oscillating a second ultrasonic wave toward the upper surface of said wafer in a direction perpendicular thereto and also receiving said first ultrasonic wave and said second ultrasonic wave propagated and reflected in said wafer;
• a pulse voltage generating unit applying a pulse voltage to said ultrasonic oscillating unit and said ultrasonic oscillating and receiving unit;
• a crack determining unit determining whether or not the crack is present in said wafer from waveform information on said first ultrasonic wave received by said ultrasonic oscillating and receiving unit;
• and
• a thickness calculating unit calculating the thickness of said wafer from waveform information on said second ultrasonic wave received by said ultrasonic oscillating and receiving unit,
• wherein said ultrasonic oscillating unit and said ultrasonic oscillating and receiving unit alternately oscillate said first ultrasonic wave and said second ultrasonic wave to said wafer held on said rotating chuck table with a time difference, and said ultrasonic oscillating and receiving unit alternately receives said first ultrasonic wave and said second ultrasonic wave,
• said first ultrasonic wave oscillated by said ultrasonic oscillating unit and applied obliquely to said wafer is propagated in said wafer and irregularly reflected by the crack in said wafer, and said crack determining unit determines the presence of the crack in said wafer in the case that said ultrasonic oscillating and receiving unit receives a reflected wave obtained by the irregular reflection of said first ultrasonic wave, and
• said second ultrasonic wave oscillated by said ultrasonic oscillating and receiving unit and applied perpendicularly to said wafer is reflected on the upper surface of said wafer to generate an upper surface reflected wave, propagated in said wafer and also reflected on the lower surface of said wafer to generate a lower surface reflected wave, and said thickness calculating unit calculates the thickness of said wafer from a time difference between the reception of said upper surface reflected wave and the reception of said lower surface reflected wave by said ultrasonic oscillating and receiving unit.