Application of novel ultrasonic cleaning equipment that uses the waveguide mode for the single-wafer cleaning process

We demonstrate single-wafer cleaning using waveguide-type ultrasonic equipment. The waveguide vibrates as a Lamb wave, and ultrasonic waves of 900 kHz, which is within the megasonic frequency range, radiate from the waveguide side. The waveguide creates a traveling wave field between the waveguide side and wafer surface owing to ultrasonic absorption into the water at the waveguide end. For a traveling wave field, the obtained particle removal efficiency (PRE) was as good as that obtained with conventional batch-type equipment, and cavitation bubble collapse, which induces pattern defects on semiconductor devices, was suppressed. Cavitation bubble collapse was observed using wafers coated with photoresist film, and images of sonoluminescence were captured with a charge coupled device (CCD) camera system.