Megasonic cleaning

Megasonic cleaning is a type of acoustic cleaning related to ultrasonic cleaning. It is a gentler cleaning mechanism that is less likely to cause damage. Megasonic cleaning is used in the electronics industry for various semiconductor device fabrication processes.

Like ultrasonic cleaning, megasonic cleaning uses a transducer that usually sits on top of a piezoelectric substrate. The transducer creates an acoustic field at a much higher frequency (typically 0.8–2 MHz) than ultrasonic cleaning (20-200 kHz). As a result, the cavitation that occurs is gentler and on a much smaller scale.

Comparison to ultrasonic cleaning
Megasonic cleaning differs from ultrasonic cleaning in the frequency that is used to generate the acoustic waves. Ultrasonic cleaning uses lower frequencies and it's mechanism relies on cavitation, while megasonic cleaning uses higher frequencies and produces less damaging cavitation.

In ultrasonic devices, cavitation occurs throughout the tank, and all sides of submerged parts are cleaned. In megasonic devices, the acoustic wave is found only in a line of sight from the transducer surface. For this reason, megasonic transducers are typically built using arrays of closely spaced square or rectangular piezo devices that are bonded to a substrate. Semiconductor wafers are typically cleaned in carriers holding the substrates perpendicular to the transducer, allowing both the front and back surfaces to be cleaned. Special carriers are sometimes used to reduce any obstructions that may prevent parts of the wafer surface from being cleaned.

Megasonic cleaners come in many configurations, such as single or dual nozzle systems, or single-wafer transducers. In single-wafer devices, the wafer rotates on a spinning tool and the megasonic waves are applied from above by the nozzle (liquid stream) or by the face-to-face transducer (partial area excited by megasound).