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.[1] Megasonics are currently used mainly in the electronics industry for preparation of silicon wafers.[2]
Similar to ultrasonic cleaning, megasonics utilizes a transducer that usually sits atop a piezoelectric substrate. The transducer creates an acoustic field at a much higher frequency (typically 0.8–2 MHz) compared to ultrasonic cleaning (20-200 kHz). As a result, the cavitation that occurs is gentler and on a much smaller scale.
Megasonic cleaning differs from ultrasonic cleaning in the frequency that is used to generate the acoustic waves. Ultrasonic cleaning uses lower frequencies, and produces random cavitation. Megasonic cleaning uses higher frequencies, and produces controlled cavitation. As a result, damage caused by cavitation is minimized in megasonic baths.
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 square or rectangular piezo devices bonded to a substrate, and spaced as close together as possible. Semiconductor wafers are typically cleaned in carriers holding the substrates perpendicular to the transducer so that both front and back surfaces can be cleaned. Special carriers are sometimes used to reduce any obstructions that may prevent parts of the wafer surface from being cleaned.[2]
Megasonic cleaners come in many configurations, such as single- or dual- nozzle systems, or single-wafer transducers. In these devices the single wafer is turning 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).[3]