Ultrasonic cleaning machine is a kind of cleaning equipment widely used in the microelectronics industry. The principle of ultrasonic cleaning is that under the strong ultrasonic effect (the commonly used ultrasonic frequency is 20-40khz), the inside of the cleaning agent will produce sparse and dense parts, and the sparse part will produce nearly vacuum cavity. When the cavity disappears, strong local pressure will be generated nearby, it breaks the chemical bond in the molecule and desorbs the impurities on the surface of the sapphire wafer. When the ultrasonic frequency and the vibration frequency of the cavity resonate, the mechanical force reaches the maximum, and a large amount of heat energy accumulates in the bubble, which makes the temperature rise and promotes the occurrence of the chemical reaction. The improvement of ultrasonic power is helpful to promote the cleaning effect. Because the removal effect of the ultrasonic cleaning machine for small particles less than 1 μm is not ideal, the ultrasonic cleaning machine is mostly used to remove large contaminated particles attached to the surface of the sapphire wafer.
Megasonic cleaning machine not only preserves the advantages of the ultrasonic cleaning machine but also overcomes the shortcomings of the ultrasonic cleaning machine. The mechanism of megasonic cleaning is to clean the sapphire wafer through a high-frequency vibration effect. During cleaning, the transducer emits high-energy sound waves with a wavelength of 1.5 μm and a frequency of 0.8 MHz. Under the push of this sound wave, the solution molecules move at high speed and its maximum instantaneous speed can reach 300 mm/s. Therefore, it is impossible to form cavities like ultrasonic clexaning, the only high-speed fluid wave can continuously impact the wafer surface, so that the dirt and fine particles attached to the sapphire chip surface are forced to be removed and enter the cleaning solution. The particles less than 0.2 μm on the wafer surface can be removed by megasonic cleaning, which has no effect on the ultrasonic waves. At present, megasonic cleaning machine has become an effective equipment for sapphire wafer cleaning.