Megasound cleaning technology principle

Introduction

As semiconductor manufacturing processes move toward smaller linewidths, the cleanliness requirements for wafer surfaces become increasingly stringent, especially for the removal of submicron particles. Megahertz ultrasonic cleaning technology, with its unique advantages in efficiently removing tiny particles, has become an effective method for cleaning polished wafers.

I. Overview of Megahertz Ultrasonic Cleaning Technology

Megahertz ultrasonic cleaning technology uses the energy of high-frequency sound waves (typically 0.8-1.0 MHz) in combination with chemical cleaning agents to clean silicon wafers. Its core lies in the synergistic effect of physical action produced by high-energy frequency vibration and chemical reagents to remove particles smaller than 0.2μm from the wafer surface. This achieves a cleaning effect that is difficult to achieve with traditional ultrasonic cleaning, while also combining the functions of mechanical scrubbing and chemical cleaning.

II. Principle of Megahertz Ultrasonic Cleaning

The principle of megahertz ultrasonic cleaning is mainly based on the following physical effects:

Acoustic pressure gradient effect: High-frequency sound waves propagating in the cleaning solution produce a significant acoustic pressure gradient.

Particle velocity effect: Cleaning solution molecules move at high speed under the impetus of sound waves, with a maximum instantaneous velocity of up to 30 cm/s.

Acoustic streaming effect: Sound wave energy causes the cleaning solution to produce overall flow (acoustic streaming).

Minor cavitation effect: Due to the extremely high frequency (megahertz level), sound waves in the cleaning solution are difficult to produce effective cavitation bubbles (i.e., the main cavitation effect in ultrasonic cleaning). The cleaning process does not form a large number of bubbles; it mainly relies on the high-speed micro-water flow formed in the cleaning solution by high-frequency sound wave energy.

III. Particle Removal Process

The transducer emits high-energy sound waves with a wavelength of approximately 1μm and a frequency of 0.8 MHz, which are transmitted to the cleaning solution via a megahertz ultrasonic plate. The high-speed movement of the cleaning solution molecules forms micro-water streams that continuously impact the wafer surface. The directional impact force of this high-speed micro-water stream (strong cleaning directionality, usually requiring the part surface to be placed parallel to the sound beam) can forcibly detach submicron (<0.2μm) contaminants and small particles adhering to the surface and carry them away into the cleaning solution.

IV. Factors Affecting Particle Removal Rate

The particle removal effect of megahertz ultrasonic cleaning is closely related to the following factors:

Cavitation effect of acoustic streaming (although weak, it still exists)

Solubility of gases in the cleaning solution

Oscillation effect produced by sound waves

Use of chemical cleaning agents (especially surfactants): Surfactants can effectively prevent the removed particles from redepositing on the wafer surface and are an important means of achieving efficient cleaning.

Conclusion

Megahertz ultrasonic cleaning technology, with its unique high-frequency physical mechanism (acoustic pressure gradient, particle velocity, acoustic streaming) combined with chemical action, has become an effective means of removing submicron particles from the surface of polished silicon wafers. It overcomes the limitations of traditional ultrasonic cleaning in removing tiny particles and has advantages such as high cleaning precision and strong directionality. It has important application value in fields with high cleanliness requirements such as semiconductor manufacturing.

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