megasonic cleaning

Megasonic cleaning uses high-frequency sound waves (0.7-1.5 MHz) in DI water to remove sub-micron particles from wafer surfaces. **Principle**: Sound waves create pressure oscillations in fluid. Acoustic streaming provides gentle scrubbing action that dislodges particles. **Frequency significance**: Megasonic (MHz) is gentler than ultrasonic (kHz). Avoids cavitation damage that ultrasonics can cause to delicate features. **Mechanism**: Acoustic streaming and boundary layer effects remove particles without mechanical contact or damaging cavitation. **Applications**: Post-CMP clean, pre-diffusion clean, photomask cleaning, critical cleans where particles cause defects. **Integration**: Built into wet benches, spray tools, or tank immersion systems. **Transducer**: Piezoelectric transducers mounted on tank bottom or immersed in fluid. **Power and frequency**: Tunable parameters to optimize cleaning for specific contamination and wafer features. **Compatibility**: Must be compatible with increasingly delicate device structures at advanced nodes. Process optimization required. **Effectiveness**: Can remove particles down to tens of nanometers. Combined with chemical cleaning for best results.