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.