ABSTRACT
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Overview of Megasonic Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 Megasonic Cleaning Compared with Ultrasonic Cleaning . . . . . . . . . . . . . . . . . . . 235 Application of Megasonic and Ultrasonics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Discussion of Underlying Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 Properties of Piezoelectric Transducers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 Particle Attraction and Removal Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Principal Mechanisms of Megasonic Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Acoustic Cavitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Acoustic Streaming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 Significance of the Boundary Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Cleaning Chemistry and Other Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Cleaning Chemistries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 Other Cleaning Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Design Considerations for Megasonic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
INTRODUCTION
Megasonics has been a widely accepted cleaning method for contamination-sensitive products for nearly 20 years. Megasonics was initially developed in the early 1940s as a result of U.S. Navy research into advanced sonar instrumentation for antisubmarine warfare. In the late 1970s, RCA adapted this technology for wafer cleaning, and by 1982 commercial megasonic cleaning equipment was being delivered to the semiconductor industry.
