The suitability of ultrasonic and megasonic cleaning of nanoscale patterns in ammonia hydroxide solutions for particle removal and feature damage
Chun-Lin Chu, Te-Yun Lu, Yiin‐Kuen Fuh
Abstract
Abstract In this study, usually, arrays of square or rectangular piezo devices bonded to a substrate and spaced as close together as possible for transduction for efficient megasonic cleaning, megasonic cleaning is applied to removing sidewall particles during post-silicon etch cleaning. A system was developed containing different measures of ultrasonic and megasonic processes, generated by adjusting the power in NH 4 OH. Megasonic waves in the gap between the wafer and the megasonic transducer ensure uniform sonic energy across the whole wafer. The generation of radicals is promoted by megasonic energy, such that residue removal occurs in dilute solution. The feature damage for the megasonic cleaning decreased in the NH 4 OH solution compared to ultrasonic. Moreover, the mechanical force of the bubble cavitation generated by megasonic cleaning also improves residue removal and enhances the mass transfer rate. Extreme cavitation is beneficial for removing particles but can damage wafer features. The damage caused by ultrasonic cleaning is significantly larger than megasonic cleaning. Compared with typical methods of silicon oxide residues removal, this megasonic process has a low material loss and a high residue removal efficiency for via, with a high aspect ratio. In addition, it minimizes defects to structures. These results suggest that megasonic cleaning can be applied to the nanoparticle cleaning process. Megasonic cleaning is quickly becoming an efficient method for post process cleaning in IC fabrication processes.