Influence of gasification on the performance of a 1 MHz nozzle system in megasonic cleaning

Single-wafer cleaning based on megasonic nozzle systems can be used for removing nano-particles. An optimized cleaning process must deliver a high degree of cleaning uniformity with a minimal amount of structural damage. However, the cleaning liquid is confined to a sonicated liquid jet, which is ejected by the nozzle. As a result, a high degree of complexity is introduced to the cleaning process due to the strong interdependencies between acoustic, electric and hydrodynamic characteristics of such systems. In the present work, the influence of the gas content of the cleaning liquid on the performance of a 1 MHz nozzle system is investigated and related to the intrinsic properties of the water jet. Cleaning tests are performed and the cleaning results are correlated to the electrical responses of the driving transducer. The electrical response depends both on the gasification of the liquid and the occurrence of acoustic reflections. Furthermore, Schlieren- and Sonoluminescence-imaging of the cleaning system are performed. The imaging techniques can identify the impact of bubbles on the propagation of acoustic waves and the resonant excitation of cleaning cavitation throughout the liquid column