Damage-free Design of Megasonic Waveguide for Single Wafer Process

Abstract

Megasonic cleaning process is routinely used in the semiconductor industry for removal of contaminant particles from wafer surfaces. Effective cleaning is achieved through proper choice of chemical solutions, transducer power density and frequency of the acoustic field. Two principal mechanisms, namely acoustic streaming and acoustic cavitation, are considered to be responsible for the removal of particles from a contaminated surface. In this study, we designed two megasonic waveguides, indirect type and direct type, for a comparative study of cleaning wafers with 70 nm poly-Si pattern. We observed that the indirect type waveguide has more uniform megasonic energy which is transferred to the wafer. Also bubble size was smaller than conventional direct type. The conventional direct type waveguide is better in energy transfer, but can cause structural damages on the wafer.