Impact of Re-Gasified Water on Megasonic Cleaning

Abstract

Megasonic cleaning using de-gassed water (less than 2ppm N2, O2, CO2) in a 300mm batch immersion tool often does not give optimal particle performance, with particle streaks and clusters added onto the wafer, and low particle removal efficiency (PRE). When water was re-gasified with N2, the resultant stable cavitation activity reduced particle adders and increased PRE. With N2 concentration increased to just above 5ppm, number of particle adders decreased by three folds. Optimal particle performance could be obtained by operating at an N2 level close to saturation.