Synchronous Schlieren Image Analysis of Megasonic Single Wafer Cleaning

摘要

A synchronous Schlieren system for quantitative analysis of the ultrasonic field in megasonic wafer cleaning is described. We found that LSI patterns on the side of a silicon wafer opposite to the incidence of ultrasound were damaged during single-wafer cleaning. Defects were observed when ultrasound penetrated through the wafer at a certain angle of incidence. A Schlieren system with pulsed illumination synchronized to the ultrasonic phase was constructed, and the wave fronts in water around the wafer during megasonic cleaning were imaged. We found that ultrasound passed through the wafer when Lamb waves were generated in the wafer. This was confirmed with a computer simulation of the wave propagation.