Effect of Dissolved CO2 in De-Ionized Water in Reducing Wafer Damage During Megasonic Cleaning in MegPie

Abstract

Particle removal from wafer surfaces can be accomplished by irradiation of cleaning fluid by sound waves in the MHz frequency range. Unfortunately, unless proper cleaning conditions are chosen, megasonic irradiation may also result in damage to fragile wafer features. Here, we demonstrate a strong effect of dissolved CO2 levels on the reduction of wafer damage during megasonic cleaning. Test structures with L/S patterns were irradiated with 0.93 MHz sound waves at varying power densities and dissolved CO2 levels, in a single wafer spin cleaning tool, MegPie®. Dissolution of increasing amounts of CO2 in air saturated DI water caused a significant decrease in the number of breakages to line structures and also decreased the lengths of the line breakages, at all power densities up to 2.94 W/cm2. This ability of dissolved CO2 to protect against feature damage correlates well with its ability to suppress sonoluminescence in sound irradiated DI water.