Control of sonoluminescence signal in deionized water using carbon dioxide

Megasonic cleaning is routinely employed in semiconductor industry for cleaning of wafers. However, the method also results in damage to wafer features and such damage has been proposed to arise from transient, imploding cavities formed during megasonic processing. Transient cavitation is associated with the release of light, a phenomenon called sonoluminescence (SL) and the extent of damage has been shown to correlate with the intensity of SL. Control of sonoluminescence may therefore allow control of damage during megasonic processing of wafers. In this study, the ability of carbon dioxide to quench sonoluminescence generation in deionized water exposed to megasonic field of varying power density and duty cycle has been systematically investigated. It has been found that CO2 is not only incapable but also a potent inhibitor of sonoluminescence, providing a potential means for selective alleviation of the violent effects of transient cavitation in process fluids. A novel chemical method has been established for in situ release of CO2 from NH4HCO3 through a pH induced shift in the carbonic acid equilibria in deionized water. Using this method, a precisely controlled, progressive decrease in SL of air saturated deionized water through addition of NH4HCO3 has been demonstrated. It has been determined that 130 ppm of released CO2 is sufficient for complete inhibition of sonoluminescence generated in air saturated deionized water.