Abstract
Acoustic methods are being increasingly used in semiconductor processing. Given the increase in circuit densities being implemented on semiconductor chips the requirements for particulate contamination tolerance are becoming more stringent. The semiconductor industries road-mapped specifications for 1998, 0.25 μm feature size require control of all particulate contaminants larger than 0.08 μm. Fine cleaning of post CMP wafers is currently being done by using the megasonics process. The cleaning effectiveness depends on the strength of the acoustic fields used. In using high-intensity, high-frequency acoustic fields it is crucial to ensure that the surface of the silicon wafer does not suffer any damage due to cavitation. This paper assesses the damage potential of semiconductor wafers to acoustic microcavitation. Acoustic microcavitation is brought about by low megahertz acoustic fields giving rise to micron size bubbles that live a few microseconds. In exposing a surface to continuous waves one could obtain cavitation effects in an average, overall sense; the details of nucleation, evolution of inertial events, however, get glossed over. Both, pulsed and cw insonification were studied. Experimental measurements of the thresholds for cavitation damage of semiconductor wafers will be presented.
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