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Wet cleaning of silicon wafers is an essential step in the fabrication of semiconductor devices. With diminishing feature and, consequently, critical particle sizes, cleaning requirements have become even more stringent. Hence, it is imperative that an understanding of the cleaning process be obtained in order to achieve the desired cleaning efficiencies. Ultrasonic and megasonic cleaning baths are the norm in advanced fabrication lines for batch cleaning of wafers. The fluid flow in these baths is quite complex and strongly influences removal of contaminant matter from the wafer surface. To better understand the effect of fluid flow on cleaning of polymeric contaminants, chemical etch experiments have been conducted using a cleaning solution on tetra-ethyl orthosilicate (TEOS) blanket wafers. The experimental results indicate a certain degree of nonuniformity and asymmetry in an otherwise symmetric system. A qualitative analysis of the observed nonuniformity has been conducted through computational fluid dynamics (CFD) simulations of the flow within the tank using a commercial CFD tool, FLUENT 6.2. An analogous heat transfer model has been set up with the CFD model, to simulate mass transfer effects resulting from the etching of the TEOS film in the experiments. A comprehensive sensitivity analysis has also been conducted within the CFD model for various parameters that might be responsible for the experimental asymmetry.
Date of Publication: Aug. 2009