Characterization of Mass Transfer Rates and Contamination Kinetics on Silicon Wafer Surface

Production yield in semiconductor wafer fabrication is directly affected by low levels of molecular contamination of the silicon wafer surface. Wafers are often carried in specialized plastic enclosures, called front opening unified pods, that are continuously purged with a nitrogen flow to minimize wafer surface contamination. To improve this purge process, it is necessary to better understand the effect of mass transfer transport and kinetic processes on the silicon wafer surfaces. The experimental surface kinetics data available in the literature for diethyl phthalate were utilized, along with a validated computational fluid dynamics model to predict the relative magnitude of the time scales associated with transport and kinetics. The transport time was found to be considerably shorter than the characteristic adsorption time, and the desorption characteristic time was longer than the adsorption time. In general, surface kinetics parameters are not always known. Among other techniques, optimization techniques can be employed to calibrate the kinetic rate parameters. A multi-hierarchical model optimization technique can then be used to infer surface kinetics rates using experimentally measured concentration data for amine contamination of a wafer surface.