Dissolution kinetics for atomic, molecular, and ionic contamination from silicon wafers during aqueous processing

Experimental measurements have been made by total reflection X-ray fluoresc ence spectroscopy of dissolution of Ii and Cl from p-type silicon wafers by deionized water. The dissolution rate of these ions is initially rapid, th en slows dramatically and the surface coverage appears to reach equilibrium at approximately 6 x 10(12) and 2 x 10(12) atom/cm(2) for K and Cl, respec tively. These results and others have been fit to a general model for conta minant removal during aqueous processing of silicon wafers. For a two-dimen sional wafer cleaning geometry, the convective diffusion equation is solved , including the effects of first-order contaminant deposition and dissoluti on, which enter as a surface boundary flux condition. Results are presented of simulations fur diffusion only, for convection of continuously renewed process solution, and for convection of recirculated, contaminated process solution, The results demonstrate the importance of convection in transport ing contaminants away from the wafer surface, thus preventing redeposition. These calculations predict that contaminant removal can vary by an order o f magnitude across the wafer surface due to high solution-phase contaminant concentrations in the downstream direction. These results are supported by recent studies which report a dependence of contaminant dissolution rate o n the cleanliness of the bulk process solution. (C) 1999 The Electrochemica l Society. S0013-4651 (99)02-050-9. All rights reserved.