In this paper we report on studies of the mechanisms responsible for HF/H2O etching and cleaning of Si surfaces. From these studies we have clearly established that the role of water is to provide a condensed solvent medium for the HF on the surface. Our results, as well as those in the literature, show that if the partial pressures of HF and H2O are too low (or sample temperature too high), condensation does not occur and little or no etching is observed. Based on these ideas, and pressure data from the literature, we have developed a detailed model that provides for the calculation of the onset of condensation as a function of wafer temperature and reactant partial pressures. In addition, the model allows determination of the HF concentration in the condensed H2O film. Comparison of etch rates obtained for aqueous etching as a function of HF concentration, and vapor phase etching as a function of calculated HF concentration, show good agreement. The vapor phase etch rate data, as a function of wafer temperature, total HF + H2O pressure, and partial pressure ratios, will be presented in detail along with information on the model.

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