HF/Alcohol Preparation of Wafers for the Reduction of Haze in Low Temperature Si Epitaxy by Remote Plasma Chemical Vapor Deposition

Abstract

The use of an aqueous HF dip as the final ex situ cleaning step following a modified RCA clean before growth of epitaxial Si layers by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been found to cause haze. Two approaches have been employed to eliminate the haze: addition of alcohol to lower the surface energy of the HF solution, and the application of the HF solution by a spin etch technique. We have studied final ex situ treatments with water/HF, ethanol/HF and methanol/HF solutions applied by both dip and by spin methods, and their effects on haze in low temperature Si homoepitaxy by RPCVD. The ratios of solvent to 49% HF (aq) were 40:1, 10:1 and 5:1. Surface carbon and oxygen levels, as measured by Auger Electron Spectroscopy (AES) after the HF solution treatments were found to be comparable for the alcohol/HF and water/HF dips. For the spin application, methanol/HF resulted in higher surface carbon coverage than for ethanol or water HF solutions. Epitaxial silicon films, 2000–4000Å thick, were grown on the wafers at 450°C using RPCVD. Secondary Ion Mass Spectroscopy (SIMS) measurements showed elevated levels of oxygen and carbon contamination at the epi-substrate interface to result when the wafers were treated with water/HF solutions rather than alcohol/HF, but no advantage was observed for the spin versus the dip technique. Films which were cleaned by water/HF exhibited patterns of haze over the wafer surface showing flow lines where the liquid drained from the surface for both dip and spin applications. The alcohol/HF solutions resulted in substantial reduction in haze for the dip application and elimination of haze for the spin application.