Studies of Si 111/ surfaces treated in aqueous fluorine-based solutions

Chemically treated Si 111. surfaces in aqueous HF, HBF4and NH4BF4 solutions have been studied using X-ray photoelectron spectroscopy XPS., spectroscopic ellipsometry SE., ex situ atomic force microscopy AFM.and contact-angle measurements. The XPS spectra clearly indicate that all these solutions etch silicon native oxide. The cleanness for the HBF4- or NH4BF4-treated surface is also found to be much worse than that for the HF-treated surface. The SE data provide an evidence that when the silicon native oxides are completely etch-removed, the resulting surfaces are slightly roughened. The roughened overlayer thicknesses estimated are ;0.3–0.4 nm which are slightly larger than the AFM values ;0.2 nm.; the difference may be due to the SE technique being sensitive to both the surface microroughness and the adsorbed chemical species. The HBF4- and NH4BF4-treated surfaces are also found to be hydrophilic, in contrast to the HF-treated one hydrophobic.. q1999 Elsevier Science B.V. All rights reserved.