Characterization of Si(111) surfaces treated in aqueous H2SiF6 solution

Chemically treated Si(111) surfaces in aqueous (40%) H2SiF6 solution have been investigated using spectroscopic ellipsometry (SE), ex situ atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact-angle measurements. For comparison, Si(111) surfaces etched in 1.5% HF solution have been examined. The measured SE data clearly indicate an evidence for the removal of surface native oxide by these solutions. When the native oxide is completely etch-removed, the resulting surface is slightly roughened. The roughened overlayer thicknesses estimated from SE are ∼0.3 nm, in reasonable agreement with the AFM observation (rms values of ∼0.2 nm). The XPS data suggest considerable amounts of fluorine species on the H2SiF6-treated surface. The HF-etched surface is found to be hydrophobic, while the H2SiF6-treated one is, if anything, hydrophilic. The Si–O–F groups detected on the H2SiF6-treated surface may be one of the causes for the hydrophilicity.