Chemical treatment effect of Si(111) surfaces in F-based aqueous solutions

Chemically treated Si(111) surfaces in aqueous HF (1.5%), NH4F (40%), and HBF4 (42%) solutions at 20 °C have been studied using spectroellipsometry (SE), ex situ atomic force microscopy (AFM), and contact-angle measurement techniques. The SE data clearly indicate that the solutions cause the removal of the native SiO2 film with etch rates of ∼72 (HF), ∼13 (NH4F), and ∼8 Å/min (HBF4), respectively. The SE data also indicate that when the native oxide film is completely etch removed, the resulting surface is slightly roughened. The roughened surface thicknesses are estimated to be ∼3 Å, in reasonable agreement with the AFM rms values. The measured contact angles suggest that the HF- and NH4F-treated surfaces are hydrophobic, while the HBF4-treated surface is, if anything, hydrophilic.