HF- and NH4OH-treated (111)Si surfaces studied by spectroscopic ellipsometry

Spectroscopic ellipsometry has been used to study HF- and NH4OH-treated (111)Si surfaces. The ellipsometric data indicate that aqueous HF etching results in the removal of the surface oxide and leaves behind Si surfaces terminated by atomic hydrogen. Chemical treatment by aqueous NH4OH solution provides a bare Si surface, but further etching of Si leads to roughening of the sample surfaces. Both the HF- and NH4OH-treated surfaces become hydrophobic as the surface is hydrogen-terminated (HF) or the surface oxide layer is etched completely away (NH4OH).