Morphology of hydrofluoric acid and ammonium fluoride-treated silicon surfaces studied by surface infrared spectroscopy

Morphologies of Si surfaces treated with aqueous solutions of hydrofluoric acid (HF) and ammonium fluoride (NH₄F) have been investigated using surface infrared spectroscopy. We confirm that HF-treated Si(111) surfaces are terminated with a monohydride (Si - H), dihydride (Si - H₂), and trihydride (Si-H₃), whereas NH₄F-treated Si(111) surfaces are dominantly terminated with Si - H. For Si(100), treatment in NH₄F produces a surface for which the dihydride mode is enhanced compared to HF treatment, suggesting that surface Si - Si bonds on Si(100) are readily cleaved in a NH₄F solution to generate a dihydride Si. The effect of varying the HF concentration on the morphology of HF-treated Si(100) surfaces is investigated. It is demonstrated that 5% HF treatment produces Si(100) surfaces which have a larger density of surface Si - Si bonds than 50% HF or 0.5% HF treatment.