Aqueous Etching Produces Si(100) Surfaces of Near-Atomic Flatness: Strain Minimization Does Not Predict Surface Morphology

Abstract

A simple, room temperature process—etching of Si(100) surfaces in 40% NH4F(aq) solutions—produces H-terminated surfaces of near-atomic smoothness over large areas (>1000 × 1000 Å2). The etched surface is primarily terminated by long alternating rows of strained and unstrained silicon dihydrides; no microfaceting or etching-induced surface roughness is observed. The Cartesian components of the infrared absorption spectrum of flat and vicinal etched surfaces show that the surface is almost entirely dihydride-terminated. This analysis disproves previous assignments of the infrared spectrum of NH4F-etched Si(100) which suggested that the etched surface was very rough and terminated by a variety of mono-, di-, and trihydride species. Although the steady-state etch morphology has lower interadsorbate strain than bulk-terminated H/Si(100), this morphology does not minimize interadsorbate strain as previously postulated. The relatively low reactivity of the strained dihydrides kinetically blocks this pathway.