Evolution of atomic-scale roughening on Si(001)-(2×1) surfaces resulting from high temperature oxidation

Abstract

Scanning tunneling microscopy was used to study surface morphology on Si(001)-(2×1) samples following elevated temperature O2 exposure as a function of pressure (1×10−8<Pox<5×10−6 Torr), temperature (500<Ts<700 °C), and dose [10–800 langmuir (L)]. At low O2 doses (Dox<50 L; Ts≥600 °C and Pox<1×10−7 Torr) preferred B-type step retraction is observed, but single A-domain formation is prevented due to step pinning by nucleated oxide clusters. These pinning centers roughen the surface via step ‘‘fingering’’ at low doses, while at higher doses result in the formation of three-dimensional conical islands, similar to oxidation-induced ‘‘growth features’’ reported previously by Smith and Ghidini [J. Electrochem. Soc. 129, 1300 (1982)] at higher temperatures. Surface etching rates were determined by measuring the island heights as a function of exposure, and a sticking coefficient s of 0.04 (±0.02) was estimated for O2 reaction on Si(001) at 600 °C. For moderate O2 doses (<1000 L) surface etching was found to dominate SiO2 growth up to pressures several orders of magnitude above the commonly accepted oxidation ‘‘critical line,’’ causing significant atomic-scale roughening under these oxidation conditions.