ETCHING MECHANISM AND ATOMIC-STRUCTURE OF H-SI(111) SURFACES PREPAREDIN NH4F

The atomic structure of H-terminated Si(111) surfaces is investigated by in-situ STM and electrochemical measurements in NH4F solutions of 2 < pH < 8. Etch rate measurements show only a slight pH-dependence bet ween pH 2 and 14, when including alkaline solutions. Electrochemical r esults indicate that the etching comprises two components, one chemica l and the other electrochemical, whose relative importance depends on the pH. The possible reactants involved in the etching are studied by varying the composition of the solutions. Models describing the surfac e processes at the molecular level are;presented. The main conclusion of this work is that the nature of the chemical etching tends to smoot hen the surface, as is the case in buffered ammonium fluoride where id eally hat surface can be prepared, whereas the electrochemical one rou ghens the surface.