Thermal desorption spectroscopy and in situ reflection high-energy electron diffraction were used to investigate the surface structure and chemistry of (001) surfaces following wet chemical etching in dilute HF and NH4F solutions. The HF-etched surfaces were rough, and were terminated by mono-, di-, and tri-hydride species. The surface roughness which was observed after HF-treatment appeared to arise from surface defects such as adstructures and kinks which were left on the surface following removal of the oxide layers. The (001) etching in NH4F solution was found to be highly anisotropic, and the etching time was found the key parameter which determined the chemistry and morphology of the surface. It was shown that, for a limited etching time (about 60s), a flat and bulk-like dihydride-terminated (001) surface could be formed. This surface was found to transform, upon annealing under ultra-high vacuum, into a well-developed 2 x 1 reconstruction at temperatures as low as 400C. The results also suggested that (111) micro-facets were formed on (001) surfaces only after prolonged etching in NH4F solution, and remained stable up to about 650C.

Low-Temperature Formation of Si(001) 2 x 1 Surfaces from Wet Chemical Cleaning in NH4F Solution V.Le Thanh, D.Bouchier, G.Hincelin: Journal of Applied Physics, 2000, 87[8], 3700-6