Ordered Si(100) and (111) surfaces were prepared by chemical etching in solutions of hydrofluoric acid, and were studied by using soft X-ray photo-electron spectroscopy, X-ray photo-electron spectroscopy and low-energy electron diffraction. Despite being transferred through the open air before being loaded into an ultra-high vacuum, the hydrogen-terminated surfaces which were observed were among the most perfect then produced by such means. Under optimum conditions, etching could yield levels of carbon and oxygen impurities which were less than 2% of a monolayer, and led to surfaces where the Fermi level was not pinned. The etched surfaces were modified by the hydrogen termination, such that they were electrically passivated and ordered into a (1 x 1) periodicity. Upon annealing at 520C under ultra-high vacuum, the hydrogen was removed, the surface changed to a (2 x 1) reconstruction and also exhibited band bending due to Fermi-level pinning by surface states. The relationship was examined between residual contamination and etching parameters such as time and etchant concentration; together with the stability of the passivated surface under exposure to wet and dry environments. This showed that the surface condition was sensitive to the etching procedure, and that the optimum surface could be obtained by using a 5% non-aqueous solution or by pre-cleaning a surface using UV-generated ozone exposure before aqueous etching. It was shown that controlled re-oxidation of an etched surface, using UV-ozone could produce a non-abrupt Si/SiO2 interface.

An S/XPS Study of Hydrogen Terminated, Ordered Silicon (100) and (111) Surfaces Prepared by Chemical Etching. J.M.C.Thornton, R.H.Williams: Physica Scripta, 1990, 41[6], 1047-52