ETCHING OF SILICON IN NAOH SOLUTIONS .1. INSITU SCANNING TUNNELING MICROSCOPIC INVESTIGATION OF N-SI(111)

The etching of n-type silicon (111) has been investigated by means of in situ scanning tunneling microscopy (STM) observations performed ove r a wide range of bias of the sample. A special procedure has been use d to observe topography changes at potentials close and positive of th e rest potential. Irrespective of the bias, images show that the surfa ce consists in atomically smooth terraces separated by 3.1 angstrom hi -gh steps. At cathodic bias, the etching occurs principally at terrace edges and (111) terraces are most probably H terminated, which preven ts their reconstruction, as could be seen in atomically resolved pictu res taken in situ. Triangular etch pits nucleate when the potential ap proaches the rest potential. The Si-H coverage is, however, preserved despite the continuous removal of Si atoms from the surface. Beyond th e passivation potential, a high density of etch pits is developed on t he terraces, although the dissolution rate decreases. It is shown that the etch rate of the dissolution can be derived from sequences of STM images and that it presents a maximum, close to the rest potential, a s it has been found previously with long-term material loss measuremen ts. The present STM results yield new insights into the surf ace chemi stry and the anisotropy of the reaction. The complementary electrochem ical characterization of the etching process will be outlined in Part II of this paper (the following article) where a detailed reaction mec hanism is presented.