THERMAL-DECOMPOSITION OF VERY THIN OXIDE LAYERS ON SI(111)

We investigate the thermal decomposition and desorption of very thin oxide layers prepared on Si (111) by oxygen adsorption as well as by chemical treatments. The oxides are examined by Auger electron spectroscopy, thermal desorption spectroscopy, and atomic force microscopy. The decomposition mechanism changes drastically at an oxide thickness of approximately 6 angstrom; the decomposition temperature depends on the formation method for oxides thicker than 6 angstrom, but the dependence disappears for oxides thinner than 6 angstrom. The former result can be qualitatively interpreted by the difference in SiO diffusivity between the oxides. The latter suggests that the decomposition rate is governed by reactions at the oxide/Si interface because the oxide layer is so thin that diffusion is not the dominant factor. The possibility of thermally removing the thin oxide layer in a dry oxygen/Si system for layer-by-layer etching or "monolayer peeling" is also discussed.