THE ROLE OF FLUORINE TERMINATION IN THE CHEMICAL-STABILITY OF HF-TREATED SI SURFACES

The principal role of silicon-fluorine bonds in the chemical nature of HF-etched Si surfaces has been investigated by angle-resolved X-ray photoelectron spectroscopy. The native oxide growth thickness and the fluorine coverage have been systematically measured as functions of HF concentration, pure water rinse time, air or N2 + O2 gas exposure time and gas phase H2O concentration. It is shown that the native oxide growth is strongly suppressed by the existence of Si-F bonds of about 0.12 monolayers on the surface. This is explained by a model in which Si-F bonds chemically stabilize the surface reactive sites such as atomic steps as supported by the result of the layer-by-layer oxidation of Si.