Reactions of Atomic Oxygen with Si(100) and Si(111): 2. Adsorption, PassiveOxidation and the Effect of Coincident Ion Bombardment

摘要

The reactions of atomic oxygen with the (100) and (111) surfaces of silicon havebeen investigated by employing supersonic molecular beam techniques. X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering spectroscopy (ISS). Atomic oxygen adsorbs with unit probability on the clean silicon surface, independent of substrate temperature (110-800 K) and incident mean translational energy (3-16 kcal mol-1). Oxidation of clean silicon with an oxygen atom beam is characterized by two stages: a 'fast' stage that corresponds to oxygen chemisorption in the topmost 2-3 silicon layers; and a 'slow' stage that corresponds to oxygen incorporation and oxide film growth. The chemisorption stage is described by first-order Langmuirian kinetics with an apparent saturation coverage of approximately 4 ML O(a), the oxide growth stage by 'direct' logarithmic kinetics, where dx/dt = alpha exp(-x/L), where x is the oxide thickness. Observation of significant oxidation at substrate temperatures of 110 K suggests that oxide growth in the slow stage may occur by a field-assisted mechanism, where an internal electric field aids transport of oxygen to the underlying silicon substrate layers.