The Interaction of Fluorine and Oxygen with the (100) Surface of Silicon.

The interaction of fluorine and oxygen with the Si(100) surface has been examined under ultrahigh vacuum conditions with supersonic modulated molecular beam (MMB) techniques, X-ray photoelectron spectroscopy (XPS), quadrupole mass spectrometry, and low-energy ion scattering spectroscopy (ISS). The kinetics of adsorption has been examined as a function of both surface temperature and the average translational energy of the incident gas molecules. Molecular fluorine adsorbed dissociatively on the clean Si(100) surface. The initial probability was found to be essentially independent of both the incident beam energy and surface temperature. The coverage-exposure relationship for F_{rm 2} shows rapid adsorption to a coverage of 1.5 monolayers (ML). Subsequent adsorption is slower. The adsorption probability of atomic fluorine is weakly dependent on coverage. ISS measurements find no evidence for penetration of the silicon substrate by fluorine adatoms for coverages below 1.0 ML. Temperature-programmed decomposition of silicon -fluoride adlayers yielded SiF_{rm 2} and SiF_{rm 4 } as the only gas phase reaction products. In the range 0.3 to 1.0 ML, zero-order kinetics were found for the decomposition process. A qualitative assessment of the adlayer configuration following partial decomposition suggests that the thermal decomposition in the zero-order regime proceeds inhomogeneously. In the limit of very low fluorine coverages, MMB measurements indicate that the reaction that forms SiF_{rm 2}(g) follows second-order kinetics. Investigation of the steady-state reaction between F_ {rm 2}(g) and the Si(100) substrate for temperatures of 650-1200 K indicated conclusively that fluorine must be adsorbed dissociatively for the production of SiF_{rm 2}(g) to occur. Molecular oxygen adsorbed dissociatively on the clean Si(100) surface. The adsorption kinetics and separate ISS measurements indicated that the population of topmost surface sites diminished at elevated surface temperatures. The decomposition reaction has been examined with MMB techniques. SiO is the only gas phase reaction product, and the desorption of SiO occurred via a sequential two-step process above 1010 K, where the steady-state oxygen coverage was below 0.03 ML. For oxygen coverages above 0.7 ML, the desorption rate coefficient was orders of magnitude less. Decay of surface oxygen occurred exponentially in time for initial coverages of about 1 ML, but was more complex at higher coverages. (Abstract shortened with permission of author.).