Interactions of ion beams with surfaces. Reactions of nitrogen with silicon and its oxides

Ion beam studies of chemical reactions between nitrogen and surfaces of silicon and its oxides are reported. A spectrometer system designed for these studies which combines the techniques of x-ray and uv photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectroscopy, low energy electron diffraction, and ion bombardment is described. This work employs XPS and UPS to examine the products induced by 500 eV N+2 beams on targets of elemental Si, SiO, and SiO2. The N+2 ions undergo charge exchange and dissociation at the surface of the target to form hot N atoms. Reaction with Si, produces nitrides which are similar to those of the type Si3N4. Reaction with SiO and SiO2 forms nitrides, with no evidence of nitrate or nitrite formation. The chemical nature of the reaction is suggested by identification of the reaction products through XPS and UPS and energy level shifts. The thickness of the silicon nitride layer on Si(111) formed by 500 eV N+2 bombardment has been determined to be ∼19 Å thick by using the film/bulk Si XPS intensity ratio. Estimates obtained by depth-concentration profiling with 1 keV Ar+ and by using LSS projected ion range calculations agree with this approximate thickness.