Nitridation of a Si(100) surface by 100–1000 eV N+2 ion beams

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Abstract
The nitridation mechanism of silicon at room temperature under exposure to 100–1000 eV N+2 ion beams has been studied in situ in an ultrahigh vacuum apparatus using x-ray photoelectron spectroscopy. The increase of the nitrogen content in a surface layer as a function of the ion dose was described by a simple formula which was derived by assuming random occupation of the reaction sites in the penetration zone of the nitrogen atoms. A change of the binding energy and the width of the N1s x-ray photoelectron spectrum during the reaction was observed and discussed with the component ratio N/Sireacted. The Si2p x-ray photoelectron spectra were deconvoluted into five components of Si(0), Si(1), Si(2), Si(3), and Si(4) by curve fitting, where Si(n) represents the component of Si bonded to n nitrogen atoms. Their populations were dependent on the ion dose and the ion energy. The nitride layers formed in the Si surface with low energy beams of 100–200 eV had near-stoichiometric composition of Si3N4. With beams of energy higher than 300 eV, however, they were nonstoichiometric compounds SiNy (y<1.3) which were mixtures of those components. The influence of the beam energy was observed by the chemical shifts of the N1s and Si2p peaks at the saturation of the N content.