The nitridation mechanism of silicon at room temperature under exposur
e to 100-1000 eV N-2(+) ion beams has been studied in situ in an ultra
high vacuum apparatus using x-ray photoelectron spectroscopy. The incr
ease of the nitrogen content in a surface layer as a function of the i
on dose was described by a simple formula which was derived by assumin
g random occupation of the reaction sites in the penetration zone of t
he 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/Si-reacted. The Si2p x-ray photo
electron 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 th
e component of Si bonded to n nitrogen atoms. Their populations were d
ependent 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-stoich
iometric composition of Si3N4. With beams of energy higher than 300 eV
, however, they were nonstoichiometric compounds SiNy, (y<1.3) which w
ere mixtures of those components. The influence of the beam energy was
observed by the chemical shifts of the N1s and Si2p peaks at the satu
ration of the N content.