Ion beam effects in SiO x ( x

Abstract

The effect of low kinetic energy (0.5< E k<5 keV) Ar +, He + and N 2 + ion bombardment on non-stoichiometric silicon oxide SiO x ( x=1.3) thin films has been studied by X-ray photoemission spectroscopy, reflection electron energy loss spectroscopy and, for the case of the N 2 + bombarded samples, also by X-ray absorption spectroscopy at the O K and N K absorption edges. Thus, the composition of the altered layer of the bombarded material, as well as the chemical states of the elements in the samples have been determined. It has been found that preferential removal of oxygen takes place in SiO 1.3 after Ar + bombardment with ions of E k>2 keV. A detailed analysis of the Si 2p and Si KLL spectral shapes reveal that new Si + and, to a lesser extend, Si 4+ species are formed in detriment of the initial Si 3+ and Si + species present in the original SiO 1.3 sample. Bombardment with Ar + ions of lower kinetic energy ( E k<2 keV) produces the disproportionation of the SiO 1.3 material, mainly with formation of Si 4+ and Si + species, while the relative amount of Si 3+ decreases. By contrast with this behaviour, He + bombardment does not produce any significant reduction or disproportionation of the SiO 1.3 samples. These results reveal that both the kinetic energy of the impinging ions and the ability for transferring this energy to the target atoms are critical parameters for an effective control of the modifications induced in the bombarded samples. On the other hand, the “as-deposited” SiO 1.3 and the Ar + bombarded SiO 1.3 are characterised by bulk plasmon energies of 18.6 and 18.0 eV, and therefore, according to the free-electron theory, the density of these materials are 1.7 and 1.6 g/cm 3, respectively. In the case of the N 2 + bombardment, reactive implantation of nitrogen within the altered layer takes place with the formation of a new silicon oxynitride compound with the stoichiometry SiO 0.9N 0.6. The amount of incorporated nitrogen in this case is higher than that required to compensate the non-stoichiometry in the original SiO 1.3 material. This result indicates that preferential removal of oxygen also occurs under N 2 + bombardment. The formed silicon oxynitride is characterised by an Auger parameter of 1713.4 eV, with a band gap of 2–3 eV and a bulk plasmon energy of 21.9 eV.