USE OF MULTILAYER TECHNIQUES FOR XPS IDENTIFICATION OF VARIOUS NITROGEN ENVIRONMENTS IN THE SI/NH3 SYSTEM

The experimental ability to reach rapidly, under UHV and on the same substrate holder, the high temperatures (1100 K) required for silicon surface reconstructions and the low temperatures (80 K) needed to condense ammonia molecularly or to adsorb this gas dissociatively on specific silicon surface states, allowed us to elaborate thin multilayers made up of various combinations of the nitrogen chemical environments involved in the Si/NH3 system. Included in a surface layer (< 50 angstrom) corresponding to the analysing electron escape depth of a X-ray photoelectron spectrometer, they lead one to obtain the binding energy signatures for molecular ammonia (NH3), amide (NH2) and imide (NH) fragments and nitrides (Si3N) by simultaneously and easily comparable N 1s core level recordings. The results confirm that beside the T(s) dependence of the degree of dissociation of NH3, the silicon surface state configuration (Si(100)-2 x 1, Si(111)-7 x 7, a-Si) is another important parameter explaining the presence of differently adsorbed N, NH or NH2 groups.