Electron spin resonance studies of various dehydrogenated (111)Si/(oxy)nitride structures, which had been grown at 1000 to 1150C in NH3, revealed the presence of 2 defects. The main one, PbN, was identified as being a Si dangling bond (•SiSi3) at the (111)Si/nitride interface which was aligned perpendicular to the interface. The use of X-ray photo-electron spectroscopy showed that  in situ  removal of the native Si oxide before nitridation was required in order to obtain stoichiometric Si3N4 films. The identification was based upon strong similarities (in g-matrix, location at the interface, line-width anisotropy) to the Pb defect at (111)Si/SiO2 interfaces. This detection of the •SiSi3 defect, at a natural Si/solid interface other than Si/SiO2, confirmed that Pb was a prototype dangling bond center, with its important characteristics being governed by the underlying Si matrix; not by the overlying insulator. On the other hand, the secondary electron spin resonance signatures differed when the large interface strain, which resulted from the greater rigidity of (oxy)nitrides as compared with SiO2 films, caused a slight perturbation of the Pb(N) symmetry; thus raising its C3v symmetry. This was confirmed, at 4.3K, by specific distortions of the PbN line shape. Upon increasing the temperature, the perturbation of the defect’s symmetry was smoothed due by thermally activated averaging over the various defect distortions. The properties of the Pb and PbN defects at higher temperatures tended to become identical. A comparison of unresolved 14N PbN and 17O Pb broadenings showed that their relative strengths agreed with known isotopic properties. A second defect, the intrinsic K center (•SiN3), with an isotropic g-value of 2.0028 was observed only in stoichiometric Si3N4 films.

A.Stesmans, G.Van Gorp: Physical Review B, 1995, 52[12], 8904-20