Properties of the SiO2/SiC interface investigated by angle resolved studies of the Si 2p and Si 1s levels and the Si KLL Auger transitions

Angle resolved photoemission studies of the Si 2p and Si Is core levels and the Si KL2,3L2,3 Auger transitions from SiO2/SiC samples are reported. Most samples investigated were grown in situ on initially clean and well ordered root3 x root3 reconstructed 4H-SiC(0 0 0 1) surfaces but some samples were grown ex situ using a standard dry oxidation procedure. The results presented cover samples with total oxide thicknesses from about 5 to 118 Angstrom. The angle resolved data show that two oxidation states only, Si+1 and Si+4, are required to explain and model recorded Si 2p, Si Is and Si KLL spectra. The intensity variations observed in the core level components versus electron emission angle are found to be well described by a layer attenuation model for all samples when assuming a sub-oxide (Si2O) at the interface with a thickness ranging from 2.5 to 4 Angstrom. We conclude that the sub-oxide is located at the interface and that the thickness of this layer does not increase much when the total oxide thickness is increased from about 5 to 118 Angstrom. The SiO2 chemical shift is found to be larger in the Si Is level than in the Si 2p level and to depend on the thickness of the oxide layer. The SiO2 shift is found to be fairly constant for oxides less than about 10 Angstrom thick, to increase by 0.5 eV when increasing the oxide thickness to around 25 Angstrom and then to be fairly constant for thicker oxides. An even more pronounced dependence is observed in the Si KLL transitions where a relative energy shift of 0.9 eV is determined. The relative final state relaxation energy DeltaR(2p) is determined from the modified Auger parameter. This yields a value of DeltaR(2p) = -1.7 eV and implies, for SiO2/SiC, a "true" chemical shift in the Si 2p level of only approximate to0.4 eV for oxide layers of up to 10 Angstrom thick. (C) 2003 Elsevier Science B.V. All rights reserved.