Influence of Si oxidation methods on the distribution of suboxides at Si/SiO2 interfaces and their band alignment: a synchrotron photoemission study

The quality of oxide/semiconductor interfaces becomes of major importance when the insulating layer is thinner than 5 nm, as is the case in state-of-the-art microelectronics. In this work, we characterize with high resolution synchrotron photoemission the structure formed between SiO2 layers of different thickness and Si substrates with (1 0 0) and (1 1 1) orientation. Three different oxidation methods are considered: (i) thermal oxidation in the presence of molecular oxygen, (ii) thermal oxidation with excited oxygen, and (iii) electron stimulated oxidation at room temperature. The oxidation method affects the interface stoichiometry, the most abrupt interfaces being obtained by thermal oxidation without electrons. The SiO2 chemical shift is always ∼0.1 eV larger for the Si(1 0 0) orientation compared to the Si(1 1 1), as corresponds to a larger valence band offset. Direct comparison of the Si–SiO2 chemical shift with the work function variations does not support a charging mechanism as responsible for the Si4+ energy shift increase.