Comparison of ultrathin SiO2∕Si(100) and SiO2∕Si(111) interfaces from soft x-ray photoelectron spectroscopy

The limitations of soft x-ray photoelectron spectroscopy (SXPS) for determining structural information of the SiO2∕Si interface for device-grade ultrathin (∼6–22Å) films of SiO2 prepared from crystalline silicon by remote plasma assisted oxidation are explored. The main focus of this article is the limitation of data analysis and sensitivity to structural parameters. In particular, annealing data shows a significant decrease in the integrated density of suboxide bonding arrangements as determined from analysis of SXPS data. These decreases and changes are interpreted as evidence for reorganization of specific interface bonding arrangements due to the annealing process. Moreover, these results suggest that sample preparation and processing history are both critical for defining the nature of the SiO2∕Si interface, and therefore its electrical properties. Quantitative estimates of the interface state densities are derived from SXPS data revealing ∼2 monolayers (ML) of suboxide as prepared and ∼1.5 ML of suboxide after rapid thermal annealing at 900°C for both Si(100) and Si(111) substrates. Comparison of the individual suboxide bonding state densities indicate for both Si substrate crystallographic orientations that annealing causes a self-organization of the suboxide consistent with bond constraint theory.