Structure of ultrathin SiO2/Si(111) interfaces studied by photoelectron spectroscopy

Abstract

Device-grade ultrathin ͑9-22 Å͒ films of silicon dioxide, prepared from crystalline silicon by remote-plasma oxidation, are studied by soft x-ray photoelectron spectroscopy ͑SXPS͒. The 2p core-level spectra for silicon show evidence of five distinct states of Si, attributable to the five oxidation states of silicon between Si 0 ͑the Si substrate͒ and Si 4ϩ ͑the thin SiO 2 film͒. The relative binding energy shifts for peaks Si 1ϩ through Si 4ϩ ͑with respect to Si 0 ͒ are in agreement with earlier work. The relatively weaker signals found for the three intermediate states (I 1 , I 2 , and I 3 ͒ are attributed to silicon atoms at the abrupt interface between the thin SiO 2 film and substrate. Estimates of the interface state density from these interface signals agree with the values reported earlier of ϳ2 monolayers ͑ML͒. The position and intensity of the five peaks are measured as a function of post-growth annealing temperature, crystal orientation, and exposure to He/N 2 plasma. We find that annealing produces more abrupt interfaces ͑by reducing the suboxide interface state density͒, but never more abrupt than ϳ1.5 monolayers. We observe a 15%-20% drop in the interface thickness ͑in particular the ''Si 2ϩ '' peak intensity͒ with increasing annealing temperature. Somewhat different behavior is observed with small amounts of nitrogen in the SiO 2 film where an apparent increase in interface state density is seen. A quantitative analysis is presented which explores the effects of these sample preparation parameters in terms of relative interface state density and modeling of the SXPS data.

Growth and Structure of Water on SiO2 Films on Si Investigated by Kelvin Probe Microscopy and in Situ X-ray Spectroscopies

“…32 Our surface potential measurements ( figure 3) show that up to ~20% RH the surface potential does not change appreciably, suggesting that for the first 1 to 2 monolayers the water molecules adsorb with their dipole moment either parallel to the surface or randomly oriented, in line with theoretical predictions. 11 At higher humidity, when 2 or more water layers are adsorbed, the average dipolar orientation changes and points towards the gas phase.…”

Ultra-thin silicon oxide layers on crystalline silicon wafers: Comparison of advanced oxidation techniques with respect to chemically abrupt SiO 2 /Si interfaces with low defect densities

“…As can be seen inFig. 3, the ratio of Si 1+ /Si 3+ fluctuates for the different samples, which is in accordance with models of oxide layer growth and can be explained by variations of the oxide thickness[52].3.2 Analysis of the electronic interface properties The quality of the chemical passivation of the structurally abrupt SiO 2 /Si interface was investigated by field-dependent surface photo voltage (SPV) measurements. SPV is a suitable and straightforward technique for deriving information on the SiO 2 /Si interface recombination behaviour.…”

Ultrathin SiO2 on Si IV. Intensity measurement in XPS and deduced thickness linearity

“…6. The angle-resolved work of Keister et al 11 shows the interface oxide states to be correctly below the SiO 2 layer. For oxides formed by deposition and other methods, the stoichiometry may not be as shown and extra layers may be involved.…”

“…These data are taken from our earlier work 8 on thermal SiO 2 where, prior to peak fitting, the Mg x-ray satellites have been removed, followed by removal of the 2p 1/2 spin-orbit split component, which is measured to be 50% of that of the 2p 3/2 peak and at 0.6 eV higher binding energy. After this, a Shirley background is removed and the peaks are fitted with five peaks representing the Si elemental peak together with four other peaks for SiO 2 10 and Keister et al 11 The binding energy of the SiO 2 peak shifts with the oxide thickness and, being an insulator, moves with the potentials of local charge control mechanisms. 12 The peak intensities lead to a value for d oxide as described later.…”