Initial stage of thermal oxidation of the Si(111)-(7×7) surface

Abstract

%e report a systematic study of the early oxidation process in a wide temperature range (20 -700'C) for the Si(111)-(7&7) annealed surface. Oxygen uptake data obtained by Auger-electron spectroscopy indicate that the surface oxygen uptake increases and then gradually saturates with 02 exposure at 20 C. At intermediate temperatures, there is no saturation and the oxygen uptake rate is enhanced. At 700'C, the uptake rate is enhanced in the high-exposure (or high-02-pressure} region, but is significantly reduced in the low-exposure region, presumably because of oxygen desorption as volatile SiO. Low-energy electron diffraction pattern transition from 7X7 to no pattern through a 1X1 intermediate pattern seems to be governed only by the amount of surface oxygen at any temperature, Using photoelectron spectroscopy we found that 02 exposures corresponding to this 1X1 pattern result in the disappearance of surface states centered about 0.6 eV below the valence-band maximum. A chemical-shift study of the Si 2p core level shows that not only the oxygen uptake rate, but also the way oxygen bonds to Si is strongly dependent on temperature. Our results show that at room temperature (20'C) all the Si atoms are oxidized at more or less the same rate, so that the adsorbed oxygen atoms are spread out uniformly over the entire Si surface. At high temperatures, certain Si atoms are being oxidized faster (i.e. , have more oxygen atoms bonded to them) than others, so that the distribution of adsorbed oxygen atoms is highly nonuniform; we find microscopic regions of Si02-like material interdispersed with regions of Si-like material. Therefore, in the early stage of oxidation, heating the substrate causes nonuniform oxidation with microscopic phase separation of Si02 and Si in the oxide film. Tight-binding calculations reported in the literature predict the oxygen 2p orbital to produce these valence states: 0 m (nonbonding}, 0 o (0 bonding), and 0 i (intermediate nature between nonbonding and 0 bonding). By studying the Oi -Op eak height ratio as a function of oxidation temperature and referring to theoretical calculations, we again come to the conclusion of nonuniform oxidation at high temperatures.

Investigation of submonolayer SiOX species formed from oxidation of silane on Pt(111)

“…Si-O-Si asymmetric vibrational modes shift from 950 cm À1 after small oxygen exposures to 1130 cm À1 after oxygen exposures corresponding to a full monolayer of oxidized Si species [39]. Garner and Tabe have used a basic model of sequential oxidation to explain the observed frequency shifts [14,40]. Initial Si-O bonds are atomic O atoms bound to surface Si atoms; additional oxidation occurs through O atoms being inserted between the first and second Si layers, causing surface Si atoms to be bound to 2-4 O atoms.…”

Direct observation of the layer-by-layer growth of initial oxide layers on Si(100) surface during thermal oxidation

“…The composition and structure of the transition region have been investigated previously. In particular, Grunthaner et ai [4], and subsequently others [5][6][7][8][9][10][11], found in Si 2/7 photoelectron spectra peaks attributed [4,5] to silicon atoms in different oxidation states, i.e., Si 14 ", Si 24 ", Si 34 ", and Si 44 ". The role of these states in oxide formation is still under discussion.…”

“…The first is connected with oxygen-atom accumulation at the interface. Silica growth is found [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16] to proceed by oxygen (rather than silicon) diffusion [17], with the silicon-oxide formation occurring at the Si-SiCh interface. This accumulation is accompanied by Si ,+ , Si 2+ -state formation.…”

“…The electron binding energy was measured with 0.1 -eV reproducibility. The oxidation kinetics was investigated directly in the analyzer chamber in a real-time regime [12], contrary to the usually used [6,13] restricted to the shoulder (see Fig. 1).…”

Kinetics of Initial Layer-by-Layer Oxidation of Si(001) Surfaces

“…Oxidation of Si surfaces is important for technological application of electronic devices [1][2][3]. Although many kinds of surface analyses have been used to study oxygen adsorption kinetics onto Si surfaces [4][5][6][7][8][9], the oxidation kinetics of subsurface layers, which determine oxide film growth, have not been studied in detail. This is because of the difficulty of experimentally and independently analyzing the oxidation processes of specific subsurface layers.…”