Characterization by x-ray photoelectron spectroscopy of the chemical structure of semi-insulating polycrystalline silicon thin films

Abstract

The x-ray photoelectron spectroscopy (XPS) technique has been used to investigate the composition of semi-insulating polycrystalline silicon (SIPOS) films having oxygen contents of 10 and 35 at. % prepared by low pressure chemical vapor deposition. XPS analysis has demonstrated that the film compositions can be qualitatively described by means of the five Si-SixO4−x tetrahedra (with 0≤x≤4 and integer) predicted by the statistical random bonding model (RBM). However, the quantitative analysis of the XPS spectra has demonstrated that the concentrations of the various tetrahedra found in the SIPOS films are remarkably different from those predicted by a statistical approach, i.e., by assuming that each Si atom forms with equal probability bonds with either Si or O. We have also found that the composition of high temperature (up to 1000 °C) annealed films further departs from that predicted by the RBM model; indeed, the anneal promotes the decomposition of partially oxidized Si-SixO4−x tetrahedra in Si-Si4 tetrahedra (that form Si nanocrystals) and Si-O4 tetrahedra (that enrich the oxygen content of the amorphous phase).

Room temperature nanocrystalline silicon single-electron transistors

“…21 It is also reported that thermal annealing converts a partially oxidized SiϪSi n O 4Ϫn (nϽ4) tetrahedral structure to SiϪO 4 tetrahedral structure, confirmed by x-ray photoelectron spectroscopy. 22 On the other hand, there remain silicon rich phases (SiϪSi n O 4Ϫn ) after the thermal annealing at 1000°C.…”

Control of grain-boundary tunneling barriers in polycrystalline silicon

“…In addition, such suboxide structures can persist even at 1000°C. 13 We suggest that the GBs are a mixture of Si-O 4 and silicon-rich structures, the former with an energy gap close to silicon dioxide and the latter with a lower energy gap. These energy gaps and the local trapped charge create potential barriers at the GBs, and a mix of these structures leads to a local distribution in V B .…”

“…This has been observed in silicon suboxide, where the silicon-rich bonding structure Si-Si 4Ϫn O n (nϽ4) forms the major portion of the suboxide. High-temperature annealing can convert some parts of this to a Si-O 4 tetrahedral structure 13 or cause phase separation into nanocrystalline silicon and silicon dioxide. 14 In our films, the GB volume may be limited for nanocrystalline silicon formation, and a Si-O 4 structure may form locally.…”

Effect of oxidation on charge localization and transport in a single layer of silicon nanocrystals

“…The peak located at 103.8 eV is the signature peak for Si bonded to four O atoms (SiO 2 ) whereas the peak located at 99.3 eV corresponds to a Si atom tetrahedrally bonded to four Si atoms. 22 Because the nanocrystal layer is separated from the substrate by 25 nm thick SiO 2 , the entire signal at 99.3 eV originates from Si in the nanocrystals and the contribution from the c-Si substrate is negligible. With increasing oxidation duration, the peak at 99.3 eV reduces and the peak at 103.8 eV increases indicating consumption of Si in the nanocrystal layer and formation of SiO 2 .…”

“…The SiO 2 formed during the oxidation process is stoichiometric since no shoulders or peaks ͑in the region between 100 and 103 eV͒ attributable to the presence of SiO x (xϽ2) suboxides are observed. 22 Figure 7͑a͒ shows the ⌬͑͒ image recorded prior to charging the 30 min oxidized nanocrystal layer. The ⌬͑͒ image obtained 12 min after charging the nanocrystals is shown in Fig.…”