Silicon Suboxide Research Articles

Fabrication of SiO2 Phase Gratings by UV Laser Patterning of Silicon Suboxide Layers and Subsequent Oxidation

UV transparent phase masks are used in various laser applications like fabrication of Bragg gratings in optical fibers or micro patterning by high power laser ablation. Normally they are fabricated by a costly lithographic process including e-beam writing and reactive ion etching. We propose a new fabrication method based on UV laser ablation. The process consists of three steps. First, a silicon suboxide coating (SiOx with x < 2) with a predefined thickness is deposited on a fused silica substrate. Second, due to its strong UV-absorption, this coating can be removed in defined areas by excimer laser ablation at 193 nm or 248 nm leading to the desired phase pattern in form of a binary depth profile. Third, by applying a thermal annealing process, the remaining SiOxcoating is oxidized to UV-transparent SiO2, resulting in a UV-grade surface relief element. The precisely defined interface between substrate and layer allows for ablation with exact depth control and perfect optical surface quality. Such SiO2 phase masks feature a large processed area, high efficiency for VUV to NIR radiation and can be customized e.g. for perfect zero order suppression. Applications of such phase gratings for materials processing with a UV-femtosecond laser are demonstrated. Using the phase gratings in a mask projection configuration, submicron patterns are created in a variety of materials.

Investigations of the electron energy structure and phase composition of porous silicon with different porosity

Energy structure of the valence and conduction bands together with phase composition of porous silicon (por-Si) obtained at different etching times were investigated using ultrasoft X-ray emission spectroscopy (USXES) and X-ray absorption near-edge structure (XANES) techniques. USXES and XANES spectra represent local partial density of states in valence and conduction band, correspondingly. XANES data were obtained with the use of synchrotron radiation at synchrotron BESSY II. Porous silicon layers were obtained on different types of single-crystalline silicon (1 0 0) and (1 1 1) substrates by standard electrochemical etching in HF solution with etching times from 1 to 10 min. USXES and XANES investigations show formation of Si nanocrystals covered by amorphous phase together with nonstoichiometric silicon sub-oxide SiO x ( x ∼ 1.3) in the surface layers. XANES investigations show that the increase of sample porosity leads to the shift of conduction band edge to the higher energy range that corresponds to increase of the band gap width in porous silicon up to ∼1.4 eV.

Structures and Properties of Silicon Oxide Clusters by Theoretical Investigations

In this paper, we outline our computational work in the area of silicon oxide clusters. To reduce the computational cost, we designed an economic basis set for silicon oxide systems, and reliable structures were obtained by this approach. To reveal the formation mechanism of silicon nanowires, we investigated the structures and properties of silicon suboxide clusters in particular monoxide clusters that play an important role in the oxide-assisted growth. And to improve our understanding of the silicon dioxide clusters and to bridge the gap between gas phase and solid phase silica, we proposed several models based on the two-membered ring (2MR), three-membered ring (3MR), four-membered ring (4MR), the hybrid of the 2MR and 3MR, or the 3MR and 4MR.

Periodic chains of gold nanoparticles and the role of oxygen during the growth of silicon nanowires

The introduction of oxygen during silicon monoxide–vapor liquid solid growth of silicon nanowires causes a shift in silicon suboxide stoichiometry resulting in an increased formation of silicon dioxide at the nanowire surface. This leads to instabilities of the usual cylindrical nanowire core-shell structure, where the liquid gold/silicon alloy droplet at the nanowire tip is incorporated inside a silicon dioxide nanowire to form a periodic array of nanoparticles. The structure and the composition of the resulting nanostructure are investigated using transmission electron microscopy. The influence of the oxygen is investigated experimentally and supports the authors’ model of the formation mechanism.

Computational Design of Silicon Suboxides: Chemical and Mechanical Forces on the Atomic Scale

Silicon suboxides play an important role in different industrial applications, particularly in the form of the Si–SiO2 interface, which is one of the key elements in present day microelectronics and potentially in future nano-electronics as well. This paper focuses on the chemical and mechanical effects related to the existence of different oxidation states of Si atoms in SiO x systems with various Si:O composition and topology, such as O atoms in Si, the Si–SiO2 interface, and O vacancies in SiO2. We compare the stress–strain relation in SiO2 interfaces with (100), (111) and (110) surfaces, the relative stability of oxygen vacancies at different locations in Si–SiO2 layers and defects in Si and SiO2 crystals related to O migration. Our study is based on ab initio computations of molecular and periodic systems with both localized and plane wave basis sets.

Surface morphology and reaction at Cu/Si interface—Effect of native silicon suboxide

Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu 3Si and Cu 4Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites.

Post-annealed silicon nanocrystal formation on substoichiometric SiOxNy(x&lt; 2,y&lt; 1) layers deposited in SiH4-N2O radiofrequency discharges

In this work is presented a detailed physicochemical, structural and optical characterization of SiO x N y thin films. The films deposited using PECVD in SiH 4 -N 2 O-He discharges were thermally annealed at 1273 K for 1 hour in ambient nitrogen. The film stochiometry was measured by Rutherford Backscattering Spectroscopy. The chemical composition was dominated by silicon suboxide containing some Si-N and Si-H bonds. Raman scattering measurements suggest the formation of nanocrystallite silicon in the annealed films. The Raman observation is strongly supported by Transmission Electron Microscopy analysis which shows a high density of silicon nanocrystals, having a mean radius ranging between 3 and 6 nm. Using Spectroscopic Ellipsometry, we discussed the dielectric function evolution as a function of the deposition parameters.

Computational design ofSi∕SiO2interfaces: Stress and strain on the atomic scale

In this paper, we present results of a comparative computational study of silicon oxide interfaces with (100), (111), and (110) silicon surfaces. Density functional theory (DFT) in the local density approximation (LDA) and generalized gradient approximation with plane wave basis set and in the LDA approximation with localized numerical atomic orbitals are applied to investigate the relation between the structure and topology of chemical bonds and stress and strain effects at different $\mathrm{Si}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ interfaces, which play a crucial role in electronics materials and devices. The resulting stress energies are discussed in terms of chemical, mechanical, and electric polarization components. According to our observations, chemical and mechanical components in the interface energy are not sufficient for description of silicon suboxide systems including $\mathrm{Si}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ interfaces and the long range electrostatic interactions provide a non-negligible contribution. We uncovered computationally an effect of thermodynamic stabilization of oxygen incorporation in silicon lattice, which may have potential implications for nanoscale electronic device design. The trends in the stress energies derived from the results of the calculations are independent from the DFT approaches applied in this study.

Controlling defect and Si nanoparticle luminescence from silicon oxynitride films with CO2 laser annealing

We demonstrate that a focused CO2 laser beam (λ=10.6μm) can be employed to locally synthesize light emitting defects and Si nanoparticles in silicon rich oxynitride thin films. Films with a stoichiometry of SiO1.08N0.32 were prepared by plasma enhanced chemical vapor deposition with N2O and SiH4. Strongly absorbing CO2 laser light was then used to induce local heating in the films in air ambient using power densities in the range from 0 to 580W∕cm2 and times of 5s to 60min. High-resolution cross sectional transmission electron microscopy (TEM) images of the irradiated region revealed the presence of crystalline Si nanoparticles. Photoluminescence (PL) spectra taken from irradiated areas showed two distinct peaks around 570 and 800nm. From a combined TEM, Rutherford back scattering (RBS), forming gas annealing (FGA), PL, and PL lifetime study it is concluded that the 570nm peak with a short PL lifetime (&amp;lt;10ns) is related to defects characteristic of silicon suboxides and that the 800nm peak is due to exciton recombination inside the Si nanoparticles. The appearance of an isosbestic point in the PL spectra suggests that upon CO2 laser heating Si nanoparticles are formed at the expense of the luminescent defect structures, which are annealed out.

Si nanocrystal-containing SiO x ( x < 2) produced by thermal annealing of PECVD realized thin films

This paper is focused on the description of relationship between deposition parameters (flow rates of SiH 4 and N 2O precursor gases) and properties of SiO x films. The silicon-rich silicon oxide thin films deposited using plasma enhanced chemical vapour deposition (PECVD) in silane-nitrous oxide-helium discharges were thermally annealed at 1273 K for 1 h. Fourier transform infrared (FTIR) spectroscopy indicated that the chemical composition was dominated by silicon suboxide containing silicon-nitride and silicon-hydrogen bonds. For the as-deposited films and for the annealed films, Raman spectra show a band approximately at 480 cm −1, related to amorphous silicon and a band at 520 cm −1, related to nanocrystallite silicon, respectively. Transmission electron microscopy analysis demonstrated that silicon nanocrystals (Si nc), having a mean radius ranging between 3 and 6 nm were present in the annealed films. Using spectroscopic ellipsometry (SE) in the 0.2–0.88 μm spectral range, the values of layer thickness, optical indices and component volume fractions were determined using the Fourouhi–Bloomer (FB) model for the as-deposited films and the Bruggeman effective medium approximation (BEMA) for the annealed ones.

Interaction between the silyl and silylen centres in the deposits prepared by pulsed laser ablation of silicon monoxide and ammonia, methylamine and dimethylamine

Silicon suboxide films were prepared by TEA CO2 pulsed laser ablation (PLA) of the silicon monoxide target in the Kr atmosphere. The deposits were examined by means of Fourier transformed infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR) and X-ray photoelectron spectroscopy (XPS). The generated point defects in the films – mostly silyl ≡Si· (E’ center) and silylen =Si: – were allowed to react with the gaseous ammonia NH3, methylamine MeNH2 and dimethylamine Me2NH after the ablation. As a result, the functional groups ≡SiNHxMey (x+y=2) were formed. The reactivity of the deposits are due to silyl ≡Si· and silylen =Si: radicals as deduced by comparison of the initial concentration of the silyl radicals (5.3–9.8×1019 /g, EPR) – and the newly formed -(Si)NH bonds (3.6×1019 /g, FTIR). The observed absorption bands ν(SiH) at 2223, 2214 and 2220 cm-1 could be assigned to =(O2)Si(H)NH2, =(O2)Si(H)NHMe and =(O2)Si(H)NMe2 species. The singlet line in EPR spectrum of the native deposit before exposition is due to the silyl radical with free valence on the silicon backbonded via oxygen and another silicon atom. After exposition either to NH3 or MeNH2 the silyl concentration rapidly decreased to several % of its original value.

On-line characterisation of radiofrequency magnetron sputter deposition of SiO x using elastic recoil detection

A radiofrequency Ar/O 2 magnetron discharge is used to deposit silicon suboxide (SiO x , 0 ≤ x ≤ 2) films. In this paper we demonstrate how we can apply the high-energy ion beam technique elastic recoil detection (ERD) on-line, i.e. in situ during deposition, to continuously monitor the growing layer thickness and depth resolved composition. From the ERD data the deposition rates of distinctly silicon and oxygen and the composition of the growing film are determined. Using this method several growth conditions can be investigated and compared in a fast and reliable manner on a single substrate. In this work we report the variation of the growth rate and of the composition of the growing layer as a result of the variation of the rf power and show the consequence of keeping the O 2 flow constant in comparison to keeping the O 2 partial pressure constant.

Electronic Sputtering of Silicon Suboxide Films by Swift Heavy Ions

Two regimes are discerned experimentally in the electronic sputtering of silicon suboxide (SiO{sub x}) films under irradiation with 50 MeV Cu ions. For x<1 the removal rate is low and increases with x; for 1.5<x<2 the removal rate is high and about constant [(1.6-2.0)x10{sup 3} atoms per incoming ion]. The transition occurs at x values where the electronic structure of SiO{sub x} has a transition. We propose a model, which connects the electronic sputter rate with the SiO{sub x} electronic structure considering the lifetime of the ion track.

High-energy ion-beam-induced phase separation inSiOxfilms

The modification of the nanostructure of silicon suboxide $(\mathrm{Si}{\mathrm{O}}_{x})$ films as a result of high-energy heavy-ion irradiation has been studied for the entire range $0.1\ensuremath{\leqslant}xl2$. The $\mathrm{Si}{\mathrm{O}}_{x}$ films have been obtained by radio-frequency magnetron sputter deposition. For $50\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ $^{63}\mathrm{Cu}^{8+}$ ions and an angle of incidence of 20\ifmmode^\circ\else\textdegree\fi{} with the plane of the surface, and for $x\ensuremath{\geqslant}0.5$, it takes a fluence of about ${10}^{14}∕{\mathrm{cm}}^{2}$ to reach a $\mathrm{Si}\text{\penalty1000-\hskip0pt}\mathrm{O}\text{\penalty1000-\hskip0pt}\mathrm{Si}$ infrared absorption spectrum, which is supposed to be characteristic for a $\mathrm{Si}\text{\penalty1000-\hskip0pt}\mathrm{Si}{\mathrm{O}}_{2}$ composite film structure. For smaller $x$ values, it takes a much larger fluence. The interpretation of the IR spectra is corroborated for the surface region by results from x-ray photoelectron spectroscopy. The results present evidence for a mechanism, in which the phase separation takes place in the thermal spike, initiated by the energy deposited in many overlapping independent ion tracks. Such a process is possible since the suboxides fulfill the conditions for spinodal decomposition.

Control of silicidation in HfO2∕Si(100) interfaces

The interfacial states of the HfO2 thin film grown on the Si(100) substrate by the pulsed laser deposition method is investigated in situ using x-ray photoelectron spectroscopy. They are found to depend on the HfO2 film thickness, oxygen pressure during the pulsed laser deposition growth, and the deposition process. The hafnium silicide is formed in an oxygen-deficient condition, and it can be most effectively controlled by the ambient oxygen pressure during film growth. The close relation between the silicide formation and abundance of the silicon suboxides at the interface is presented.

Correlation between Er 3+ emission and Si clusters in Erbium-doped a-SiO x:H films

Erbium-doped hydrogenated amorphous silicon suboxide films containing silicon clusters (a-SiO x :H) were prepared. The samples exhibited photoluminescence (PL) peaks at around 750 nm and 1.54 μm, which could be assigned to the electron–hole recombination in silicon clusters and the intra-4f transition in Er 3+, respectively. We compared annealing behaviors of Si clusters and Er 3+ emission and found that Si clusters emission depends strongly upon crystallinity of Si clusters, whereas Er 3+ emission is not sensitive to whether it is Si nanocrystals (nc-Si) or amorphous Si (a-Si) clusters. The erbium-doped a-SiO x :H films containing either a-Si clusters or nc-Si have the same kind of Er 3+-emitting centers. Based on these results, it is concluded that a-Si clusters can play the same role on Er 3+ excitation as nc-Si.

Characterization of Si-Based Nanoparticulates Produced by Carbothermic Reduction of Silica-Containing Slag

Si-based nanoparticles, nanochains and nanowires were synthesized by smelting reduction method which includes a high temperature carbothermic reduction of silica-rich melt to SiO vapor and transfer of the vapor with Ar carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. Features of the process have been discussed in our previous paper. In this paper, the synthesized nanoparticulates were characterized by using XRD, XPS, EDX, TEM and HRTEM analysis. The deposition temperature was found to be the crucial parameter governing the nanoparticulate morphology and phase composition. The nanowires were obtained in the high temperature range of 1320–1570 K. It is found that the as-obtained nanowires were composed of a SiC core and an amorphous sheath of silicon suboxide. The nanowires had diameter ranging from 20 to 60 nm and length up to several microns. The rounded nanoparticles of 30–50 nm in diameter were deposited at locations under temperatures lower than 920 K. They were mainly composed of amorphous silicon suboxide which could be decomposed under certain conditions yielding Si nanocrystallites embedded into the oxygen enriched suboxide matrix. The nanocrystallite size was estimated to be of 3–8 nm although much larger, up to 50 nm, Si crystals were detected at high temperature locations.

マグネトロンスパッタリング法により作製した傾斜機能亜酸化けい素膜の放射冷却特性

Silicon suboxide (SiOx) could be a potential material for radiative cooling due to appropriate infra-red absorption at wave-length (λ) between 8 and 13 μm. In this study, SiOx films ranging from x=0.98 to 1.7 were prepared by magnetron sputtering using a SiO sintered body target. An SiO0.98 single layer film had a relatively sharp absorption peak at λ=10 μm. The obtained SiO0.98 film showed amorphous and a black-brown color. An optical band gap (Eg) of the SiO0.98 film was 3.6 eV, and the SiOx (x>1.4) film was transparent in the UV-visible range with a wide optical band gap (>4 eV). A functionally graded SiOx layers showed broader absorption from λ=8 to 13 μm, promising for radiative cooling.

In situ x-ray photoelectron spectroscopic and density-functional studies of Si atoms adsorbed on a C60 film

The interaction between C(60) and Si atoms has been investigated for Si atoms adsorbed on a C(60) film using in situ x-ray photoelectron spectroscopy (XPS) and density-functional (DFT) calculations. Analysis of the Si 2p core peak identified three kinds of Si atoms adsorbed on the film: silicon suboxides (SiO(x)), bulk Si crystal, and silicon atoms bound to C(60). Based on the atomic percent ratio of silicon to carbon, we estimated that there was approximately one Si atom bound to each C(60) molecule. The Si 2p peak due to the Si-C(60) interaction demonstrated that a charge transfer from the Si atom to the C(60) molecule takes place at room temperature, which is much lower than the temperature of 670 K at which the charge transfer was observed for C(60) adsorbed on Si(001) and (111) clean surfaces [Sakamoto et al., Phys. Rev. B 60, 2579 (1999)]. The number of electrons transferred between the C(60) molecule and Si atom was estimated to be 0.59 based on XPS results, which is in good agreement with the DFT result of 0.63 for a C(60)Si with C(2v) symmetry used as a model cluster. Furthermore, the shift in binding energy of both the Si 2p and C 1s core peaks before and after Si-atom deposition was experimentally obtained to be +2.0 and -0.4 eV, respectively. The C(60)Si model cluster provides the shift of +2.13 eV for the Si 2p core peak and of -0.28 eV for the C 1s core peak, which are well corresponding to those experimental results. The covalency of the Si-C(60) interaction was also discussed in terms of Mulliken overlap population between them.

Influence of oxidant source on the property of atomic layer deposited Al 2O 3 on hydrogen-terminated Si substrate

Al 2O 3 thin films were deposited on hydrogen-terminated Si substrate using atomic layer deposition (ALD) technique with tri-methylaluminum (TMA) and an oxidant source of H 2O vapor, O 2 plasma, or O 3. Substrate temperature was maintained at 350 °C when the Al 2O 3 films were grown with the oxidant sources of H 2O vapor and O 3, and with the oxidant source of O 2 plasma, Al 2O 3 films were deposited at the substrate temperature of 200 °C. Growth rates of Al 2O 3 films on HF-cleaned Si surface were saturated at 0.08, 0.14, and 0.06 nm/cycle for H 2O vapor, O 2 plasma, and O 3, respectively. Equivalent oxide thickness (EOT) and leakage current vs. physical thickness of atomic layer deposited Al 2O 3 films grown with various oxidant sources were also measured in this study. To investigate the main cause of different EOT with oxidant sources, interfacial properties were examined by using transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). In the TEM analysis, interfacial layers with the thickness of about 1.7 and 1.3 nm were observed in as-deposited Al 2O 3 films grown using O 2 plasma and O 3. We confirmed that the interfacial layers were mainly composed of SiO x in the XPS depth analysis. Using angle resolved X-ray photoelectron spectroscopy, effect of annealing on the interfacial structure of Al 2O 3 films grown with O 3 and O 2 plasma was also studied, and we found that after annealing, the peak corresponding to silicon suboxide and Al-silicate disappeared and fully oxidized Si 4+ increased.