Si-OH Bonds Research Articles

The Structure Change of Liquid Phase Deposited Silicon Oxide by Water Dilution

The silicon oxyhydrogen (Si‒OH) bonds were found in large amounts in conventional liquid‐phase‐deposited silicon dioxide using silica powder or gel as a saturation reagent in hydrofluorosilicic acid . However, a more dense structure of LPD‐ devoid of Si‒OH bonds was found if the reagent is changed to silicic acid and the concentration of is kept above 2 M. At 30°C, the water dilution of from 2.5 to 1 M tends to enhance the deposition rate of silicon oxide and to introduce substantial amount of Si‒OH bonds into the film when concentration drops to below 1.5 M. This is attributed to the fact that water dilution tends to dilute the concentration of all components but the decay of etching rate of by HF is much faster than the growth rate of , because the removal of one silicon needs more HF molecules (from one to four HF) and the growth of one silicon needs only one intermediate species. The growth rate of silicon oxide decreases when concentration is further lowered to 0.5 M. The delay time during initial oxide growth follows the growth rate, it is concluded that the delay time is the time that the solution needs to modify part of the Si‒OH or Si‒H bonds on the growth surface of to Si‒F bonds by hydrofluoric acid (HF).

Photoluminescence from mechanically milled Si andSiO2spowders

The photoluminescence (PL) in as-received and milled Si and SiO2 powder is reported. The Si and SiO2 powder is characterized by chemical analysis, Raman scattering, x-ray photoelectron spectra, infrared absorption, x-ray diffraction, and differential thermal analysis. The results indicate that the Si powder has amorphous Si oxide and suboxide surface layers. The milling of Si powder results in the formation of nanocrystalline/amorphous Si components. An amorphous SiO2 component is formed by milling crystalline SiO2. The PL spectra for as-received Si, milled Si, and SiO2 powder exhibit similar peak shapes, peak maxima, and full width at half maximum values. For both the as-received and the milled Si powder, experimental results appear to exclude mechanisms for PL related to an amorphous Si component or Si-H or Si-OH bonds, or the quantum confinement effect. Similarly, for milled SiO2 powder mechanisms for PL do not appear related to Si-H or Si-OH bonds. Instead the greatly increased intensity of PL for milled SiO2 can be related to both the increased volume fraction of the amorphous SiO2 component and the increased density of defects introduced in the amorphous SiO2 upon milling. It is suggested that the PL for as-received Si, milling-induced nanocrystalline/amorphous Si, and milled SiO2 results from defects, such as the nonbridging oxygen hole center, in the amorphous Si suboxide and/or SiO2 components existing in these powder samples. The PL measurement for milled SiO2 is dependent on air pressure whereas that for as-received SiO2 is not, suggesting that new emitting centers are formed by milling.

Monitoring of the thermal annealing of HDP-Si oxides by positron annihilation and thermal desorption spectrometry

The thermal annealing of 1.5 μm thick SiO 2 layers deposited on Si with a High Density Plasma (HDP) has been monitored by Thermal Desorption Spectrometry (TDS), Fourier Transform Infra-Red absorption (FTIR) and Positron Annihilation Doppler Broadening (PADB). Two samples were prepared with different production conditions (substrate temperature, Ar flow, ratio) in order to get oxide layers rich in SiH bonds or rich in SiOH bonds. The deposition temperatures of these layers were 545 K and 575 K, respectively. The formation of SiH rich and SiOH rich oxides was confirmed by FTIR absorption measurements. Desorption measurements showed that at a heating rate of 5 K/s release of hydrogen takes place around 1100 K. For the layer deposited at 575 K additional release of hydrogen is observed at 900 K. In both samples argon release is seen around 1200 K. The release of hydrogen at 1100 K is consistent with FTIR measurements at annealed samples. The absorption peaks associated with the SiH and SiOH bonds only disappear after heating above 1000 K. For the PADB measurements thermal anneals were carried out from 300 to 1300 K in steps of 50 and 100 K of 16 min duration. The positron measurements show different annealing behavior of the two oxides. It is observed that up to 1200 K the 545 K oxide shows a significant higher value for the defect parameter. The argon and hydrogen release is observed by an increase of the defect parameter at 1000 K.

First-Principles Study Of Photoluminescence From Silicon/Silicon-Oxide Interfaces

AbstractExperimentally reported interfacial luminescence from silicon nano structures are studied by using a first-principles calculation of a Si(100) quantum slab covered with silicon oxide. When Si-OH bonds were introduced at the silicon/silicon-oxide interface, wave functions at the valence band top and near conduction band bottom localized vertically and laterally near the Si-OH bonds. Such strong localization is the result of the cooperation of the coupling of non-bonding 2p lone pair orbitals on interfacial 0 atoms and the strong dipole of OH. Furthermore, the localization is significant only in silicon nano structures. This localization of the wave functions can be the source for creating localized excitons, which can dramatically enhance the intensity of photoluminescence. Therefore, interfacial Si-OH bonds are a theoretically convincing possible source of reported interfacial luminescence.

Photochemical conversion of electrically conductive polysilane films into insulators

Electrically conductive polysilane films doped with iodine can be converted into insulators to semiconductors by a photooxidation reaction. The conductivity can be controlled in the range 10−15–10−4 S cm−1 by regulation of the extent of the photooxidation reaction. Since the non-irradiated area of the film keeps its doping susceptibility, it is possible to prepare a conducting pattern on the film by a photolithographic technique. Network polysilanes containing various substituents, prepared by the disproportionation reaction of alkoxydisilanes, were primarily examined, in addition to polysilanes prepared by the Wurtz coupling reaction. UV and IR analyses indicated that the Si-Si bonds in the polysilanes were changed into Si-O-Si bonds and Si-OH bonds by the photooxidation.

Effect of N 2O/SiH 4 ratio on the properties of low-temperature silicon oxide films from remote plasma chemical vapour deposition

Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 °C) from SiH 4N 2O. The effect of a gas-phase reaction on the SiO 2 film properties and Si/SiO 2 interface was investigated. As the partial pressure ratio was increased above N 2O/SiH 4 = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N 2O/SiH 4 <4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (SiOH and SiH) but when N 2O/SiH 4 >4, the incorporation of SiOH bond became significant and Si 1+, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C V and I V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO 2 interface.

29Si MAS NMR study of the structure of calcium silicate hydrate

This paper presents the results of a comprehensive investigation of single-phase calcium silicate hydrate (CSH) with known compositions using the combined capabilities of 29Si magic angle spinning (MAS) NMR, powder X-ray diffraction (XRD), and chemical analysis of the solution and solid. CSH gels with C/S ratios ranging from 0.4 to 1.85 have been synthesized by hydration of highly reactive β-C2S and aqueous reaction of fumed silica with CaO and separately with highly reactive β-C2S. The main findings include the following. (1) CSH shows continuity and diversity in both composition and structure and forms a continuous structural series. (2) Phase-pure CSH has C/S ratios between 0.6–1.54. (3) SiOH and CaOH bonds both occur in CSH, with the abundance of the former decreasing and that of the latter increasing with increasing C/S ratio. Model calculation indicates that there are between 0.13–0.43 SiOH bonds per tetrahedron and the CaOH/Ca ratio varies between nearly 0 and 0.64. An ideal formula for CSH with a C/S ratio of 1.5 is: Ca4.5[Si3O8(OH)](OH)4 · nH2O. A defect-tobermorite structural model is proposed for CSH in which individual layers have the basic structure of 1.4-nm tobermorite but contain a significant concentration of defects and are more disordered. Stacking disorder between adjacent layer and disorder within individual layers may both contribute to the local and long-range disorder and thus to the diversity of CSH.

Tribochemical characterization of the lubrication film at the [formula omitted] interface sliding in aqueous solutions

A chemical characterization of the thin film at the interface between two silicon nitrides sliding in water was performed to analyze the relationship between the tribological properties (sliding with a low coefficient of friction μ = 0.01), the chemical form of lubricating layers and their practical application. The observed low sliding friction, tribo-induced reactions and subsequent film formation are discussed in terms of reactions between silicon nitride and aqueous solutions. Sliding experiments were carried out in pure water, 1% hydrogen peroxide and NaCl solutions, and the worn surface was quantitatively analyzed by EPMA and SEM. In a 1% hydrogen peroxide solution, the coefficient of friction decreased at an earlier stage of the sliding test than in pure water. This result was attributed to an oxidizing agent which accelerated the surface oxidation reaction. But in a 3% sodium chloride solution, the coefficient of friction remained high: μ = 0.8. Analysis of the wear debris of the silicon nitrides in the 3% sodium chloride solution showed that the debris had a composition equal to Na 2O · nSiO 2, indicating that the reaction of Na + with this surfaces suppressed the formation of a lubricating film. We propose that the lubricating surface film is composed of a SiOH bond, which is insoluble in water and is the most probable chemical form.

The chemical etching mechanism of H-terminated Si(111) surfaces in different pH solutions studied by HREELS

The influence of the pH of the last water rinse of hydrogen-terminated Si(111) surfaces has been investigated by high resolution electron energy loss spectroscopy, for pH values of 1 and 5.5. The observed reoxidation of the surface is found to increase with the acidity of the rinsing solution. A mechanism of reoxidation leading to the formation of Si-OH bonds is proposed. This mechanism explains why high-pH buffered HF etching solutions have to be used, in order to produce ideal hydrogen-terminated Si(111) surfaces.

Studies on Reaction Processes of Hydrogen and Oxygen Atoms with H 2O-Adsorbed Si(100) Surfaces by High-Resolution Electron Energy Loss Spectroscopy

Surface reactions of H2O-adsorbed Si(100) with atomic hydrogen and oxygen have been examined by high-resolution electron energy loss spectroscopy (HREELS). The surface with saturated coverage of H2O is terminated by H and OH species and the sticking probability of H2O is estimated to be 0.9. This surface is stable for the adsorption of molecular oxygen at room temperature. The presence of dissociation sites of oxygen molecules such as dangling bonds is considered to be essential to the oxidation of Si(100) surfaces. By the reaction of H2O-adsorbed Si(100) with atomic hydrogen, the uptake of oxygen atoms of Si-OH bonds into sites of Si back bonds occurs even at room temperature.

Structural study of porous silicon

The X-ray absorption near-edge structure of porous silicon with efficient photoluminescence (PL) produced by anodizing Si wafers in an HF-based etch shows the existence of a feature between those assigned to Si-Si and Si-O bonding, which we recently suggested results from the presence of Si-OH. The enhancement of PL intensity was also shown to be dependent on the relative numbers of Si-Si, Si-O and Si-OH bonds. Porous silicon with good visible PL has been produced using (i) photo-assisted etching in HF and (ii)NH 4F:HF-based anodization, and the local structure of these materials is presented. Extended X-ray absorption fine structure (EXAFS) provides evidence for the presence of ~3 ° configurational disorder above the thermal contribution in Si-Si-Si bond angles and for Si-O-Si bridges, i.e. for internal oxygen. In some samples which give strong visible PL, transmission electron microscopy shows that the majority of features on a scale of 5–10 nm have diffraction patterns indicating an amorphous structure. Information on the structure has been obtained as a function of depth from the reflected EXAFS.

Excimer Laser Annealed Poly-Si TFT Technologies

ABSTRACTThis paper describes the excimer laser annealed (ELA) poly-Si TFT technologies in terms of excimer laser annealing of Si films, the leakage current, and the TFT stability. A laser energy density and a shot dependencies of TFT characteristics was analyzed by TEM, SEM, and Raman. The mobility increases with increasing not only the energy density but also the shot density. The mobility increase with the energy density is due to the grain size enlargement. On the other hand, the mobility increase up to 10 to 20 shots is due to a decrease of defects, including small grains, grain boundaries and defects inside grains. The contribution of grain-growth is small. The ELA TFT has a micro-offset structure to reduce the leakage current. Moreover, we have proposed a dynamic leakage current reduction structure. The combination of these technologies provides a sufficiently small leakage current for AMLCDs. The stability of the gate insulator was analyzed. The TFT shows negative threshold voltage shift under gate bias stress. This is due to water penetration and the subsequent field activated chemical reaction in the gate insulator. The dissociation of Si-OH bonds with hydrogen-bonded water was a fundamental contributor. The shift was suppressed sufficiently by hydrogen passivation. Obtained ELA TFTs;s have mobilities of over 100 cm2/Vsec, threshold voltages of less than 3 V, effective leakage currents of less than 10−13 A, and are stable more than 10 years.

Study of HF-Treated Heavily-Doped Si Surface Using Contact Angle Measurements

The surface chemistry of heavily-doped Si treated in a hydrofluoric acid (HF) solution is evaluated using contact angle measurements. The saturated contact angles of H2O on hydrophobic Si surfaces are affected by conduction types and dopant concentrations. Boron-doped surfaces show smaller contact angles, which corresponds to the larger polar-force interaction energy, than phosphorous-doped surfaces. The polar-force interaction is due to the hydrogen bondings between Si–OH bonds, which replace Si–F bonds through hydrolysis reaction in the HF solution, and H2O molecules. In addition, a marked difference in the hydrogen termination process can be observed, depending on the surface orientation, during the dip in extremely dilute HF solution.

Room-temperature water adsorption on the Si(100) surface examined by UPS, XPS, and static SIMS

The adsorption of water on the reconstructed Si(100)-(2 x 1) surface at room temperature is studied using an integrated multi-technique approach. UPS, XPS, and static SIMS surface examination in a variable temperature mode of experimentation indicates dissociative adsorption of water to hydroxyl (OH) and hydride (H) groups saturating the single dangling bonds on adjacent dimer-pair Si atoms of the reconstructed surface. No evidence of molecular water is found. Upon heating the surface the hydroxyl decomposes to bridge-bonded oxygen (Si-O-Si) and additional silicon hydride groups. This is complete at ≈400°C. Above 400°C the surface loses hydrogen, presumably as H 2, and above 600°C the substoichiometric silicon oxide sublimes as SiO to return to the clean, reconstructed surface. The chemical state of oxygen on the surface is monitored as a function of temperature through the use of a Δ parameter (Δ = binding energy O(1s) - binding energy Si(2p)). These results are consistent with experimental evidence and surface chemistry first proposed by others. Assignment of the observed DOS features is made by comparison of the experimental DOS spectra to calculations for the system and for system analogs (SiOH radical, oxygen-saturated Si surface, hydrogen-saturated Si surface), and to another hydroxyl system (NaOH). Four major features of the saturated hydroxyl/hydride surface are found : 5 eV Si-H bond, Sisp 3 + H1s character; 6.4 eV O 2p lone pair, π symmetry nonbonding orbital; 7.6 eV O-H bond, O 2p + H1s character, σ symmetry; 11.9 eV Si-OH bond, sp 3 + O 2p character (binding energies relative to the Fermi level).

Kinetics of enhanced photogeneration of E′ centers in oxygen-deficient silica

The kinetics of the generation of E′ centers induced by a 6.4 eV excimer laser were investigated. Enhanced defect generation was observed in OH-containing oxygen-deficient silicas. The increased E′ centers were found to be correlated with an absorption band at 5.7 eV. The intensity of the 5.7 eV band α, as a function of the laser fluence, F, follows a simple formula of α( F) = α s[1 − exp(− DF)], where the values of α s and the decay coefficient, D, depend on the concentrations of SiH and SiOH bonds.

Study of thermal oxidation and nitrogen annealing of luminescent porous silicon

The properties of thermally oxidized porous Si were studied by Fourier-transform infrared spectroscopy and secondary ion mass spectroscopy. The results show that residual hydrogen exists in the 1000 °C/10 min thermally oxidized porous Si film in the form of SiOH bonds. The removal of these hydrogen atoms by annealing at 1000 °C in N2 reduces the photoluminescence.

Hydrogenating silicon dioxide in an electron cyclotron plasma

The hydrogenating effect of a low-temperature, electron cyclotron resonance excited H2 plasma on the surface chemistry of thermal SiO2 films is analyzed in situ by x-ray photoemission spectroscopy and static secondary ion mass spectrometry. Hydrogenation with this nominal 10 eV proton flux results in Si-(O4), H-Si-(O3), (H2)-Si-(O2), (H2)-Si-O, and H-Si-(Si3) bonding states to the complete exclusion of Si—OH bond formation. A simple thermodynamic argument accounts for the exclusivity of Si—H bonds terminating the outermost (O3)-Si-O-Si-(O3) network of a thick SiOx&amp;lt;2 film, thereby transforming what is normally a hydrophilic surface into one that is hydrophobic.

Positron trap sites in the native oxide film grown on a hydrogen-terminated silicon surface

Positron behavior in thin native oxide layers grown on an initially hydrogen-terminated Si(100) surface was investigated and correlated with the chemical structure of the layers determined using Fourier-transform infrared absorption attenuated total reflection spectroscopy, and x-ray photoelectron spectroscopy. Hydrogen termination of the Si surface by 4 vol % HF treatment gave rise to a narrower Doppler-broadened positron-electron annihilation line than that of bulk Si. By a process of oxidation in pure water very thin (up to 7.8 Å) layers were grown on the H-terminated Si. The Doppler broadening of annihilations from the Si surface was seen to increase monotonically with thickness away from the value seen for amorphous bulk SiO2. The positronium fraction was monitored throughout but was found to be independent of the oxidation duration. It was found that the chemical structure of the surface, in particular the oxidized Si-OH bond, was correlated with the positron annihilation mode and to the level of observed Doppler broadening.

Parasitic Channel Induced by Spin‐On‐Glass in a Double‐Level Metallization Complimentary Metal Oxide Semiconductor Process: Its Formation and Method of Suppression

We studied the degradation mechanism and the suppression method for parasitic channel formation by inorganic spin‐on‐glass (SOG) in complimentary metal oxide semiconductor (CMOS) devices with double‐level metallization using test structures and a high frequency C‐V technique. The positive charge induced near the interface in the field isolation region caused the parasitic channel. We propose a new mechanism that atomic hydrogen created by the SOG film diffuses to the interfacial region and generates the positive charge. There are two distinct mechanisms for the creation of the atomic hydrogen by the SOG films with different cap oxide. In cap which is nondoped silicon oxide deposited by PECVD, Si—OH bonds in the SOG film are broken during the cap deposition and create the atomic hydrogen. In nondoped silicate glass (NSG) cap which is nondoped silicate glass deposited by atmospheric pressure chemical vapor deposition (APCVD), water desorbed from the SOG film reacts with the aluminum electrode and creates the atomic hydrogen. Furthermore, film with higher dangling bond density exhibited a capability to reduce the density of the SOG‐related positive charge. Especially, the bottom film under the SOG film was more effective for reducing the positive charge density compared with the cap film on the SOG film. The improvement is attributed to trapping of SOG‐related atomic hydrogen by the dangling bond in the film. These experimental results are qualitatively explained well with the trapping model introducing the dangling bond as the trap center in the cap and bottom films.

Fluorine Termination of Silicon Surface by F2 and Succeeding Reaction with Water

The F2 treatment of a hydrogen-terminated Si(100) surface in a vacuum chamber was chosen to generate a densely fluorinated silicon surface. It was confirmed by IR-attenuated total reflection and X-ray photoelectron spectroscopy measurements that the Si-H bonds on the surface were replaced with the Si-F bonds and that 1.0 monolayer of the Si-F bonds was formed after 1×104 L exposure. Mass spectrometry measurements of the volatile reaction products indicated that the Si-F bonds were produced by the following reaction: {SiH(surface)+F2(gas)→Si-F(surface)+HF(gas)}. The variation of thus prepared surface in water was also studied. The 1.0 monolayer of Si-F bonds was found to be replaced with the 0.7 monolayer of Si-H bonds and the 0.2-0.3 monolayer of Si-OH bonds after dipping into water for 1 min. The replacement of the Si-F bonds with the Si-H bonds was considered to be the back-bond-breaking reaction by water. Such a reaction between water and the surface Si-F was observed for the first time.