The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

Thermal stability, interfacial structures and electrical properties of amorphous (La₂O₃)_0.5(SiO₂)_0.5 (LSO) films deposited by using pulsed laser deposition (PLD) on Si (1 0 0) and NH₃ nitrided Si (1 0 0) substrates were comparatively investigated. The LSO films keep the amorphous state up to a high annealing temperature of 900 °C. HRTEM observations and XPS analyses showed that the surface nitridation of silicon wafer using NH₃ can result in the formation of the passivation layer, which effectively suppresses the excessive growth of the interfacial layer between LSO film and silicon wafer after high-temperature annealing process. The Pt/LSO/nitrided Si capacitors annealed at high temperature exhibit smaller CET and EOT, a less flatband voltage shift, a negligible hysteresis loop, a smaller equivalent dielectric charge density, and a much lower gate leakage current density as compared with that of the Pt/LSO/Si capacitors without Si surface nitridation.     

Fabrication and characterization of Au/SiO2 nanocomposite films grown by radio-frequency cosputtering

Au/SiO₂ nanocomposite films were prepared on Si wafers by cosputtering of SiO₂ and gold wires. Au/Si atomic ratios in Au/SiO₂ nanocomposite films were varied from 0.53 to 0.92 by controlling the length of gold wire to study the evolution of the crystallization of gold, the size of Au/SiO₂ nanocomposite particles, and the optical properties of as-deposited Au/SiO₂ nanocomposite films. An X-ray photoelectron spectroscopy reveals that Au exists as a metallic phase in the bulk of SiO₂ matrix. Dome-shaped Au/SiO₂ nanocomposite particles and both Au (1 1 1) and (2 0 0) planes were observed in a field-emission scanning electron microscopy and X-ray diffraction studies respectively. With an ultraviolet-visible, absorption peaks of Au/SiO₂ nanocomposite films were observed at 525 nm.     

Electron beam-physical vapor deposition of SiC/SiO2 high emissivity thin film

When heated by high-energy electron beam (EB), SiC can decompose into C and Si vapor. Subsequently, Si vapor reacts with metal oxide thin film on substrate surface and formats dense SiO₂ thin film at high substrate temperature. By means of the two reactions, SiC/SiO₂ composite thin film was prepared on the pre-oxidized 316 stainless steel (SS) substrate by electron beam-physical vapor deposition (EB-PVD) only using β-SiC target at 1000 °C. The thin film was examined by energy dispersive spectroscopy (EDS), grazing incidence X-ray asymmetry diffraction (GIAXD), scanning electron microscopy (SEM), atomic force microscopy (AFM), backscattered electron image (BSE), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and Fourier transformed infra-red (FT-IR) spectroscopy. The analysis results show that the thin film is mainly composed of imperfect nano-crystalline phases of 3C-SiC and SiO₂, especially, SiO₂ phase is nearly amorphous. Moreover, the smooth and dense thin film surface consists of nano-sized particles, and the interface between SiC/SiO₂ composite thin film and SS substrate is perfect. At last, the emissivity of SS substrate is improved by the SiC/SiO₂ composite thin film.     

Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

Structural and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films deposited on LaNiO3 and Pt bottom electrodes

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ thin films were deposited on LaNiO₃(LNO)/SiO₂/Si(1 0 0) and Pt/Ti/SiO₂/Si(1 0 0) substrates by metal-organic decomposition, and the effects of bottom electrodes LNO and Pt on the ferroelectric, dielectric and piezoelectric properties were investigated by ferroelectric tester, impedance analyzer and scanning probe microscopy, respectively. For the thin films deposited on LNO and Pt electrodes, the remnant polarization 2P_r are about 22.6 and 8.8 μC/cm² under 375 kV/cm, the dielectric constants 238 and 579 at 10 kHz, the dielectric losses 0.06 and 0.30 at 10 kHz, the statistic d_33eff values 95 and 81 pm/V. The improved piezoelectric properties could make (Na_1−xK_x)_0.5Bi_0.5TiO₃ thin film as a promising candidate for piezoelectric thin film devices.     

SiO adsorption on a p(2 × 2) reconstructed Si(1 0 0) surface

We have investigated the adsorption mechanism of SiO molecule incident on a clean Si(1 0 0) p(2 × 2) reconstructed surface using density functional theory based methods. Stable adsorption geometries of SiO on Si surface, as well as their corresponding activation and adsorption energies are identified. We found that the SiO molecule is adsorbed on the Si(1 0 0) surface with almost no activation energy. An adsorption configuration where the SiO binds on the channel separating the dimer rows, forming a Si-O-Si bridge on the surface, is the energetically most favourable geometry found. A substantial red-shift in the calculated vibrational frequencies of the adsorbed SiO molecule in the bridging configurations is observed. Comparison of adsorption energies shows that SiO adsorption on a Si(1 0 0) surface is energetically less favourable than the comparable O₂ adsorption. However, the role of SiO in the growth of silicon sub-oxides during reactive magnetron plasma deposition is expected to be significant due to the relatively large amount of SiO molecules incident on the deposition surface and its considerable sticking probability. The stable adsorption geometries found here exhibit structural properties similar to the Si/SiO₂ interface and may be used for studying SiO_x growth.     

Cluster size dependence of SiO2 thin film formation by O2 gas cluster ion beams

Cluster size effects of SiO₂ thin film formation with size-selected O₂ gas cluster ion beams (GCIBs) irradiation on Si surface were studied. The cluster size varied between 500 and 20,000 molecules/cluster. With acceleration voltage of 5 kV, the SiO₂ thickness was close to the native oxide thickness by irradiation of (O₂)_20,000 (0.25 eV/molecule), or (O₂)_10,000 (0.5 eV/molecule). However, it increased suddenly above 1 eV/molecule (5000 molecules/cluster), and increased monotonically up to 10 eV/molecule (500 molecules/cluster). The SiO₂ thickness with 1 and 10 eV/molecule O₂-GCIB were 2.1 and 5.0 nm, respectively. When the acceleration voltage was 30 kV, the SiO₂ thickness has a peak around 10 eV/molecule (3000 molecules/cluster), and it decreased gradually with increasing the energy/molecule. At high energy/molecule, physical sputtering effect became more dominant process than oxide formation. These results suggest that SiO₂ thin film formation can be controlled by energy per molecule.     

Surface chemical states of barium zirconate titanate thin films prepared by chemical solution deposition

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin films grown on Pt/Ti/SiO₂/Si(1 0 0) substrates were prepared by chemical solution deposition. The structural and surface morphology of BZT thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the random oriented BZT thin film grown on Pt/Ti/SiO₂/Si(1 0 0) substrate with a perovskite phase. The SEM surface image showed that the BZT thin film was crack-free. And the average grain size and thickness of the BZT film are 35 and 400 nm, respectively. Furthermore, the chemical states and chemical composition of the films were determined by X-ray photoelectron spectroscopy (XPS) near the surface. The XPS results show that Ba, Ti, and Zr exist mainly in the forms of BZT perovskite structure.     

Electron density profile at the interface of SiO2/Si(0 0 1)

In this report we present grazing incidence X-ray reflectivity (GIXR) study of SiO₂/Si(0 0 1) system. We have analysed the X-ray reflectivity data using recursive formalism based on matrix method and distorted wave Born approximation (DWBA). From the analysis of the reflectivity data we could obtain the electron density profile (EDP) at the interface of the dielectric SiO₂ film and the Si(0 0 1) substrate. The EDP obtained from the matrix method follows the DWBA scheme only when two transition layers are considered at the interface of SiO₂/Si. The layer which is in proximity with the Si substrate has a higher electron density value than the Si and SiO₂ values and it appears as a maximum in the EDP. The layer which is in proximity with the dielectric SiO₂ layer has an electron density value lower than the SiO₂ value and it appears as a minimum in the EDP. When the thickness of the SiO₂ layer is increased the lower density layer diminishes and the higher density layer persists.     

High-temperature oxidation behavior of SiO2 protective layer deposited on IN738LC superalloy by combustion CVD (CCVD)

A SiO₂ protective coating was deposited on an IN738LC alloy using CCVD. The physical properties of a SiO₂ protective layer are influenced by the amount of tetraethyl orthosilicate (TEOS, C₈H₂₀O₄Si). Therefore, the SiO₂ protective coating was deposited using different TEOS concentrations and deposition times to optimize the conditions. The deposited coating layer was confirmed to be a SiO₂ layer by SEM, EDX, and ESCA analyses. The oxidation resistance of the alloy was evaluated by thermo gravimetric analysis. The oxidation resistance of the SiO₂ protective coating was highest when the coating was processed at a TEOS concentration of 0.05 mol/l, which is the highest concentration of source material used. The surface roughness of the SiO₂ protective layer also increased with increasing TEOS concentration. The surface roughness of the coating had little effect on the oxidation resistance for a film thickness of approximately 1 μm.     

Nanostructuring Si surface and Si/SiO2 interface using porous-alumina-on-Si template technology. Electrical characterization of Si/SiO2 interface

In this work, anodic porous alumina thin films with pores in the nanometer range are grown on silicon by electrochemistry and are used as masking material for the nanopatterning of the silicon substrate. The pore diameter and density are controlled by the electrochemical process. Through the pores of the alumina film chemical oxidation of the silicon substrate is performed, leading to the formation of regular arrays of well-separated stoichiometric silicon dioxide nanodots on silicon, with a density following the alumina pores density and a diameter adjustable by adjusting the chemical oxidation time. The alumina film is dissolved chemically after the SiO₂ nanodots growth, revealing the arrays of silicon dioxide dots on silicon. In a next step, the nanodots are also removed, leaving a nanopatterned bare silicon surface with regular arrays of nanopits at the footprint of each nanodot. This silicon surface structuring finds interesting applications in nanoelectronics. One such application is in silicon nanocrystals memories, where the structuring of the oxidized silicon surface leads to the growth of discrete silicon nanocrystals of uniform size. In this work, we examine the electrical quality of the Si/SiO₂ interface of a nanostructured oxidized silicon surface fabricated as above and we find that it is appropriate for electronic applications (an interface trap density below 1–3×10¹⁰ eV⁻¹ cm⁻² is obtained, indicative of the high quality of the thermal silicon oxide).     

Characteristics of silicon oxide thin films prepared by sol electrophoretic deposition method using tetraethylorthosilicate as the precursor

Silicon dioxide films were prepared on p-type Si (1 0 0) substrates by sol electrophoretic deposition (EPD) using tetraethylorthosilicate (TEOS) at low temperature. According to the variation of sol dipping conditions, we estimated the characteristics of SiO₂ films, such as composition, surface morphology, wet etch rate, breakdown voltage, etc. The growth rate of the film increased linearly with increasing TEOS quantity in solution. It increased exponentially with the increase in deposition time, and the film thickness was saturated at approximately 200 nm on hydrophilic Si surface after more than 6 days. The growth rate of the EPD SiO₂ films on the hydrophobic Si surface was much lower than that of the film on the hydrophilic Si surface.     

The simulation study for the nanometer-scale selective growth of Si islands on Si(0 0 1) windows in ultrathin SiO2 films

The nanometer-scale selective growth of Si islands on Si(0 0 1) windows in ultrathin SiO₂ films are studied using the kinetic Monte Carlo simulation. The growth of Si islands is reproduced in simulation where we assume that the migration barrier energy for Si adatom on SiO₂ film is far lower than that on the Si surface at the window.     

Effects of interface between SnO2 thin film and Si substrate on growth time

SnO₂ thin film was grown on Si substrate using the low pressure chemical vapor deposition (LPCVD) method. The SnO₂ thin film was grown in the direction of (110) as deposition time increased. The atomic ratio of O decreased by 62.4, 57.6, and 45.6%, and the thickness of the thin film increased to 0.2, 0.3, and 0.7 ? as the deposition time increased to 10, 20, and 30 min, respectively. The interface of the thin film was examined using high-resolution transmission electron microscope (HRTEM) and energy dispersive spectroscopy (EDS) analysis. The SiO₂ layer was observed at between the SnO₂ thin film and the Si substrate. This layer decreased in thickness as the deposition time increased, which indicates that the deposition time affected the interface of the thin film.     

Novel catalysts: Indium implanted SiO2 thin films

Interactions of Indium (In) and silicon (Si) atoms are known to catalyze certain organic chemical reactions with high efficiency. In an attempt of creating a material that manifests the interactions, In implanted SiO₂ thin films were prepared by ion beam injection and their catalytic abilities for organic chemical reactions were examined. It has been found that, with an injection energy of approximately 0.5 keV, a thin In film is formed on a SiO₂ substrate surface and the In implanted SiO₂ thin film can catalyze an organic chemical reaction. It has been also shown that there is an optimal ion dose for the highest catalytic ability in the film preparation process. Thin-film-type catalyzing materials such as the one proposed here may open a new way to enhance surface chemical reaction rates.     

Pure UV photoluminescence from ZnO thin film by thermal retardation and using an amorphous SiO2 buffer layer

ZnO/SiO₂ thin films were fabricated on Si substrates by E-beam evaporation with thermal retardation. The as-prepared films were annealed for 2 h every 100 °C in the temperature range 400-800 °C under ambient air. The structural and optical properties were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL). The XRD analysis indicated that all ZnO thin films had a highly preferred orientation with the c-axis perpendicular to the substrate. From AFM images (AFM scan size is 1 μm×1 μm), the RMS roughnesses of the films were 3.82, 5.18, 3.65, 3.40 and 13.2 nm, respectively. PL measurements indicated that UV luminescence at only 374 nm was observed for all samples. The optical quality of the ZnO film was increased by thermal retardation and by using an amorphous SiO₂ buffer layer.     

Formation of 10-30 nm SiO2/Si structure with a uniform thickness at ∼120 °C by nitric acid oxidation method

Silicon dioxide (SiO₂) layers with a thickness more than 10 nm can be formed at ∼120 °C by direct Si oxidation with nitric acid (HNO₃). Si is initially immersed in 40 wt.% HNO₃ at the boiling temperature of 108 °C, which forms a ∼1 nm SiO₂ layer, and the immersion is continued after reaching the azeotropic point (i.e., 68 wt.% HNO₃ at 121 °C), resulting in an increase in the SiO₂ thickness. The nitric acid oxidation rates are the same for (1 1 1) and (1 0 0) orientations, and n-type and p-type Si wafers. The oxidation rate is constant at least up to 15 nm SiO₂ thickness (i.e., 1.5 nm/h for single crystalline Si and 3.4 nm/h for polycrystalline Si (poly-Si)), indicating that the interfacial reaction is the rate-determining step. SiO₂ layers with a uniform thickness are formed even on a rough surface of poly-Si thin film.     

Crystallization and surface morphology of Au/SiO2 thin films following furnace and flame annealing

A crystallization and surface evolution study of Au thin film on SiO₂ substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10⁻⁷ mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO₂ substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO₂ system decreases in the range of 350-400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO₂ surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing in the range of 300-310 °C and by flame annealing of a few seconds and up to 0.5 min.     

XPS analysis for degraded Y2SiO5:Ce phosphor thin films

X-ray photoelectron spectroscopy (XPS) results were obtained for standard Y₂SiO₅:Ce phosphor powders as well as undegraded and 144 h electron degraded Y₂SiO₅:Ce pulsed laser deposited (PLD) thin films. The two Ce 3d peaks positioned at 877.9 ± 0.3 and 882.0 ± 0.2 eV are correlated with the two different sites occupied by Ce in the Y₂SiO₅ matrix. Ce replaced the Y in the two different sites with coordination numbers of 9 and 7. The two Ce 3d XPS peaks obtained during the thin film analysis were also correlated with the luminescent mechanism of the broad band emission spectra of the Y₂SiO₅:Ce X₁ phase. These two different sites are responsible for the two main sets of cathodoluminescent (CL) and photoluminescence (PL) peaks situated at wavelengths of 418 and 496 nm. A 144 h electron degradation study on the Y₂SiO₅:Ce thin film yielded an increase in the CL intensity with a second broad emission peak emerging between 600 and 700 nm. XPS analysis showed the presence of SiO₂ on the surface that formed during prolonged electron bombardment. The electron stimulated surface chemical reaction (ESSCR) model is used to explain the formation of this luminescent SiO₂ layer.     

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO₂–SiO₂ thin film was prepared by self-assembly method by mixing SiO₂ precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO₂ and even anatase TiO₂ but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO₂ was incorporated into the film. The self-assembly TiO₂–SiO₂ thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO₂ are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO₂:TiO₂) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.