Grown Silicon Dioxide Research Articles

Electrical characterization of amorphous silicon carbide thin films deposited via polymeric source chemical vapor deposition

Polymeric source chemical vapor deposition (PS-CVD) was used to synthesize amorphous silicon carbide (a-SiC) thin films. The PS-CVD process was conducted at temperatures between 750 and 1000 °C. The substrates used were silicon single crystal wafers of p-type and n-type, and thermally grown silicon dioxide substrates. The chemical and electrical properties of the films were studied by various techniques, including Fourier transform infrared spectroscopy, elastic recoil detection (ERD), and capacitance–voltage technique. A correlation was observed between the average concentration of oxygen in the films and the deposition temperature, linking a low oxygen concentration to a high deposition temperature. However, the concentration of oxygen in the films deposited at the same temperature is independent of the substrate. The thin films deposited at low temperature showed insulating behaviour, while the semiconducting behaviour is obtained at high deposition temperatures. Ohmic contacts were obtained on the deposited semiconductor thin film by evaporating nickel contacts, followed by annealing of the sample at 800 °C for 2 min.

Fabrication and electrical characteristics of organic thin film transistor using π-conjugated dendrimer

We fabricated organic thin film transistors (OTFTs) by using soluble π-conjugated dendrimers of 4(HPBT)-benzene, 4(HPTT)-benzene, and 4(HPDTT)-benzene. Electrical characteristics such as current–voltage characteristic curves and their temperature dependence were measured for the dendrimer-based OTFT devices. The active layer using planar π-conjugated dendrimers was spin-coated, and thermally grown silicon dioxide layer was used as a dielectric layer. Through the measurements of source–drain currents with varying gate voltages, we obtained charge carrier mobility (μ), on/off current ratio (Ion/off), and threshold voltage (Vth). The 4(HPBT)-benzene and 4(HPTT)-benzene-based OTFT devices showed that the μ's were ∼6.2×10−3cm2/Vs and ∼1.9×10−3cm2/Vs, respectively. We measured temperature-dependent mobility and activation energy (Ea) of the dendrimer-based OTFTs by using Arrhenius fitting. The Ea's of 4(HPTT)-benzene and 4(HPDTT)-benzene-based OTFTs were estimated to be ∼0.39eV and ∼0.13eV, respectively. In case of 4(HPBT)-benzene-based OTFT, two trap levels were measured and the Ea's were estimated to be ∼0.027eV and ∼0.22eV.

Photocurrent gain in 4H-SiC interdigit Schottky UV detectors with a thermally grown oxide layer

A large photocurrent increase in 4H-SiC interdigit Schottky UV detectors was observed in the presence of a thermally grown silicon oxide layer. In particular, internal quantum efficiency higher than unity indicated the presence of an internal gain strictly correlated with the presence of the superficial oxide on SiC. Moreover, a long recovery time, in the range of 10–19s, was evaluated by fall-time photocurrent measurements due to the detrapping of charges in the oxide after the irradiation switching off. The photoresponse of the device was analytically described considering the lowering of the surface potential barrier due to charges trapped at the oxide/semiconductor interface.

Double thermal oxidation scheme for the fabrication ofSiO2 nanochannels

We present a planar fabrication scheme for fluidic systems with silicon dioxide nanochannels and assessthe waferscale quality and homogeneity of the fabricated devices. The nanochannels have heightsh ranging from 14 to300 nm and widths w of 2.5, 5 and 10 µm. Compared to other state-of-the-art fabrication techniques, our double thermal oxidationscheme (DTOS) displays improvements with respect to 4 inch waferscale height variationσh≤1.1 nm and lowsurface roughness Ra≤0.5 nm. Our technique is based on well-controlled growth of silicon dioxide, UV lithography,etching, with an etch-stop layer, and glass to silicon dioxide fusion bonding. Thesmallest achievable channel height is controlled by the precision of oxide growth.The fusion bonding protocol is capable of producing very high aspect ratios,w/h>2500. We test the devices by measuring capillary filling speed in different channel heights,ranging from 14 to 310 nm. These tests reproduce as well as extend the results reported byTas et al (2004 Appl. Phys. Lett. 85 3274). A systematic deviation from bulk behaviour hasbeen observed for channel heights below 100 nm.

Brewster-angle analysis of native and photoelectrochemically grown silicon oxide nanotopographies

Brewster-angle reflectometry (BAR) is employed in-situ for the first time for investigation of the silicon oxide/silicon system during photocurrent oscillations in fluorine containing solution. Combining ex-situ Brewster-angle analysis (BAA) and atomic force microscopy (AFM) shows oxide thickness variations between 4.8 and 13.8 nm. The anodic oxide etch rate amounts to 0.1 nm s −1 in contrast to 0.01 nm s −1 for native oxide. The ambient/anodic oxide interface roughness, σ, is 2 ± 0.2 nm while σ for the oxide/silicon interface varies between 1.0 and 1.9 nm. The photocurrent onset, preceding regular current oscillations, is accompanied by roughness changes at the silicon oxide/silicon interface. A quantitative analysis of the overall system by discerning roughness and surface layer contributions is presented.

Wavelength dependence on the formation of SiO2 films by ultraviolet-laser-induced photochemical deposition using silicone rubber

We have proposed a novel method which permits to grow silicon dioxide (SiO2) films on various substrates at room temperature using silicone rubber. In the method, two F2 laser (157 nm) beams are used. One is used for generation of source gases from the silicone rubber (1st laser). Another is used for illumination of a substrate to deposit the films (2nd laser). We study on characteristics of the deposited films using laser beams which have longer wavelengths than the F2 laser beam. When a fourth harmonics of Nd:YAG laser (266 nm) is used as the 1st laser, SiO2 films with no carbon contaminants are grown as same as the case that an F2 laser is used. The films are consisted of granular structures and the grain size become small as the laser fluence of 2nd laser beam increase. When an ArF laser (193 nm) is used as the 2nd laser, the deposition rate of the films is very low and the films have carbon contaminants. It shows that the 2nd laser beam plays an important role not only in the growth of the films but also in the prevention of carbon contaminants being mixed into the film.

Thermally induced stress hysteresis and co-efficient of thermal expansion changes in nanoporous SiO2

The thermomechanical response of electron beam deposited nanoporous silicon dioxide is examined using substrate curvature measurements and nanoindentation. Analysis of the thin film bond angle strain distributions versus temperature indicates that low temperature (T < 100 °C) stress hysteresis and tensioning are primarily attributed to hydrogen bonded water desorption. However, at higher temperatures, the absence of water desorption suggests that the thermomechanical behaviour is related to thermally induced bond angle strain redistributions towards the local bonding environment of quartz and thermally grown silicon dioxide. This is supported by the co-efficient of thermal expansion data that trend lower with higher annealing temperatures. The re-absorption of water into the thin film accounts for the reproducibility of the open-loop stress hysteresis and tensioning observations.

Site‐selective studies of erbium ion defects in thermally grown silicon oxides

AbstractUsing the site‐selective technique of combined excitation emission spectroscopy (CEES), we have studied a variety of Er‐doped silicon oxide layers and silicon‐rich oxide (SRO) layers which contain silicon nanocrystals. With this technique we identi.ed Er cluster defect sites which are created during thermal annealing and which dominate at high Er concentrations. We investigate the role that Si nanocrystals play in the relative abundance of these cluster sites. In attempts to reduce this clustering effect, we observed mixed results by modifying the growth procedure such that Er is already present in the silicon during oxide growth. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Nanocavity Generation in SiO[sub 2] by Kr and Xe Ion Implantation

Implantation of heavy inert gas ions such as Kr and Xe are found to form nanometer-size bubbles/cavities in thermally grown silicon dioxide. Implantation energies were chosen to produce the same projected range R p ∼ 125 nm for the two ions. The bubble/cavity distribution and size are found to be ion-mass-dependent. After thermal annealing the SiO 2 layer implanted with Kr is bubble free while thermal growth of bubbles/cavities is observed for the sample implanted with Xe. These bubbles/cavities created in SiO 2 are reflected by significant reduction in its dielectric constant, thus offering the prospect for an original way of generating low-k materials.

Thermally Induced Atomic Transport in Nanometric LaAlON Films on Si

The thermal stability of nanometric lanthanum aluminum oxynitride films on silicon was investigated in vacuum and oxygen. Isotopic enrichment of the films with 15 N and of the annealing atmosphere with 18 O combined with nuclear reaction analysis and Rutherford backscattering spectrometry provides direct evidence of atomic transport starting at 600°C. Oxygen exchange and nitrogen replacement are identified. Interfacial silicon oxide growth takes place as the interfacial N concentration falls below 5 X 10 21 cm -3 . Complementary X-ray photoelectron spectroscopy shows changes in chemical bonding as a function of annealing temperature and ambient.

Low Temperature High Quality Growth of Silicon-Dioxide Using Oxygenation of Hydrogenation-Assisted Nano-Structured Silicon Thin Films

AbstractWe report a low temperature high quality oxide growth of nano-structured silicon thin films on silicon substrates obtained through a hydrogenation-assisted PECVD technique followed by a plasma enhanced oxidation process. The deposited layers were investigated and compared with respect to their electrical, optical and stoichiometrical properties by means of Ellipsometry, Rutherford backscattering (RBS), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and by current voltage and capacitance voltage measurements on metal-oxide-semiconductor (MOS) structures.

Label-free kinetic study of biomolecular interactions by white light reflectance spectroscopy

Binding of biomolecules in real-time is studied by white light reflectance spectroscopy (WLRS). The experimental apparatus consists of a WLRS setup and a microfluidic channel for the supply of the biomolecules solutions placed above the sample on which the biomolecular interactions take place. Using this setup, it is possible to monitor in real-time the biomolecular film thickness changes during the binding of biomolecules on a properly treated surface. The sample is a silicon wafer with a thick thermally grown silicon dioxide (~1044 nm) and a thin (~35 nm) polymer layer. The proposed methodology has been applied for the monitoring of streptavidin binding to surface-immobilised biotinylated protein. The biomolecular interactions are monitored as shifts of the wavelength where constructive interference is observed. The proposed methodology provides a simple, fast, low cost approach for a label-free monitoring of biomolecular interactions

Structural and nuclear characterizations of defects created by noble gas implantation in silicon oxide

Thermally grown silicon oxide layer was implanted at room temperature with 300keV Xe at fluences ranging from 0.5 to 5×1016Xe/cm2. Bubbles created after Xe-implantation provided a low-k silicon oxide that has potential use as a dielectric material for interconnects in Si integrated circuits. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterization of defects (bubbles, vacancy, gas atoms and other types of defects) created by Xe implantation in SiO2 layer. These measurements suggest that the bubbles observed with TEM for all fluences were a consequence of the interaction between Xe and vacancies (V), with VnXem complexes created in the zone where V and Xe profiles overlap. Negatively charged defects such as (Si–O−, Si–O–O− and O2-) are also created after implantation.

A study of the effect of different catalysts for the efficient CVD growth of carbon nanotubes on silicon substrates

We report on the identification of efficient combinations of catalyst, carbon feedstock, and temperature for the ethanol chemical vapour deposition (CVD) growth of single-wall carbon nanotubes (SWCNTs) onto silicon substrates. Different catalyst preparations, based on organometallic salts (Co, Fe, Mo, Ni acetate, and bimetallic mixtures), have been spin coated onto thermally grown silicon dioxide on silicon chips to perform tests in a temperature range between 500 and 900 °C. The samples have been then characterized by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. Assuming the growth of high-quality isolated nanotubes as target, the ratio in Raman spectra between the intensity of the G peak and of the D peak has been used as the main parameter to evaluate the performance of the catalytic process. A comparison made for both single metals and bimetallic mixtures points out best conditions to achieve efficient CVD growth of SWCNTs.

Pressure effect of growing with electron beam‐induced deposition with tungsten hexafluoride and tetraethylorthosilicate precursor

Electron beam-induced deposition (EBID) provides a simple way to fabricate submicron- or nanometer-scale structures from various elements in a scanning electron microscope (SEM). The growth rate and shape of the deposits are influenced by many factors. We have studied the growth rate and morphology of EBID-deposited nanostructures as a function of the tungsten hexafluoride (WF6) and tetraethylorthosilicate (TEOS) precursor gas pressure and growth time, and we have used Monte Carlo simulations to model the growth of tungsten and silicon oxide to elucidate the mechanisms involved in the EBID growth. The lateral radius of the deposit decreases with increasing pressure because of the enhanced vertical growth rate which limits competing lateral broadening produced by secondary and forward-scattered electrons. The morphology difference between the conical SiO(x) and the cylindrical W nanopillars is related to the difference in interaction volume between the two materials. A key parameter is the residence time of the precursor gas molecules. This is an exponential function of the surface temperature; it changes during nanopillar growth and is a function of the nanopillar material and the beam conditions.

High-Resolution Soft X-ray Photoelectron Spectroscopic Studies and Scanning Auger Microscopy Studies of the Air Oxidation of Alkylated Silicon(111) Surfaces

High-resolution soft X-ray photoelectron spectroscopy was used to investigate the oxidation of alkylated silicon(111) surfaces under ambient conditions. Silicon(111) surfaces were functionalized through a two-step route involving radical chlorination of the H-terminated surface followed by alkylation with alkylmagnesium halide reagents. After 24 h in air, surface species representing Si(+), Si(2+), Si(3+), and Si(4+) were detected on the Cl-terminated surface, with the highest oxidation state (Si(4+)) oxide signal appearing at +3.79 eV higher in energy than the bulk Si 2p(3/2) peak. The growth of silicon oxide was accompanied by a reduction in the surface-bound Cl signal. After 48 h of exposure to air, the Cl-terminated Si(111) surface exhibited 3.63 equivalent monoleyers (ML) of silicon oxides. In contrast, after exposure to air for 48 h, CH(3)-, C(2)H(5)-, or C(6)H(5)CH(2)-terminated Si surfaces displayed <0.4 ML of surface oxide, and in most cases only displayed approximately 0.20 ML of oxide. This oxide was principally composed of Si(+) and Si(3+) species with peaks centered at +0.8 and +3.2 eV above the bulk Si 2p(3/2) peak, respectively. The silicon 2p SXPS peaks that have previously been assigned to surface Si-C bonds did not change significantly, either in binding energy or in relative intensity, during such air exposure. Use of a high miscut-angle surface (7 degrees vs < or =0.5 degrees off of the (111) surface orientation) yielded no increase in the rate of oxidation nor change in binding energy of the resultant oxide that formed on the alkylated Si surfaces. Scanning Auger microscopy indicated that the alkylated surfaces formed oxide in isolated, inhomogeneous patches on the surface.

CVD synthesis of single wall carbon nanotubes devoted to ULSI electronic applications

AbstractWe report a comparison of the behaviour of different catalysts for the ethanol‐CVD growth of single‐wall carbon nanotubes (SWCNTs) on thermally grown silicon dioxide on silicon substrate. The samples have been prepared by spin‐coating organometallic salt (Co, Fe, Mo, Ni acetate, and their bimetallic mixtures) water solutions (ethanol solution for Mo). As grown samples have been characterized by Raman spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. Assuming as target the growth of high quality isolated nanotubes, the ratio in Raman spectra between the intensity of the G peak and of the D peak, has been used as main parameter to evaluate the performance of the catalytic process. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evolution of Structural and Electrical Properties of Plasma Nitrided Silicon Oxynitrides During the Formation Process

In this work the formation of silicon oxynitrides by decoupled plasma nitridation of thin RTO grown silicon oxide films, varying in thickness, and composition was investigated. Non- destructive Cocos measurement techniques were used after each processing step as base oxidation, plasma nitridation and different post nitridation anneals. It was found, that the base oxide thickness strongly influences the interaction of the plasma species with the solid state material, and thereby impacts severely the film properties. A effective model describing the effect of plasma nitridation process on the dielectric material is proposed.

Thermally induced structural changes in nanoporous silicon dioxide from x-ray photoelectron spectroscopy

Morphological changes due to adsorbed gases in nanoporous silicon dioxide thin films are demonstrated using in situ x-ray photoelectron spectroscopy at temperatures in the range 20⩽T⩽300°C. Adsorbed hydrogen bonded water vapor is observed to relax the surface bond strain of low-temperature electron-beam deposited silicon dioxide up to 100°C. This was determined by measuring the width of the Si 2p and O 1s photoemission peak full widths at half maximum, which are distinctly smaller for films with adsorbed water vapor than for the same films after vapor has been outgassed by heating above 100°C. In situ heating in the range 100&amp;lt;T&amp;lt;200°C decreases the peak width as the atoms gain sufficient energy to establish a more homogeneous local bonding environment. This process is overshadowed above 200°C as thermally induced localized bond strains and charge inhomogeneities at the surface begin to introduce disorder, as demonstrated in the repeatable increase in peak spread with temperature for thermally grown silicon dioxide and quartz. The in vacuo peak width behavior in subsequent thermal cycles is repeatable for the nanoporous thin films. However, if the films are reexposed to atmosphere, the initial increase in peak width is seen again.

Oxidation of Si during the growth ofSiOxby ion-beam sputter deposition:In situx-ray photoelectron spectroscopy as a function of oxygen partial pressure and deposition temperature

Oxidation of silicon during the growth of silicon oxide by ion beam sputter deposition was studied by in situ x-ray photoelectron spectroscopy as a function of oxygen partial pressure at various deposition temperatures below $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. At low temperatures, the variation of incorporated oxygen content is similar to a dissociative adsorption isotherm of ${\mathrm{O}}_{2}$ on Si indicating that the surface-confined reaction of the deposited Si atoms with the adsorbed oxygen atoms is the main process. However, it shows a three-step variation with the oxygen partial pressure at high temperatures. The evolution of $\mathrm{SiO}$ species confirmed by the XPS indicates that an adsorption-induced surface reaction and a diffusion-induced internal reaction are the main pathways for the Si oxidation.