Chemical Vapor Reaction Research Articles

EXAFS study on poly-Si1−XGeX films prepared by reactive thermal CVD method

Extended X-ray absorption fine structure analyses were carried out on Si1−XGeX films of different thicknesses, prepared by the reactive thermal chemical vapor deposition (CVD) method. From a Rutherford backscattering measurement, the Ge fraction was found to be high near the substrate interface. The Ge coordination ratio, Ge–Ge bond length and Ge–Si bond length decreased with increasing film thickness. The Ge fraction dependences of these parameters were found to be different from the results of previous studies on Si1−XGeX films prepared by molecular beam epitaxy. Our results are considered to be caused by the local structure formation around the Ge atoms during the reactive thermal CVD process.

Near UV photoluminescence of Hg-doped GaN nanowires

Mass Hg-doped GaN nanowires with an average diameter of about 25 nm and lengths up to hundreds of micrometers are fabricated by chemical vapor reaction. The as-synthesized products have a single crystal phase and grow along the 〈0 0 1〉 direction. The growth of Hg-doped GaN nanowires is suggested for quasi vapor–solid mechanism (QVSM). In particular, for as large-scale GaN nanowires like films, a novel strong near ultraviolet PL spectrum appears with a doping Hg where the Hg-doped GaN nanowires are found to be responsible for the different characteristics; the PL mechanism is explained in detail.

Influences of GeF4 on poly-SiGe films prepared by reactive thermal CVD

Polycrystalline silicon–germanium (Poly-SiGe) thin films are prepared by reactive thermal chemical vapor deposition (RTCVD) at substrate temperature of 450°C using Si2H6 and GeF4 as source gases diluted in Helium. The influences of GeF4 on the properties of poly-SiGe films have been investigated by varying the flow rates of GeF4. The results show that GeF4 plays a very important role in poly-SiGe growth. Introduction of a small flow rate of GeF4 can effectively promotes the nuclei formation on the substrate and decreases the incubation time. Ge content increases with GeF4 flow rate and high Ge content results in an increase of the film surface roughness. It is also found that the film conductivity increases and activation energy decreases with the increase of Ge content.

Photoluminescence of Hg‐doped CdS nanowires

AbstractHg‐doped CdS nanowires with an average diameter of ∼10–15 nm and lengths up to hundreds of micrometers are fabricated by chemical vapor reaction. The as‐synthesized products have a single crystal phase and grow along the 〈001〉 direction. The growth of Hg‐doped CdS nanowires is suggested for the quasi‐vapor–solid mechanism (QVSM). In particular, the PL spectra show enhancing emission peaks that strongly shift to long wavelengths (up to 115 nm redshift) with Hg doping where the Hg‐doped CdS nanowires are found to be responsible for the different characteristics; the PL mechanism is explained in detail. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvement in Thermal Stability of Chemical Vapor Deposition CoSi2/Polycrystalline Silicon Using TiN and Amorphous Silicon Interlayers

The effect of TiN and amorphous silicon (a-Si) interlayers on the thermal stability of a blanket CoSi2 polycrystalline silicon (poly-Si) gate electrode structure has been investigated. CoSi2 was formed by reactive chemical vapor deposition (CVD) using a Co(η5-C5H5)(CO)2 precursor at 650°C. The TiN interlayer effectively suppressed the interdiffusion of the Co and Si atoms between CoSi2 and poly-Si, thus the thermal stability of the structure was improved significantly up to 1000°C. The a-Si interlayer also improved the thermal stability of CoSi2, even though such an improvement is not as great as the effect of the TiN interlayer. We found that the interfacial native oxide between CoSi2 and poly-Si had the same effect as the TiN interlayer in suppressing the interdiffusion of Co and Si atoms.

Preparation of Spherical Bi2O3 Powder by Plasma and Precipitation Processes

Spherical Bi2O3 powder prepared by plasma chemical vapor reaction and aqueous chemical precipitation is studied. The superfine spherical Bi2O3 powder with an average diameter of 1 μm is made by plasma process. During the precipitation process, the micrograph of the Bi2O3 powder can be controlled through the reaction temperature, the rate of addition of the precipitation reagent, the reaction time and the amount of the dispersant. Accordingly, spherical Bi2O3 powder with diameters ranging from 2 μm to 3 μm is prepared. The spherical Bi2O3 particles have such advantages as uniform size distribution and excellent dispersing property. ZnO varistors made from the resultant powder exhibit properties of a low discharge voltage ratio, great eligibility coefficient measured by a rectangle wave of 2 ms 800 A and good stability in the above characteristics.

Synthesis of dense polycrystalline GaN of high purity by the chemical vapor reaction process

A process for producing high-purity, dense polycrystalline gallium nitride is proposed. Dense polycrystalline gallium nitride was produced by the reaction of ammonia, gallium metal, and a halide source in a quartz boat containing metallic gallium. The process is called the chemical vapor reaction process. The hard crust-like pieces of polycrystalline GaN obtained are of high purity, can be used as source material for single-crystal growth by the ammonothermal technique, sublimation, sputtering, and pulse laser deposition.

Topography simulations for contact formation involving reactive ion etching, sputtering and chemical vapor deposition

With the shrinking design rule of semiconductor devices, the aspect ratios of contact holes that connect transistor electrodes to wirings have exceeded 10 at a design rule less than 0.15μm. The contact is formed through sequential processes of reactive ion etching (RIE), TiN sputtering, and tungsten chemical vapor deposition (W–CVD). In such a formation process, a contact hole with a large bottom diameter is required to reduce contact resistance. We developed a contact simulation method for optimizing contact formation. This contact simulation involves sequential simulations of RIE, TiN sputtering, and W–CVD processes, which adopt a particle model based on the Monte Carlo method. These topography simulations were calibrated using experimental results, and each simulation was combined in order to calculate these sequential simulations. We calculated the dependences of etching and W–CVD filling profiles on contact hole depth. The simulation profiles of etching and W–CVD filling were in agreement with the experimental results. The sequential simulations showed that W disconnection occurs at over 2.5μm contact depth with a aspect ratio of 19.2 and the contact resistance increases markedly.

Growth of AlN by the Chemical Vapor Reaction Process

AlN was grown by a chemical vapor reaction process with metallic Al and ammonium chloride as source precursors. A detailed parameter study was performed for direct growth on sapphire substrates. Specular films were obtained with optimum ammonium chloride supply for a given temperature. Due to lack of optimization of initial growth conditions, these specular films on sapphire contained polycrystalline inclusions. These inclusions were successfully avoided by regrowing on metalorganic chemical vapor deposition (MOCVD)-grown AlN templates. Inversion domains which existed in the MOCVD templates were eliminated at the interface of regrowth although the density of edge-type dislocations was not reduced, and remained at 9.3×109 cm-2. Growth on grooved sapphire resulted in AlN domains with their c-axis perpendicular to the sidewalls of the grooves. The top free surface which was inclined by about 20° to the basal plane of the sapphire substrate was m-plane. The top portion of this domain showed reduced dislocation density, as low as 8×108 cm-2.

Pulsed reactive chemical vapor deposition in the C-Ti-Si system from H2/TiCl4/SiCl4

A new route was explored to produce Ti3SiC2-based thin coatings on carbonaceous substrates. This method combines low pressure-pulsed chemical vapor deposition (CVD) and reactive CVD, the gaseous phase being a mixture of SiCl4, TiCl4 and H2. It consists in depositing a pyrocarbon film on the substrate, converting C into SiC (or TiCx) and then converting this carbide into Ti3SiC2. Experiments and thermodynamic calculations were performed and compared. The films were investigated by X-ray diffraction and transmission electron microscopy. Several microstructures consisting of various combinations of Ti3SiC2, C, SiC, TiCx and TiSi2 were obtained.

Growth of A1N by the chemical vapor reaction process and its application to lateral overgrowth on patterned sapphire substrates

Growth of A1N on patterned sapphire substrates was studied. Deep grooves were made on sapphire substrates by a laser-induced backside wet etching technique. KrF excimer laser was irradiated at an interface between sapphire and phenolphthalein/ N-methyl-2-pyrrolidone solution, which acts as a super-heating liquid. An etch rate of sapphire was as high as 6 μm/min for laser power of 1.0 J/cm 2. The A1N layer was grown on the patterned sapphire substrate by chemical vapor reaction process at 1190 °C for 1 h. On the inclined sidewall of the etched grooves, A1N grew with its c-axis perpendicular to the sidewall. This produced m-plane surfaces which were inclined around 20° to the basal plane of sapphire. A threading dislocation density of m-plane A1N domains was 8×10 8 cm −2.

Comparative study of the tribological behaviour of superhard nanocomposite coatings nc-TiN/a-Si 3N 4 with TiN

Superhard nanocomposite nc-TiN/a-Si 3N 4 coatings were prepared by reactive magnetron sputtering (RMS) and pulsed dc plasma-induced chemical vapour deposition (PCVD) on stainless steel substrates. The tribological behaviour of these coatings at room and elevated temperature was compared with that of TiN coatings deposited by RMS and PCVD. The results show that the superhard nanocomposite nc-TiN/a-Si 3N 4 coatings have a somewhat higher friction coefficient of 0.55–0.7 at room temperature that decreases to about 0.4–0.5 at 550 °C. However, the friction coefficient of pure TiN coatings is 0.6 at room temperature and increases to 0.7 after a sliding distance of 0.1 km at 550 °C.

Application of the chemical vapor infiltration and reaction (CVI-R) technique for the preparation of highly porous biomorphic SiC ceramics derived from paper

Chemical vapor infiltration and reaction (CVI-R) is used to produce biomorphic high porous SiC ceramics based on biological structures such as paper. The paper fibers are first converted into a biocarbon (C b) template by a carbonization step. In a second step methyltrichlorosilane (MTS) in excess of hydrogen is infiltrated into the C b-template by CVI technique, depositing a Si/SiC layer around each fiber. The reaction (R) between biocarbon and excess silicon to form additional silicon carbide occurs during a subsequent thermal treatment as a third step of the ceramization process. Due to the mild infiltration conditions (850–900 °C) the initial micro- and macrostructure of the carbon preform is retained in the final ceramics. The applied characterization methods after every step of the ceramization process are X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, Thermal Gravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). The bending strength of the resulting porous ceramics is measured by the double ring bending test. It is found that a slight excess of free Si in relation to the amount of carbon from the C b-template must be deposited in the Si/SiC layer to achieve a nearly complete conversion of the C b-templates into SiC ceramic. The weight gain after infiltration has to be at least 400 wt.%. Varying the infiltration conditions such as temperature, MTS concentration and infiltration time, ceramics in a wide range of porosity (55–80%) and mechanical properties (5–40 MPa) can be produced. A thermal treatment temperature of 1400 °C is found to be optimal for the reaction between the deposited Si and the biocarbon.

Paper derived biomorphic porous titanium carbide and titanium oxide ceramics produced by chemical vapor infiltration and reaction (CVI-R)

Chemical vapor infiltration (CVI) is used for producing biomorphic porous TiC ceramics derived from paper. The paper samples are first carbonized in inert atmosphere to yield biocarbon template structures (C b-template). Subsequently, three routes for converting the C b-templates into TiC ceramics are studied. The first route includes CVI with TiCl 4-H 2. The effect of methane as additional carbon source is investigated on the second route (TiCl 4-H 2-CH 4). Finally, a two step CVI process (Route 3), first TiCl 4-H 2 and subsequent TiCl 4-H 2-CH 4, is performed in order to improve both the grade of conversion of the C b-template into TiC and the mechanical properties of the resulting porous TiC ceramics. Furthermore, porous TiO 2 ceramics are produced by high temperature oxidation of the TiC ceramics in air flow.

Structural and electrical characteristics of epitaxial CoSi2 grown on n-Si0.83Ge0.17/n-Si(001) by reactive chemical vapor deposition using a Si capping layer

Epitaxial cobalt disilicide (CoSi 2 ) layers are grown on n-Si 0.83 Ge 0.17 /n-Si(001) using a sacrificial Si capping layer at the growth temperature T s =650 °C by reactive chemical vapor deposition using cyclopentadienyl dicarbonyl cobalt (Co(η 5 -C 5 H 5 )(CO) 2 ). Structural and electrical properties of epi-CoSi 2 /Si 0.83 Ge 0.17 /Si(001) were measured by transmission electron microscopy, X-ray diffraction, Auger electron spectroscopy and sheet resistance measurement as a function of annealing temperature. The combined results showed that the epitaxial CoSi 2 phase by the reaction of Co with the Si capping layer was formed in the as-grown layers. Rapid thermal anneals for the investigation of thermal stability of the as-grown layers showed good thermal stability of the epitaxial CoSi 2 layers with the low sheet resistance value as low as ≅4.4 Ω/cm up to the annealing temperature as high as 850 °C without the formation of other cobalt silicide phases. At T A =900 °C, Co 2 Si and CoSi phases with higher resistivity were formed due to the reaction of remaining Co on the surface with the diffusing Si or Ge from the SiGe layer and as a result the increase in the sheet resistance value to ≅26.6 Ω/cm was observed.

Deposition of high crystallinity poly-Si films on glass substrate and fabrication of high mobility bottom-gate TFT

High crystallinity polycrystalline silicon (poly-Si) thin films have been fabricated directly on a glass substrate at 450 °C by reactive thermal chemical vapor deposition (RTCVD) with Si 2H 6 and F 2. The film crystallinity was improved by setting either the residence time shorter or a gas flow ratio of F 2/Si 2H 6 around 1/15–1/20, where the gas phase reaction was suppressed and the contribution of F 2 to the surface reaction was enhanced. For fabricating high mobility bottom-gate TFTs (thin film transistors), the effect of thermal annealing on the TFT characteristics was investigated. With a poly-Si film with a high crystalline volume fraction over 90%, the n-channel bottom-gate TFT was fabricated on the thermally oxidized Si wafer. The thermally annealed TFTs in hydrogen ambient at 400 °C for 150 min exhibited a high field effect mobility of 54.5 cm 2/Vs and a high on/off current ratio of 10 5.

Deposition of high crystallinity poly-Si films on glass substrate and fabrication of high mobility bottom-gate TFT

High crystallinity polycrystalline silicon (poly-Si) thin films have been fabricated directly on a glass substrate at 450 °C by reactive thermal chemical vapor deposition (RTCVD) with Si2H6 and F2. The film crystallinity was improved by setting either the residence time shorter or a gas flow ratio of F2/Si2H6 around 1/15–1/20, where the gas phase reaction was suppressed and the contribution of F2 to the surface reaction was enhanced. For fabricating high mobility bottom-gate TFTs (thin film transistors), the effect of thermal annealing on the TFT characteristics was investigated. With a poly-Si film with a high crystalline volume fraction over 90%, the n-channel bottom-gate TFT was fabricated on the thermally oxidized Si wafer. The thermally annealed TFTs in hydrogen ambient at 400 °C for 150 min exhibited a high field effect mobility of 54.5 cm2/Vs and a high on/off current ratio of 105.

Thermodynamic Analysis of Mo<sub>2</sub>C Powder Synthesis by Chemical Vapor Reaction Method

Thermodynamic Analysis of Mo<sub>2</sub>C Powder Synthesis by Chemical Vapor Reaction Method

Structural and electrical characteristics of epitaxial CoSi 2 grown on n-Si 0.83Ge 0.17/n-Si(001) by reactive chemical vapor deposition using a Si capping layer

Epitaxial cobalt disilicide (CoSi 2) layers are grown on n-Si 0.83Ge 0.17/n-Si(001) using a sacrificial Si capping layer at the growth temperature T s =650 °C by reactive chemical vapor deposition using cyclopentadienyl dicarbonyl cobalt (Co(η 5-C 5H 5)(CO) 2). Structural and electrical properties of epi-CoSi 2/Si 0.83Ge 0.17/Si(001) were measured by transmission electron microscopy, X-ray diffraction, Auger electron spectroscopy and sheet resistance measurement as a function of annealing temperature. The combined results showed that the epitaxial CoSi 2 phase by the reaction of Co with the Si capping layer was formed in the as-grown layers. Rapid thermal anneals for the investigation of thermal stability of the as-grown layers showed good thermal stability of the epitaxial CoSi 2 layers with the low sheet resistance value as low as ≅4.4 Ω/cm up to the annealing temperature as high as 850 °C without the formation of other cobalt silicide phases. At T A=900 °C, Co 2Si and CoSi phases with higher resistivity were formed due to the reaction of remaining Co on the surface with the diffusing Si or Ge from the SiGe layer and as a result the increase in the sheet resistance value to ≅26.6 Ω/cm was observed.

Diamond-like carbon microoptics elements

Micro-optic elements were fabricated by reactive sputter deposition or high density plasma chemical vapour deposition of diamond-like carbon films upon a micromachined silicon mould. The main advantages of the deposited films were: their low temperature deposition processes, their chemical inertness, their low internal stresses and the spectral range of light transmittance. Sputter deposited films always showed good step coverage and very smooth surfaces. The chemical vapour deposited films deposited on smooth silicon surfaces were also of good quality, but when deposited upon slightly rough silicon surfaces, they resulted in even rougher films, with relatively bad step coverage.