Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.     

Chemical vapor deposition of aluminum for ulsi applications

Aluminum has been used widely as a conducting material in the fabrication of integrated circuits, and chemical vapor deposition process for Al has been actively investigated for the application in ultra large scale integration. In this review, various precursors, mainly alkyl aluminum and alane compounds, and reaction mechanisms of these precursors in Al CVI) are described. Epitaxial growth and selectivity of the deposition are also discussed. In addition to thermal reactions, plasma and photochemical reactions are also briefly described.     

Effect of fluorine chemistry in the remote plasma enhanced chemical vapor deposition of silicon films from Si2H6-SiF4-H2

SiF₄ was added into Si₂H₆-H₂ to deposit polycrystalline silicon films at low temperatures around 400°C in a remote plasma enhanced chemical vapor deposition reactor. It was found out that the fluorine chemistry obtained from SiF₄ addition had an influence on the chemical composition, crystallinity, and silicon dangling bond density of the film. The fluorine chemistry reduced the amount of hydrogen and oxygen incorporated into the film and also suppressed the formation of powders in the gas phase, which helped the crystallization at low temperatures. Effect of SiF₄ concentration as well as the deposition temperature was also significant.     

Electrochemical deposition of Pt nanoparticles on CNTs for fuel cell electrode

In order to increase the performance of fuel cell electrode, carbon nanotubes (CNTs) were used as support instead of conventional carbon black, and the Pt catalyst was synthesized by using electrochemical deposition (ECD) method which has recently been adopted as a synthetic tool of metal nanoparticles. CNTs used in this paper were grown directly on carbon paper by chemical vapor deposition (CVD) of acetylene. Highly dispersed and nano-sized Pt particles were electrochemically deposited on CNTs surface, which would simplify the manufacturing process of membrane-electrode-assembly (MEA). Pt particles on CNTs were investigated by SEM and TEM. The particle size of Pt is less than 2 nm, which is relatively small compared to that of conventional wet impregnated catalyst (2–8 nm). CO chemisorption results show that the amounts of catalytic sites are about three times larger in Pt/CNT prepared by ECD than those in conventional wet-impregnated one. The mass activity of the former catalyst for oxygen reduction is more than three times higher compared to that of the latter one. This paper was presented at the 11th Korea-Japan Symposium on Catatysis held at Seoul, Korea, May 21–24, 2007.     

Growth of ZnO nanoneedles on silicon substrate by cyclic feeding chemical vapor deposition: Structural and optical properties

Well-crystallized ZnO nanoneedles were grown on Au-coated Si(100) substrate by cyclic feeding chemical vapor deposition (CFCVD) process using diethyl zinc and oxygen as precursors for zinc and oxygen, respectively. Morphological investigations revealed that the as-grown nanoneedles exhibited sharpened tips and wider bases, having the typical diameters at their bases and tips, 60±10 nm and 20±10 nm, respectively. Detailed structural characterizations confirmed that the as-grown products were single crystalline with a wurtzite hexagonal phase and were grown preferentially along the [0001] direction. The room-temperature photoluminescence (PL) spectrum showed a strong and sharp UV emission at 378 nm with a very weak, suppressed and broad green emission at 520 nm, substantiating good optical properties for the as-grown ZnO nanoneedles.     

Preparation, crystal structure, and photocatalytic activity of TiO2 films by chemical vapor deposition

Photocatalytic activities of TiO₂ films were experimentally studied. TiO₂ films with different crystal structures (amorphous, anatase, rutile) were prepared by a Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD) at different reaction temperatures and also by a Sol-Gel method using TTIP (Titanium Tetra Iso-Pro-poxyde). The Effect of CVD preparation method, CVD reaction conditions, crystal structure and wave-length of UV light on the photocatalytic decomposition rate of methylene blue in aqueous solution were studied. First, the characteristics of CVD preparation of TiO₂ films, such as the CVD film growth rate, crystal structure and morphology of the grown TiO₂ films, were experimentally studied as a function of CVD reaction temperature. Secondly, photocatalytic activities of TiO₂ films were evaluated by using two types of photo-reactors. The results indicated that TiO₂ films prepared by CVD exhibit higher photocatalytic activity than a catalyst prepared by the Sol-Gel method. Among the CVD grown TiO₂ films, anatase and rutile showed high photocatalytic activities. However, amorphous TiO₂ films showed lower activities. The activity of the photocatalysts of anatase films was excellent under all types of UV-lamps. The activity of CVD-prepared anatase films was four to seven times higher than that of photocatalyst films prepared by the Sol-Gel method.     

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.     

Metalorganic chemical vapor deposition of Sr x TiyO z thin films by using mixed metal precursorsO z thin films by using mixed metal precursors

Strontium titanate (Sr _x Ti _y O _z ) thin films were prepared by a chemical vapor deposition method using gaseous compounds, obtained by vaporizing a solid mixture of Sr(dpm)₂ and Ti(O-iPr)₂(dpm)₂ in one step, as the metal sources. The compositions of the films changed in proportion to the ratio of the precursors in the solid mixture, which is contrary to the case of films obtained from a mixture of individual precursor vapors. In the latter case, the film composition was not proportional to the mixing ratio of the precursors. The strontium titanate concentration in the film was changed by the deposition temperature even when the Sr/Ti ratio of the feed was fixed, i.e., the Sr/Ti ratio in the film decreased at high temperatures. An SrTiO₃ film, with an Sr/Ti ratio of 1/1, was obtained at 450 ‡C by using vapors from a solid mixture containing the metal precursors at a Sr/Ti of 1/1. The temperature, 450 ‡C in this case, was lower than that for producing the same film composition by a liquid injection method, 550 ‡C. The decomposition of the Ti and Sr precursors included in the solid mixture and possible reactions between them at elevated temperatures were investigated by thermogravimetry, differential scanning calorimetry, and mass spectrometry. When the solid mixture was heated, the Sr-O bond, that connected Sr to the dpm ligand, was dissociated at temperatures lower than 100 ‡C and the isopropoxide ligand of the Ti precursor was dissociated from the Ti atom at temperatures below 150 ‡C. At 162 ‡C, Ti(O-iPr)₂(dpm)₂ melted, forming an oligomer by reaction with surrounding Ti and Sr precursors. This reaction was confirmed by the presence of a mass peak at m/e=585, corresponding to a hetero-metallic compound containing Sr and Ti. The hetero-metallic compound vaporized at temperatures below 200 ‡C and eventually participated in the formation of a SrTiO₃ film.     

Microstructure and mechanical properties of Si3N4f/BN composites with BN interphase prepared by chemical vapor deposition of borazine

The boron nitride (BN) interphase of silicon nitride (Si₃N₄) fiber-reinforced BN matrix (Si₃N_4f/BN) composites was prepared by chemical vapor deposition (CVD) of liquid borazine, and the microstructure, growth kinetics and crystallinity of the BN coating were examined. The effects of coating thickness on the mechanical strength and fiber/matrix interfacial bonding strength of the composites were then investigated. The CVD BN coating plays a key role in weakening the interfacial bonding condition that improves the mechanical properties of the composites. The layering structure of the BN coating promotes crack propagation within the coating, which leads to a variety of toughening mechanisms including crack deflection, fiber bridging and fiber pull out. Single-fiber push-out experiments were performed to quantify the fiber/matrix bonding strength with different coating thicknesses. The physical bonding strength due to thermal mismatch was discussed.     

A CFD study on a vertical chemical vapor deposition reactor for growing carbon nanofibers

A computational fluid dynamic (CFD) study has been carried out to simulate velocity, temperature, and concentration profiles in a vertical chemical vapor deposition (CVD) reactor used for growing carbon nanofibers (CNFs). CNFs were grown over activated carbon fibers (ACFs) wrapped over an especially designed perforated tube which was vertically mounted in the reactor. The numerical model analysis incorporated the conservation equations of momentum, energy, and species. Natural convection effects on the heat-transfer and the exothermic heat generation due to the decomposition of benzene were included. The model simulation results revealed that approximately uniform temperature and concentration profiles existed in the ACF-packed bed. In addition, multiple combinations of the heating length and the wall temperature of the reactor were possible to achieve the prescribed CVD temperature. Under the simulated CVD conditions, the present model predicted an average carbon deposition rate of 5 × 10⁻¹³ kg/m² s, which corresponded to the yield of ∼0.005 g of CNFs per g of ACFs. The simulation results of this study are important for the optimization of the CVD operating conditions to achieve a high and uniform CNF growth in the vertical reactor.     

Synthesis and properties of macroporous SiC ceramics synthesized by 3D printing and chemical vapor infiltration/deposition

Open porosity cellular SiC-based ceramics have a great potential for energy conversion, e.g. as solar receivers. In spite of their tolerance to damage, structural applications at high temperature remain limited due to high production costs or inappropriate properties. The objective of this work was to investigate an original route for the manufacturing of porous SiC ceramics based on 3D printing and chemical vapor infiltration/deposition (CVI/CVD). After binder jetting 3D-printing, the green α-SiC porous structures were reinforced by CVI/CVD of SiC using CH₃SiCl₃/H₂. The multiscale structure of the SiC porous specimens was carefully examined as well as the elemental and phase content at the microscale. The oxidation and thermal shock resistance of the porous SiC structures and model specimens were also studied, as well as the thermal and mechanical properties. The pure and dense CVI/CVD-SiC coating considerably improves the mechanical strength, oxidation resistance and thermal diffusivity of the material.     

Effects of carbon film roughness on growth of carbon nanotip arrays by plasma-enhanced hot filament chemical vapor deposition

Carbon nanotip arrays were grown from carbon films deposited on silicon substrates by plasma-enhanced hot filament chemical vapor deposition. The carbon films were characterized by the atomic force microscopy and micro-Raman spectrometry and the carbon nanotip arrays were investigated by micro-Raman spectrometry, scanning electron microscopy and X-ray photon spectroscopy. The results indicate that both carbon films and carbon nanotips are made of polyaromatic carbon with turbostratic structure. Carbon films possess various roughnesses, which greatly influence the nanotip growth rate. The theory related to plasma and sputtering effect is used to discuss the results.     

Synthesis and characterization of boron carbide films by plasma-enhanced chemical vapor deposition

The plasma-enhanced chemical vapor deposition of boron carbide was investigated on quartz glass and alumina substrates from a gas mixture of BCl 3 , H 2 , and CH 4 in an inductively coupled plasma (ICP) medium produced by a radio frequency (RF) discharged onto the gases passing through a tubular reactor under atmospheric pressure. A thin solid boron carbide coating with a gray color was deposited on both substrates. The results of XRD revealed that the major solid phase formed in the coating material was β-rhombohedral B 4 C. The SEM analysis showed that the surface homogeneity increased with an increase in the exposure time, and different boron carbide structures were formed at different RF powers and exposure times.     

A study of deposition rate and characterization of bn thin films prepared by cvd

Triethylboron (TEB) and ammonia were employed as precursors in preparation of boron nitride thin films on Si(100) substrate by CVD. Operating parameters such as reactor pressure and feed rates of gases were varied to investigate their effects on deposition rate and film characteristics. Total gas pressure in the reactor was varied from near atmospheric to near 1 torr. Deposition temperature was in the range of 850-1,100‡C. Deposition rate increased with increase of partial pressure of TEB, but decreased with increase of total pressure in the reactor. Deposited films were examined with SEM, FTIR, XPS, AES and XRD. Films were BN of turbostratic structure and their texture and carbon content varied with deposition conditions.     

Aromatization of propane over Zn/HZSM-5 catalysts prepared by chemical vapor deposition

Zinc was introduced into HZSM-5 by chemical vapor deposition (CVD) to investigate the catalytic properties of Zn/HZSM-5 for propane conversion. Irrespective of catalytic precursor or ion exchange method, protons were found to be replaced by Zn ions. However, Zn species in the zeolite were different depending on the precursors used. Although the addition of Zn decreased the intensity of the BrÕnsted acidity, it did not caused the apparent formation of Lewis acid sites unlike Ga/HZSM-5 catalysts. On Zn/HZSM-5, both Zn and protons intervene in propane activation step.     

Influence of purge gas on the characteristics of lead–zirconium–titanate thin films prepared by metalorganic chemical vapor deposition

In order to optimize the metalorganic chemical vapor deposition process for PbZr_xTi_1−xO₃ (PZT) thin films, the effect of purge gas species was investigated. Two steps of gas input process for stabilizing reaction chamber pressure, the gas flow prior to PbTiO₃ (PTO) seed layer deposition and PZT thin film deposition, were varied and their effect on structural and electrical properties were examined with regard to the memory device application. PZT film properties exhibited remarkable dependency on the gas species before PTO seed deposition, and insignificant dependency on the gas species before PZT film deposition. With the optimized pre-deposition gas flow, PZT thin film showed excellent properties such as high (1 1 1)-orientation (92.2%), high remnant polarization value of 71 μC/cm² at 3 V. Retention property also showed a heavy dependency on the pre-deposition gas flow that 91.1% of initial charge could be maintained after 100 h of baking at 150 °C.     

Complex geometry macroporous SiC ceramics obtained by 3D-printing,polymer impregnation and pyrolysis (PIP) and chemical vapor deposition (CVD)

We present here an original route for the manufacturing of SiC ceramics based on 3D printing, polymer impregnation and pyrolysis and chemical vapor deposition (CVD). The green porous elastomer structures were first prepared by fused deposition modeling (FDM) 3D-printing with a composite polyvinyl alcohol/elastomer wire and soaking in water, then impregnated with an allylhydridopolycarbosilane preceramic polymer. After crosslinking and pyrolysis, the polymer-derived ceramics were reinforced by CVD of SiC using CH₃SiCl₃/H₂ as precursor. The multiscale structure of the SiC porous specimens was examined by X-ray tomography and scanning electron microscopy analyses. Their oxidation resistance was also studied. The pure and dense CVD-SiC coating considerably improves the oxidation resistance.     

Morphologies and growth mechanisms of zirconium carbide films by chemical vapor deposition

Zirconium carbide films were grown on graphite slices by chemical vapor deposition using methane, zirconium tetrachloride, and hydrogen as precursors. The growth rate of zirconium carbide films as a function of temperature was investigated. The morphologies of these films at different temperatures were also observed by scanning electron microscopy. The results indicated that the deposition of zirconium carbide was dominated by gas nucleation at temperatures below 1523 K, and by surface process at temperatures higher than 1523 K. By comparison of the deposition activation energies for zirconium carbide and deposited carbon, it was determined that the carbon deposition was the controlled process during the growing of zirconium carbide films. The effect of temperatures on the morphologies of zirconium carbide films was also discussed, based on the carbon deposition process.     

Crystalline structure of YSZ thin films deposited on Si(111) substrate by chemical vapor deposition

Yttria-stabilized zirconia (YSZ) thin films were formed on Si(111) substrate by chemical vapor deposition (CVD) in a temperature range of 650–800 °C using β-diketone metal chelates. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) data evidenced that YSZ thin films have a smooth surface with fine grains and crystalline structure, respectively. The crystalline structure of YSZ films was affected by the deposition temperature. The X-ray photoelectron spectroscopy (XPS) data indicated that the YSZ film grows thick enough to prevent the diffusion of Si.     

Development of a kinetic model for the moderate temperature chemical vapor deposition of SiO2 films from tetraethyl orthosilicate and oxygen

An apparent kinetic model for the chemical vapor deposition of SiO₂ from tetraethyl orthosilicate (TEOS) and O₂ was developed in a poorly investigated range of operating conditions, that is, at atmospheric pressure and between 350 and 500°C, based on literature survey and experimental results obtained in a hot wall tubular reactor. The kinetic model was implemented into the computational fluid dynamics code FLUENT and validated both in shape and value by comparison with experimental deposition rate profiles. It reveals that for the conditions tested, a possible mechanism of SiO ₂ deposition involves two intermediate species formed from TEOS homogeneous decomposition, the first one being active from 300°C and the second one contributing to deposition for temperatures higher than 370°C. The calculated local profiles of gas flow, gas temperature, species mass fraction, and silica deposition rate indicate that the first intermediate species leads to marked film thickness gradients, the second one being more stable as producing uniform thicknesses. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3958–3966, 2018