Most physically based modeling software accepts input in the form of geometry definition, physical parameters, initial conditions, and boundary conditions; and then, on the basis of solving physical conservation equations, predicts the steady-state or transient behavior of a system or process. There is a growing need to create software tools that can themselves control or manipulate the physically based models in certain ways to enhance the usability of models for equipment design and process optimization. These required tools can be described broadly in the following categories: sensitivity analysis, parameter estimation, inverse problems, dynamic optimization, and real-time control. This paper discusses generally the development and application of such modeling tools, drawing examples from a specific RTP reactor design. These techniques accelerate significantly the optimal design of processes and the concurrent engineering of real-time process-control algorithms.

The purpose of this article is to present the modeling routes for the chemical vapor deposition process with a special emphasis to mass transport models with near local thermochemical equilibrium imposed in the gas-phase and at the deposition surface. The theoretical problems arising from the linking of the two selected approaches, thermodynamics and mass transport, are shown and a solution procedure is proposed. As an illustration, selected results of thermodynamic and mass transport analysis and of the coupled approach showed that, for the deposition of Si1-x Gex solid solution at 1300 K (system Si-Ge-Cl-H-Ar), the thermodynamic heterogeneous stability of the reactive gases and the thermal diffusion led to the germanium depletion of the deposit.

Experimental measurements of the decomposition of methyltrichlorosilane (MTS), a common silicon carbide precursor, in a high-temperature flow reactor are presented. Methane, hydrogen chloride, and silicon tetrachloride are observed as products of the decomposition. Trapping experiments with acetylene and ethylene also detected SiCl3 as a decomposition product. Upper limits on the concentrations of any CH3Cl, HSiCl3, H2SiCl2, or H2C=SiCl2 which might form are provided. Quantitative measurements of product branching and MTS decomposition rates are presented. The results suggest a radical-chain mechanism for the decomposition in hydrogen but not in helium.

A nonlinear dynamic model of the chemical vapor deposition (CVD) process has been developed and analyzed to obtain insight into the design of an appropriate control structure.

Methyltrichlorosilane (MTS) is a precursor commonly used in the production of silicon carbide for composites, protective coatings, and structural ceramics. Experiments suggest that MTS decomposes in the gas phase to produce a large number of species whose surface reactivity is expected to vary widely. In this work, we discuss the development of a gas-phase mechanism that describes the decomposition of MTS. Rate coefficients for the reactions were obtained from literature sources, theoretical methods, and comparisons with analogous reaction chemistry. Several unknown reaction rates were fit to experimental measurements of MTS decomposition. The results are used to predict the major reaction paths, identify reactions to which product concentrations are sensitive, and determine the rate-limiting step for MTS decomposition.

Niobium oxide films have been prepared by metal-organic chemical vapor deposition (MOCVD) in two different systems via thermal decomposition of Nb(OEt)5.A detailed study by exsitu variable-angle spectroscopic ellipsometry indicates a wavelength dependence of the refractive index that could be described by a Cauchy type dispersion formula and typical values of 1.9 to 2.1 at 632.8nm. The band gap of these films were at about 3.5 and 4eV for the indirect and direct transition. Preliminary results of in-situ ellipsometry at four different wavelengths in the visible and UV will be discusssed. The films were amorphous, extremely smooth and pinhole free and therefore they are useful candidates for interdiffusion barrier layers.

Atmospheric Pressure Chemical Vapor Deposition (APCVD) and powder spray pyrolysis are both pyrolytic thin film deposition techniques that are used to coat glass with thin films at atmospheric pressure. In the present study, the fluid dynamics of each process was investigated by laser light scattering. For each system, a 193 nm ArF excimer laser pulsed at 7 Hz was used for the analysis. In the case of the APCVD reactor, the difference in Rayleigh scattering between helium injected in the reactor and ambient air was used to characterize the process. For the powder spray process, laser scattering off the sprayed powder was used. The effect of various parameters is discussed.

The chemical vapor deposition of silicon nitride can be used to protect advanced materials and composites from high temperature, corrosive, and oxidative environments. Desired coating characteristics, such as uniformity and morphology, cannot be measured in-situ by traditional sensors due to the adverse conditions within the high-temperature reactor. A control strategy has been developed which utilizes a process model and an advanced laser-based sensor to measure the deposition rate of the silicon nitride coating in real-time. The control system is based on a three level hierarchical architecture which functionally separates the process control into PID, supervisory and advanced sensor-based control. Optimal setpoint schedules for the supervisory level are derived from a quasi-fuzzy logic inverse mapping of the process model. An advanced sensor utilizing laser ultrasonics provides real-time coating thickness estimates. Model bias is characterized for each reactor and is correlated on-line with the sensor's deposit thickness estimate. Deviations from model predictions may result in parametric changes to the process model. New setpoint schedules are then created as input to the supervisory control level by regenerating the inverse map of the updated process model.

Suitable feedgas compositions for monophase SiC deposition were determined starting from methyltrichlorosilane-hydrogen-argon mixtures at 1 bar total pressure and H2/MTS ratios between 50 and zero. At temperatures from 900 to 1400°C, only a ratio of 1 at PMTS = 18 mbar gave the desired result. The deposition rate of SiC was determined as a function of MTS and HCl partial pressures, of gas flow rate, and of temperature at a H2/MTS ratio of 1. Two different rate equations were found at [MTS]/[HCI] ≥ 5.8 (region I) and < 5.8 (region II), respectively:

where brackets denote gas concentrations. The apparent activation energy was 380 kJ/mol common to both rate equations. A mathematical model taking into account temperature fields at reactor wall and substrate, heat and mass transport in the flowing gas, and heterogeneous reaction rates jSiC(I) and (II) was developed and found to be in very good agreement with the experimental results.

The fabrication, properties and optics applications of transparent and opaque Chemical Vapor Deposited (CVD) β-SiC are reviewed. CVD-SiC is fabricated by the pyrolysis of methyltrichlorosilane, in excess H2, in a low-pressure CVD reactor. The CVD process has been successfully scaled to produce monolithic SiC parts of diameter up to 1.5 m and thickness 2.5 cm. The characterization of CVD-SiC for important physical, optical, mechanical and thermal properties indicate that it is a superior material for optics applications. CVD-SiC properties are compared with those of the other candidate mirror and window materials. SiC process/property relationships are discussed, emphasizing the differences in process conditions, microstructure, and properties between transparent and opaque CVD-SiC.

Thin films of yttria stabilized zirconia (YSZ) were deposited by metal organic chemical vapor deposition (MOCVD) on cobalt-chromium (Co-Cr) alloys used for orthopaedic implants. TMHD derivatives were preferred for the metalorganic sources over the less expensive fluorinated beta-diketonates as the latter left up to 1% fluorine in the film, as determined by Auger spectroscopy. Crystalline cubic structure of these YSZ films was verified by X-ray diffraction. Columnar grain growth gave a rough surface on thicker YSZ films, which increased wear of the mating polyethylene component during simulation tests. YSZ films under one micron thick were mirror smooth and reduced wear of the polymer component by 70% compared to uncoated Co-Cr. Film adhesion was excellent.

Mullite (3Al2O3.2SiO2) is an ideal candidate for coatings on SiC due to its toughness, corrosion resistance and coefficient of thermal expansion (CTE) match. We have deposited alternating layers of Al2O3 and SiO2 followed by post deposition heat treatment to induce mullite formation at the interface. We found that the devitrification of silica to cristobalite led to spallation of the multilayered coatings due to the fracture within the crystalline silica layers. To understand this transformation better, we studied the effect of pressure and temperature on devitrification of silica in both bulk and in coating form. We have demonstrated that the difference in specific volumes of the two phases plays a key role in the vitreous to crystalline transformation in silica.

Rotating Disk Reactors used for Chemical Vapor Deposition have evolved into a leading manufacturing technology for several materials, including metals, compound semiconductors, oxides, silicides, and nitrides. One of the hurdles to be surmounted in bringing this technology into routine high yield manufacturing has been to produce and maintain a highly uniform temperature distribution over the deposition area. With our recent introduction of the real-time Rotating Wafer Thermal Imaging (RWTI) technique, we have made dramatic improvements in the implementation of multi-zone heating systems and producing a uniform deposition temperature. Using multi-zone heaters we have demonstrated wafer temperature uniformity of less than 2°C in the temperature range from 600°C to 1100°C for 50 mm substrates located on wafer carriers with diameters from 125 to 300 mm. The wafer temperature uniformity dependence upon process parameters such as reactor pressure, reactant flows, and wafer carrier rotation speed was investigated. We have shown that multi-zone heating systems can provide high wafer temperature uniformity over a wide range of the process parameters, whereas single zone heating can provide a high degree of wafer temperature uniformity only for a limited set of process parameters. The experimental data allowed us to establish requirements for the application of single and multi-zone heating systems in vertical MOCVD Rotating Disk Reactors.

SiO2 films were deposited on silicon wafers at 25°C by plasma enhanced decomposition of tetraethoxysilane (TEOS) in a mixture of argon and oxygen. The deposition was performed in a rf-powered (13.56 MIHz) asymmetric plasma reactor. The effect of ion bombardment was evaluated by varying the ion energy flux (IEF) at the substrate surface from 0.93 to 9.94 W/cm2. On-line optical emission spectra (OES) revealed CO, CH, and H peaks whose absorption intensities increased with increasing applied power. On-line mass spectrometer data showed that the peak intensities of OC2H5, SiOH (m/e=45), and HSiOH (m/e=46) fragments decreased with increasing applied power indicating the decomposition of these species. FTIR spectra of the deposited films showed that the concentrations of Si-OH and trapped CO gases in the film decreased with increasing IEF. Also, the FTIR results and the refractive index measurements indicated that the film density increased as a function of IEF. The stoichiometry of the film did not change when IEF was below 2, but for IEF greater than 4.91 W/cm2, the film became Si-rich.

Chemical vapor deposition (CVD) has been used to deposit films such as silicon, silicon oxide, silicon nitride, tungsten, silicide, copper and titanium nitride in the semiconductor industry. The reaction driving forces for CVD are typically temperature for thermal CVD, plasma ionization for plasma enhanced CVD, or atomic oxygen for ozone CVD. In the recent years, plasma enhanced CVD (PECVD) and ozone CVD have found extensive applications in the semiconductor industry, due to the higher deposition rate and lower deposition temperature. For example, PECVD and ozone CVD are used to deposit almost all dielectric films such as silicon oxide and silicon nitride on a wafer. The dielectric films on wafers serve as insulating layers between conducting metal layers and as passivation layer on top of semiconductor devices.

Tungsten and molybdenum hexacarbonyls were used as precursors in chemical vapour deposition process for preparation of W and Mo thin films. Pyrolitical decomposition of these precursors proceeds at temperatures of 250–400°C. Thin films with thicknesses in the range of 0,02–1 μm were deposited on different substrates - bare or covered with CdTe glass, and monocrystalline Si. Microstructural studies performed by Reflection High Energy Electron Diffraction (RHEED) method showed that films deposited tend to grow textured. This is discussed as probably due to differences in the growth rate for various crystal planes. The sheet resistances of the as-deposited W and Mo films are in the range of 20–30 Ω/□ for thicknesses of 0.15 μm. After thermal annealing the resistance of W films drops to about 2 Ω/□ and for Mo films to about 9Ω/□. Decreasing in the resistivity of the films is tightly connected with the decreasing in the impurities concentration. These impurities are considered to be in the base of the observed behaviour of the temperature dependence of the electrical resistance of the films. The CVD-W and Mo films are studied as back contacts on CdTe layer in CdS/CdTe photocells. In the paper some preliminary results are presented for the sheet and contact resistances when CVD W and Mo films are deposited at lower temperatures on the surface of CdTe layers, deposited by closespaced sublimation method. The thin film materials, produced by CVD technology look promising with respect to the required high deposition rates and extremely wide deposition areas in the mass production of solar cells.

In situ microbalance measurements of diamond growth rates are described. These results can be used to test proposed mechanisms for diamond growth and suggest mechanisms for sp2 impurity incorporation. The Thiele modulus is a simple criterion for growth uniformity and is used to compare hot-filament and combustion-assisted growth.

Boron nitride (BN) thin films have been grown on the (100) surfaces of Si, diamond, Ni and Cu via ion beam assisted deposition (IBAD) using electron beam evaporation of B in tandem with N and Ar ion bombardment within the ranges of substrate temperature and ion flux of 200–700°C and 0.20–0.30 mA/Cm2, respectively, Fourier-transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) revealed a growth sequence of amorphous (a-BN), hexagonal (h-BN) and cubic (c-BN) layers on Si and diamond under most conditions. This sequence is attributed primarily to increasing biaxial compressive stress with film thickness due to interstitial Ar incorporation observed via Rutherford backscattering spectroscopy (RBS). The effect of deposition conditions, specifically substrate temperature and bombardment intensity, on the film growth was studied. Increasing the substrate temperature above 400°C led to the onset of the cubic phase at a greater film thickness, while increased ion flux led to earlier growth of this phase. These results may be explained by the relaxation of intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment, respectively. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300°C) is required for nucleation and growth of single phase c-BN by this technique. A combination of h-BN and c-BN was deposited on Ni; only h-BN was obtained on Cu substrates.

A detailed kinetic model of diamond-like film growth from methane diluted in hydrogen using low-pressure, filament-assisted chemical vapor deposition (FACVD) has been developed. The model includes both gas-phase and surface reactions. The surface kinetics include adsorption of CH3· and H·, abstraction reactions by gas-phase radicals, desorption, and two pathways for diamond (sp3) and graphitic carbon (sp2) growth. It is postulated that adsorbed CH2· species are the major film precursors. The proposed kinetic model was incorporated into a transport model describing flow, heat and mass transfer in stagnation flow FACVD reactors. Diamond-like films were deposited on preseeded Si substrates in such a reactor at a pressure of 26 Torr, inlet gas composition ranging from 0.5% to 1.5% methane in hydrogen and substrate temperatures ranging from 600 to 950°C. The best films were obtained at low methane concentrations and substrate temperature of 700°C. The films were characterized using Scanning Electron Microscopy (SEM) and Raman spectroscopy. Observations from our experiments and growth rate data from similar experiments reported in the literature [1] were used to estimate unknown kinetic parameters of surface reactions. The proposed model predicts observed film growth rates, compositions and stable species distributions in the gas phase. It is the first complete model of FACVD that includes gas-phase and surface kinetics coupled with transport phenomena.

A 13.56 MHz inductively coupled plasma(ICP) system has been applied to fabricate diamond and diamond-like carbon from a CH4/H2/Ar plasma. The characterizations of the obtained deposits by transmission electron diffraction, reflection high energy electron diffraction, and Raman scattering revealed that the deposits are diamond crystallites, with crystal sizes ∼1μm, and that they partially include disordered microcrystalline graphite. Although contamination due to etching of the quartz tube exists, this was drastically suppressed by the electrostatic shield(Faraday shield).