Chemical vapor deposition kinetics

C. C. Battaille, D. J. Srolvitz, J. E. Butler. A kinetic Monte Carlo method for the atomic-scale simulation of chemical vapor deposition application to diamond. J App Phys 52 6293, 1997. 

Chemical vapor deposition is a synthesis process in which the chemical constituents react in the vapor phase near or on a heated substrate to form a solid deposit. The CVD technology combines several scientific and engineering disciplines including thermodynamics, plasma physics, kinetics, fluid dynamics, and of course chemistry. In this chapter, the fundamental aspects of these disciplines and their relationship will be examined as they relate to CVD. 

Souletie, P., and Wessels, B. W., Growth Kinetics of ZnO Prepared by Organometallic Chemical Vapor Deposition, J. Mater. 

Kodas, T. T., Baum, T. H., andComita, P. B., Kinetics ofLaser-Induced Chemical Vapor Deposition of Gold, / Appl. Phys., 62(l) 281-286(July 1,1987)... 

England, K. M., and Mazunder, J., Kinetics and Microstructure of Laser Chemical Vapor Deposition of Titanium Nitride, SPIEProc., 2703 552-562 (Feb. 1996)... 

Chemical vapor deposition processes are complex. Chemical thermodynamics, mass transfer, reaction kinetics and crystal growth all play important roles. Equilibrium thermodynamic analysis is the first step in understanding any CVD process. Thermodynamic calculations are useful in predicting limiting deposition rates and condensed phases in the systems which can deposit under the limiting equilibrium state. These calculations are made for CVD of titanium - - and tantalum diborides, but in dynamic CVD systems equilibrium is rarely achieved and kinetic factors often govern the deposition rate behavior. 

Many semibatch reactions involve more than one phase and are thus classified as heterogeneous. Examples are aerobic fermentations, where oxygen is supplied continuously to a liquid substrate, and chemical vapor deposition reactors, where gaseous reactants are supplied continuously to a solid substrate. Typically, the overall reaction rate wiU be limited by the rate of interphase mass transfer. Such systems are treated using the methods of Chapters 10 and 11. Occasionally, the reaction will be kinetically limited so that the transferred component saturates the reaction phase. The system can then be treated as a batch reaction, with the concentration of the transferred component being dictated by its solubility. The early stages of a batch fermentation will behave in this fashion, but will shift to a mass transfer limitation as the cell mass and thus the oxygen demand increase. 

Application of Supercomputers To Model Fluid Itansport and Chemical Kinetics in Chemical Vapor Deposition Reactors... 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

While the decomposition of silacyclobutanes as a source of silenes has continued to be studied in the last two decades, the interest has largely focused on mechanisms and kinetic parameters. However, a few reports are listed in Table I of the presumed formation of silenes having previously unpublished substitution patterns, prepared either thermally or photo-chemically from four-membered ring compounds containing silicon. Two cases of particular interest involve the apparent formation of bis-silenes. Very low-pressure pyrolysis of l,4-bis(l-methyl-l-silacyclobutyl)ben-zene94 apparently formed the bis-silene 1, as shown in Eq. (2), which formed a high-molecular-weight polymer under conditions of chemical vapor deposition. 

Kinetic profiles, fermentation, 11 29 Kinetic pumps, 21 54—56 types of, 21 63-70 Kinetic rates, 14 607 Kinetics. See also Adsorption kinetics batteries, 3 421-423 chemical vapor deposition, 5 810-812 colloids, 7 291-292... 

Due to the fact that industrial composites are made up of combinations of metals, polymers, and ceramics, the kinetic processes involved in the formation, transformation, and degradation of composites are often the same as those of the individual components. Most of the processes we have described to this point have involved condensed phases—liquids or solids—but there are two gas-phase processes, widely utilized for composite formation, that require some individualized attention. Chemical vapor deposition (CVD) and chemical vapor infiltration (CVI) involve the reaction of gas phase species with a solid substrate to form a heterogeneous, solid-phase composite. Because this discussion must necessarily involve some of the concepts of transport phenomena, namely diffusion, you may wish to refresh your memory from your transport course, or refer to the specific topics in Chapter 4 as they come up in the course of this description. 

A review article on the CVD processes used to form SiC and Si3N4 by one of the pioneers in this area, Erich Fitzer [Fitzer, E., and D. Hegen, Chemical vapor deposition of silicon carbide and silicon nitride—Chemistry s contribution to modem silicon ceramics, Angew. Chem. Int. Ed. Engl, 18, 295 (1979)], describes the reaction kinetics of the gas-phase formation of these two technical ceramics in various reactor arrangements (hot wall, cold... 

In Section 3.4.2, we introdnced the concept of chemical vapor infiltration, CVI, in which a chemical vapor deposition process is carried out in a porous preform to create a reinforced matrix material. In that section we also described the relative competition between the kinetic and transport processes in this processing technique. In this section we elaborate npon some of the common materials used in CVI processing, and we briefly describe two related processing techniques sol infiltration and polymer infiltration. 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

M.E. Coltrin, P. Ho, H.K. Moffat, and R.J. Buss. Chemical Kinetics in Chemical Vapor Deposition Growth of Silicon Dioxide from Tetraethoxysilane (TEOS). Thin Solid Films, 365 251-263,2000. 

P. Ho, M.E. Coltrin, and W.G. Breiland. Laser-Induced Fluorescence Measurements and Kinetic Analysis of Si Atom Formation in a Rotating Disk Chemical Vapor Deposition Reactor. J. Phys. Chem., 98(40) 10138—10147,1994. 

Chemical stability, thermodynamics vs. kinetics, 1, 606 Chemical vapor deposition... 

To properly describe chemical vapor deposition, one must develop a system of equations that encompasses all phenomena involved. This includes a proper representation of reactions in the gas phase, a suitable description of the surface kinetics, and the gas dynamics of a reacting gas mixture. Because the full governing equations are extremely complex and difficult to solve, most authors have examined only limited regimes. For example, we can ignore the gas dynamics... 

Despite the kinetic lability of the Ln-X-cr-bonds (even the thermodynamically very stable Ln-OR bond is subject to rapid ligand exchange reactions [49]) organolanthanide compounds are thermally very robust over a wide range of temperature (Fig. 5) [114, 116, 139, 144-151]. Thermal stability is not only favorable in catalytic transformations at elevated temperatures [47], for the support of volatile molecular precursors is of fundamental importance in chemical vapor deposition techniques the sublimation behavior is a criterion of thermal stability and suitability for these processes (Fig. 5). 

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