Chemical vapor deposition thermodynamics

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. 

Lackey, W., Hanigofsky, J., and Freeman, G., Experimental Whisker Growth and Thermodynamic Study of the Hafnium-Carbon System for Chemical Vapor Deposition Applications, 7] Amer. Ceram. Soc., 73(6) 1593-98 (1990)... 

Nickel, K., Riedel, R., and Petzow, G., Thermodynamic and Experimental Study of High-Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition, /. Amer. Ceram. Soc., 72(10) 1804-1810 (1989)... 

Ottosson, M., Harsta, A., and Carlsson, J., Thermodynamic Analysis of Chemical Vapor Deposition of YBa2Cu307 from Different Halide Precursors, Prac. 11th. Int. Conf. on CVD, (K. Spear and G. Cullen, eds ), pp. 180-187, Electrochem. Soc., Pennington, NJ 08534 (1990)... 

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. 

Recently we published a short review of the single source precursor concept in chemical vapor deposition (CVD) and in the sol/gel process [1]. hi this article we described in which way several constituent elements of a targeted material can be assembled in a precursor molecule and how this assembly has an effect on the properties of the hnal material. Three types of precursors have been distinguished (1) Precursors which contain the correct ratio of metallic elements (SSP-I), (2) precursors which besides the correct ratio of metallic elements also have ligands which interact with one another to form only few side-products (SSP-II), and (3) precursors with a surplus of one metallic element compared to a thermodynamically stable phase and which form biphasic mixed-materials on a nanometer scale (SSP-III) [1],... 

Chemical vapor deposition (CVD) of thin solid films from gaseous reactants is reviewed. General process considerations such as film thickness, uniformity, and structure are discussed, along with chemical vapor deposition reactor systems. Fundamental issues related to nucleation, thermodynamics, gas-phase chemistry, and surface chemistry are reviewed. Transport phenomena in low-pressure and atmospheric-pressure chemical vapor deposition systems are described and compared with those in other chemically reacting systems. Finally, modeling approaches to the different types of chemical vapor deposition reactors are outlined and illustrated with examples. 

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

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). 

Noncrystalline solids formation needs to be clarified by reference to the natnre of the final product. Several methods lead to amorphous fine particles, for instance, in solution by controlled precipitation. Through gel formation, poorly crystalline Ti02 can be obtained according to the process Ti(OR)4 -I- H2O Ti(OH)4 gel amorphous Ti02 + H2O. In this case, the compound obtained is thermodynamically stable, as when amorphous films are obtained by chemical vapor deposition, sputtering, flash evaporation, and so on. 

Chemical vapor deposition is a very complex process. There are numerous factors such as type, shape, and size of reactor, gas flow rate and arrangement that can affect the properties of the coating. Therefore, it is necessary to review briefly the process itself which includes reactor, reaction zones, temperature, pressure, precursors, and gas flow dynamics before discussing the thermodynamics and kinetics of the CVD. 

Generally speaking, PEVD is a modified form of chemical vapor deposition (CVD). A comparison between PEVD and conventional CVD is schematically shown in Figure 1 for a product (D) formed from reactants (A) and (B). In a CVD process, both reactants (A) and (B) are supplied through a vapor phase at the same side of a solid substrate (E). They react chemically at the surface of the solid substrate (E), aided by some type of catalytic effect, to form a desired product (D). In a PEVD process, one reactant (A) is transported from one side (source) of a solid substrate (E) to the other side (sink) under well-controlled thermodynamic and kinetic conditions. At the sink side, reaction with (B) occurs to form (D). Further growth of (D) into a continuous thin film with the desired thickness in a PEVD process also relies on (A) transported in the solid state now through (E) and (D) to react with (B). 

The direct reaction between elemental boron and Hj gas has limited utility e.g., MgjBj, which contains elemental boron, does not react with Hj at high T. However the reaction between boron and Hj at 840 C forms only traces of B H, and Hj reacts little with boron powder. Thermodynamic calculations based on free energy minimization for the chemical-vapor deposition of boron from BXj-H mixtures (X = Cl, Br) at 1000-1900 K and 0.101 MPa indicate low borane (BHj) cone at equilibrium, but traces of HBXj are predicted in these T ranges. ... 

Kuta AJ, Davis RF (1983) Thermodynamic calculations for the chemical vapor deposition of silicon nitride. J Am Ceram Soc 66 551-558... 

Nadal M, Grenet T, Teyssandier F (1993) Titanium borides deposited by chemical vapor deposition thermodynamic calculation and experiments. J Phys IV 2 C3-511-518... 

Pierson JF, Belmonte T, Michel H (2001) Thermodynamic and experimental study of low temperature ZrB2 chemical vapor deposition. J de Physique IV, 11, Pr3-85-91... 

Sourdiaucourt P, Derre A, David P, Delhaes P (1997) Thermodynamic study of the hafnium-carbon system for hafnium carbide chemical vapour deposition. In Allendorf MD, Bernard C (eds) Proceedings of the 14th international conference on chemical vapor deposition/Jointly held with the Euro CVD-11. Electrochemical Society, Pennington, NJ, pp31-39... 

Figure D.29 is reprinted from the Electrochemical Society, M Leparoux, Y Boussant and L Vandenbulcke, Thermodynamic analyses of the chemical vapor infiltration in the B-N-Si and B-N-P system, in M D Allendorf and C Bernard eds, Proceedings of the 14th international conference on chemical vapor deposition/jointly held with the EUROCVD-11, pp. 496-503,1997, with permission from the Electrochemical Society.

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