Modeling of Chemical Vapor Deposition of Large-Area Silicon Carbide

The effects of buoyancy force and substrate rotation on the flow pattern and the ..... force and to improve the film uniformity deposited in a vertica...
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Modeling of Chemical Vapor Deposition of Large-Area Silicon Carbide Thin Film Rong Wang, Ronghui Ma,* and Marc Zupan Department of Mechanical Engineering, UniVersity of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250

CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 11 2592-2597

ReceiVed June 27, 2006; ReVised Manuscript ReceiVed August 14, 2006

ABSTRACT: A two-dimensional mathematical model of transport processes for the deposition of large-area silicon carbide thin film in a cylindrical vertical cold wall reactor is developed by considering transport of mass, momentum, and energy; gas-phase chemistry; and deposition of reacting species on the surface. The model is employed to simulate the polycrystalline 3C-SiC film (100 mm in diameter) deposition process in moderate- and near-atmospheric-pressure regimes, providing knowledge of the flow field, temperature, species concentration, and deposition profile. The effects of buoyancy force and substrate rotation on the flow pattern and the deposition rate are studied in two different reactor configurations: flat top reactor and cone top reactor. It is illustrated that the cone top geometry of the reactor can significantly modify the gas flow pattern and, subsequently, reduce the nonuniformity of the deposition rate. Simulations are performed for a wide range of processing parameters, including the deposition pressure and substrate rotation rate. Understanding of the relationship between processing conditions and the uniformity of the film thickness is achieved. Reactor geometry and processing conditions that favor the deposition of the uniform film are proposed. 1. Introduction Silicon carbide (SiC) has become an attractive material for microelectromechanical systems (MEMs) functioning in harsh environments. Historically known for its excellent mechanical properties such as high stiffness, high hardness, and good wear resistance, SiC also displays good chemical resistance, stability at high temperatures, noticeably wide band gap, high breakdown voltage, and high thermal conductivity compared to silicon.1-4 Silicon carbide is a polymorphic material that exhibits more than 250 different polytypes, which are described using a nomenclature that gives both the crystalline symmetry (C ) cubic, H ) hexagonal) and stacking periodicity. Among the more than 250 different polytypes of silicon carbide, the 3CSiC, 4H-SiC, and 6H-SiC polytypes are believed to be the most relevant to MEMs applications.5,6 The cubic structure is especially advantageous for micromachining because 3C-SiC is the only known polytype that can be heteroepitaxially grown on non-SiC substrates such as Si or SiO2- and Si3N4-coated Si substrates.7-9 The further advancement of SiC technology in MEMs applications demands single crystalline or polycrystalline 3C-SiC to be grown on large-area substrates that are compatible with the economical high-throughput batch-fabrication processes used in the silicon micromachining and integrated circuit industries.7 The challenges in large-area deposition include, but are not limited to, maintaining high growth rate, good surface morphology, and film uniformity. Among a wide variety of techniques for the production of SiC films,10-21 chemical vapor deposition (CVD) has been extensively used for the deposition of both epitaxial and heteroepitaxial thin films.18-20 Specifically, cold wall vertical reactors have demonstrated the ability to deposit 4H- and 6H-SiC epitaxial layers as well as single crystalline or polycrystalline 3C-SiC films on large diameter substrates under low-pressure growth conditions.20,21 The quality of the thin film produced in this type of reactor is profoundly influenced by the complex transport processes and chemical reaction kinetics. The flow pattern, temperature distribution, and C:Si ratio can * Corresponding author. Phone: 410-455-1965. Fax: 410-455-1052. E-mail: [email protected].

strongly affect the deposition rate and film microstructure. Therefore, growth of a large-area polycrystalline 3C-SiC film of uniform thickness, doping concentration, composition, and microstructure demands in-depth understanding of the deposition process as well as optimization of reactor design and processing parameters. Numerical simulation provides a powerful and rapid means for understanding the physics of material processing, examining the effect of control parameters, and optimizing reactor design to achieve desirable film characteristics. Modeling of SiC film growth in hot wall and cold wall reactors has been performed to understand the formation of a Si cluster on the surface and its effect on surface morphology.18,22,23 Deanna et al.24 conducted an experimental and numerical study of poly-3C-SiC film growth on a substrate 100 mm in diameter at atmospheric pressure. In their experimental setup, the substrates were placed vertically in the reactor, allowing two wafers to be processed in one deposition run. The as-deposited films displayed a large variation in thickness between the substrate center and the edge. The numerical study of the gas flow attributed the nonuniformity of the film thickness to the buoyancy flow that caused circulation of the gas mixture at the bottom of the substrate. Dollet et al.18 performed simulations of 3C-SiC deposition in a 70 mm diameter reactor with special attention focused on the gas phase and surface chemistry. A new simplified chemical reaction mechanism was proposed, and deposition profiles obtained using the different reaction mechanisms were compared with the experimental measurements. The present study focuses on the numerical study of poly3C-SiC film deposition on a single horizontally mounted 100 mm diameter substrate in moderate- and near-atmosphericpressure regimes using a cold wall vertical reactor. A comprehensive numerical framework for transport of momentum and energy is developed to predict gas velocity and temperature distribution in the reactor. Chemical reactions in the gas phase and on the substrate surface are incorporated into the transport model for predicting gas species transport and deposition. Numerical simulation is performed examining the effects of design and operating parameters including two reactor configurations, deposition pressure, and substrate rotation rate. This

10.1021/cg060401b CCC: $33.50 © 2006 American Chemical Society Published on Web 09/30/2006

Modeling of CVD of Large-Area Silicon Carbon Thin Film

Crystal Growth & Design, Vol. 6, No. 11, 2006 2593 axisymmetric system, for low-Mach-number laminar flows, the conservation of momentum in vector notation is given as

{

}

2 Fv‚∇v ) -∇p + ∇ µ[∇v + (∇v)T] - µI∇‚v + Fg 3

(2)

Here, p is the pressure, g is the gravitational acceleration, µ is viscosity, and I is the identity tensor. The conservation of energy is

∇‚(Fvh) ) ∇‚(k∇T) + Q

(3)

where h is the enthalpy, k is the thermal conductivity, and Q is the heating source term. The reacting gas species transport in the reactor is governed by the conservation of individual mass Figure 1. Schematics of cold wall CVD reactors studied in this manuscript: (a) flat top reactor and (b) cone top reactor. Table 1. Details of Calculation Parameters for the Flat Top Reactor case

P (Torr)

Q (slm)

Re

Gr

Gr/Re2

1 2 3

100 500 760

27 27 27

17 17 17

2349 58725 135678

7.75 193.96 448.13

paper provides an understanding of the complex mechanism of poly-3C-SiC deposition, leading to improved reactor geometry designs and operational parameters. 2. Computational Model 2.1. Mathematical Model. The fluid flow and heat and mass transfer in the reactor are governed by the conservation of momentum, thermal energy, and individual and total mass. Because of the reactor geometries (Figure 1), the following treatment assumes an axisymmetric steady state during film growth. The Reynolds number evaluated using the deposition conditions (Table 1) shows that the gas flow in the reactor is laminar. The viscous dissipation of the gas mixture is neglected. The gas mixture is treated as an ideal gas and transparent for radiation. The effect of thermal diffusion on gas species’ transport is considered. It should be noted that these assumptions do not decrease the accuracy and limit the application of the model for a wide range of CVD process conditions. The conservation of mass is described by the following equation

∇‚(Fv) ) 0

(1)

where F is the density of the gas mixture and v is the velocity. In an

∇‚(FvYi) ) ∇‚(FD∇‚Yi) + ω˘ i

(4)

where i denotes species i, D is the binary diffusion coefficient of reactants in carrier gases, and Y and ω˘ are the mass fraction and gasphase reaction rate, respectively. The variation of gas mixture density with temperature and pressure is described by the ideal gas law

Yi

∑M

p ) FRT

(5)

i

where Mi is molar mass of the species i and R is the universal gas constant. The viscosity of the carrier gas is calculated using Sutherland’s law. The specific heat and conductivity of the carrier gas are obtained from a database of National Institute of Standards and Technology (NIST).28 Binary diffusion coefficients are calculated by transport theory.29 2.2. Gas-Phase Chemistry and Surface Reaction. Historically, silane (SiH4) and propane (C3H8) highly diluted by a carrier gas hydrogen are used as precursors to expitaxially or heteroexpitaxially deposit SiC films. Various chemical reaction mechanisms have been proposed with different levels of complexity. Allendorf and Kee proposed a model for the reaction mechanism involving 41 species and 119 reactions.25 Danielsson et al. considered the participation of organosilicon species and proposed a rather large mechanism including 35 species and 127 reactions in SiH4/C3H8/H2 mixture.23 However, modeling a large number of participating species and reactions in 2D and 3D simulations can be protracted because of limitations in computing capacity. Considering the fact that most of the species have very low concentration and do not influence Si and C atom transport to the deposition surface, Annen et al.26 proposed a simplified reaction model involving 10 species and 13 reactions. Dollet et al.18 derived

Figure 2. Distributions of stream function (left) and temperature (right) in a flat top reactor for the deposition pressure of 100 Torr.

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Figure 3. Distributions of mass fractions of (left) C2H4 and (right) SiH2 in a flat top reactor for the deposition pressure of 100 Torr. another model, with 18 species and 33 reactions accounting for the organosilicon species. The study concluded that the simulated deposition profile resulting from the reduced model shows good agreement with experimental measurements. In the present study, we employ the simplified gas-phase mechanism proposed by Dollet et al.18 Currently, the processes involved in the surface reactions are difficult to describe because of the highly complicated physical phenomena involved, including but not limited to adsorption, dissociation, island formation, and island desorption. When the surface deposition occurs at a high temperature, beyond 1500 K, the process is considered to be transport limited,27 and a simple approach using the sticking coefficient as proposed by Dollet et al.18 is commonly adopted for calculating the deposition rates. In this approach, the deposition rate at the substrate surface, ω˘ , can be determined from thermodynamics and is given as

ω˘ ) γ

RT [X] x2πM

(6)

where γ is the sticking coefficient of species with molar mass M, and [X] is the molar concentration of gaseous species X. In the current study, the sticking coefficients of all participating species are taken from the work of Dollet et al.18 It is noted that the deposition rates of Si and C atoms calculated using eq 6 are not necessarily the same. To enforce stoichiometry, the smaller of the two deposition rates between Si and C is used, resulting in equal amounts of Si and C being deposited. 2.3. Boundary Conditions. Schematics of the flat top and cone top reactor geometries being studied in the numerical simulations are shown in Figure 1. The flat top growth system consists of a vertically positioned double-walled quartz tube 160 mm in diameter and a substrate situated 150 mm from the gas inlet. The mixture of the precursors and carrier gas is delivered from the top inlet of the chamber and exhausted from the bottom outlet. A 100 mm diameter substrate is mounted on a susceptor made of dense graphite with SiC coating. The susceptor also serves as a resistant heater. Experimentally, the carrier and precursor gas mixture are usually forced through a screen or “showerhead” so that uniform gas velocity, temperature, and gas species concentration are prescribed at the inlet. The gas temperature at the inlet is 323 K. The flow rates of hydrogen, silane, and propane are 27 slm and 1.8 and 2.1 sccm, respectively. The susceptor and the substrate are assumed to be at a uniform temperature of 1550 K, as described in the reference as a typical deposition temperature for poly-3C-SiC thin film growth.24 The reactor wall is considered to be an isothermal surface at 323 K, because the quartz tube is cooled by circulating water for minimizing material deposition on the wall. 2.4. Computational Issues. The commercial software CFD-ACE is employed for solving the coupled partial differential equations and the associated gas/surface chemical reactions using the finite volume method with a second-order differencing scheme for all variables. The stability of the numerical solution of the nonlinear system of equations

Figure 4. Variations of deposition rate in the radial direction in (a) the flat top reactor and (b) the cone top reactor for deposition pressures of 100, 500, and 760 Torr. is achieved by using under-relaxation when necessary. A mesh system used in the modeling is 349 × 133. The grid dependence of the results has been examined by using a refined grid system, 698 × 266. The results produced by the two meshes show less than 2% difference.

3. Results and Discussion 3.1. Polycrystalline 3C-SiC Thin Film Deposition at Moderate Pressure of 100 Torr. The deposition of poly-3CSiC thin film in the flat top reactor as shown in Figure 1a is

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Figure 5. Distributions of (left) stream function and (right) temperature in a flat top reactor for the deposition pressure of 500 Torr.

simulated at a deposition pressure of 100 Torr with stationary substrate. Figure 2 shows the simulated gas flow field and temperature distribution in the flat top reactor. It can be seen that the flow field is dominated by the downward forced flow and that no vortex is generated. The temperature distribution of the gas mixture in the radial direction adjacent to the substrate surface is nearly uniform. In the vicinity of the substrate, the gas-phase chemical reactions occur because of the elevated temperature, creating various gas species that lead to the formation of the film. The adsorption rates of Si and C atoms are determined by the reacting species concentration as well as their sticking coefficients. The mass fraction distributions of two of the most important species leading to film deposition, C2H4 and SiH2, are shown in Figure 3. The calculation reveals that the deposition rate of Si atoms is lower than that of C, and thus Si bearing species are controlling the film growth rate under the current growth conditions. The deposition profile in the radial direction as illustrated in Figure 4a shows a higher deposition rate at the edge. The average deposition rate in the radial direction is about 1.2 µm/h. The deposition nonuniformity, defined as the ratio of maximum difference of the deposition rate to the highest deposition rate, 100(Ghighest - Glowest)/Ghighest (%), is 31.2%. 3.2. Effects of Deposition Pressure. The deposition of poly3C-SiC in cold wall reactors has been carried out in a wide pressure range of 40 Torr18 to atmospheric pressure.24 The presence of a great temperature difference between the substrate and the cold wall of the reactor gives rise to a buoyancy-driven flow. The nonlinear interaction between forced and free convection can result in complex flow phenomena, affecting heat transfer, chemistry, species transport, and ultimately film quality. The ratio of Grashof number to Reynolds number square Gr/ Re2, with the physical interpretation of the ratio of buoyancy forces to inertial forces, is employed to determine the dominant force in the reactor. Table 1 gives the values of Gr/Re2 that were evaluated using the characteristic length of the reactor diameter for depositions at different pressures of 100, 500, and 760 Torr. For depositions at 500 and 760 Torr, the values of Gr/Re2 are much greater than unity, indicating that the flow is buoyancy-dominated. We also performed simulations for these pressures with stationary substrate. Figure 4a reveals the adverse effect of increasing the deposition pressure on the film thickness uniformity. Specifically, at atmospheric pressure, the deposition

rate at the edge of the substrate is greater than that at the center by a factor of 4. This can be explained by the change in the flow pattern induced by the deposition pressure. Because the value of Gr increases with the square of the pressure, increasing the deposition pressure will strengthen the buoyancy effects. Therefore, natural convection prevails in a high-pressure deposition regime, giving rise to a vortex adjacent to the substrate, as shown in Figure 5. The presence of the recirculation eddy prevents the fresh gas mixture from reaching the substrate surface directly, depleting the reacting species in the center area above the substrate. Because the growth is transport-limited, the deposition rate is determined by the concentration of the rate-limiting reactants, which are Si-bearing species for the deposition conditions considered in this work. The nonuniform distribution of Si-bearing species leads to a varying film thickness in the radial direction. 3.3. Effects of Reactor Geometry. Reactors with configurations other than a straight tube have been used for the film deposition. For example, Deanna et al. 199824 used a tube reactor with a cone-shaped top (referred to as cone top reactor in this work) for depositing poly-3C-SiC film. In this paper, we examine the effect of this cone top, as shown in Figure 1b, on the deposition uniformity by simulating the depositions under identical processing conditions, as in sections 3.1 and 3.2. The calculated gas flow fields and temperature distributions in the cone top reactor at deposition pressures of 100, 500, and 760 Torr are presented in Figure 6, and the corresponding deposition profiles in the radial direction are given in Figure 4b. Interestingly, the deposition profiles obtained at various pressures show different trends in the radial direction. For the depositions at moderate- and near-atmospheric-pressure regimes (100 and 500 Torr), the deposition rates decrease in the radial direction from the center to the edge, and the average deposition rates are greater than those produced by the flat top reactor. However, atmospheric growth conditions result in a deposition profile similar to that obtained in the flat top reactor. The variation in the deposition profiles can be attributed to the change of the flow fields caused by the reactor configuration. At moderate operating pressures, the reduced inlet area produces a gas flow of higher velocity from the top inlet to the substrate, given that the carrier gas flow rate is fixed. The strong downward flow counteracts the buoyancy force and mitigates the effect of natural convection. Consequently, the global circulation of the gas

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Figure 6. Distributions of (left) stream function and (right) temperature in a cone top reactor for deposition pressures of (a) 100, (b) 500, and (c) 760 Torr.

mixture is not observed, except for deposition under atmospheric conditions. The strong downward flow at the center of the reactor also facilitates the transport of reacting species to the substrate surface, leading to an elevated deposition rate at the center of the substrate. As the gas mixture flows downward, the expanding flow path at the connection of the cone top and the straight tube generates a localized vortex, as illustrated in Figure 6a, trapping the reactants and leading to a low deposition rate at the edge of the substrate. In the case of deposition at 760 Torr, the buoyancy force is so strong that it creates a global natural convection, with the gas flowing upward in the center of the reactor and downward along the wall. The global recirculation results in a deposition profile similar to that obtained in the flat top reactor at the same deposition pressure. At 100 Torr, the cone top reactor produces a deposition nonuniformity of 16.4%, much lower than that of flat top reactor (31.2%). However, the film deposited at 500 and 760 Torr is still highly nonuniform. It can be concluded that the cone top reactor effectively suppresses the occurrence of buoyancy-driven flow and improves the film uniformity at a pressure of 100 Torr. 3.4. Effects of Substrate Rotation. Rotation of the substrate has been extensively used as an effective means to suppress

the circulation eddy above the substrate caused by buoyancy force and to improve the film uniformity deposited in a vertical CVD reactor. The substrate rotation generates a centrifugal body force that produces a viscous pumping effect at the center of the substrate, facilitating the downward flow and the transport of reacting species to the substrate. Figure 7a shows the deposition profiles in the radial direction at the pressure of 500 Torr with the rotating rates of 0, 500, 650, and 1000 rpm in the flat top reactor, which correspond to rotational Reynolds numbers of 0, 1.35 × 103, 1.77 × 103, and 2.71 × 103, respectively. Note that the rotation significantly enhances the average deposition rates from 1 to 3.2 µm/h. The rotation rate of 500 rpm maintains the monotonic increasing trend of the deposition profile in the radial direction as the stationary case; nevertheless, it reduces the variation of the deposition rate between the center and the edge. Conversely, the rotation rate of 1000 rpm produces a deposition profile decreasing in the radial direction because of the enhanced pumping effect in the center of the substrate. One would expect that further increasing the rotation would not improve the uniformity. The model explored shows that a rotation rate of 650 rpm produces a low deposition nonuniformity of less than 5%. It is clear that there

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adequate rotation rate has to be determined by considering factors including the flow rate and operational pressure. Acknowledgment. The authors acknowledge financial assistance from the Designated Research Initiative Fund at the University of Maryland Baltimore County. References

Figure 7. Variations of the deposition rate in the radial direction at various rotation speeds in the (a) flat top reactor and (b) cone top reactor operated at the pressure of 500 Torr.

exists an optimal rotation rate for a specific deposition process. Figure 7b shows the effects of rotation in the cone top reactor at 500 Torr with rotation rates of 0, 500, and 1000 rpm. The rotation enhances the rate of deposition, especially at the edge of the substrate, and slightly promotes the uniform deposition. 4. Conclusions A systematic computational study has been conducted to study the transport phenomena in vertical cold wall reactors for poly3C-SiC deposition. The flow pattern can be dominated by either forced convection or buoyancy-driven convection because of the presence of a great temperature difference between the substrate and the cold wall. Natural-convection-dominated flow that often occurs under moderate- and high-operational-pressure regimes can cause gas circulation above the substrate and result in nonuniform film thickness. Deposition under low pressure helps to maintain a vortex-free flow environment but suffers a low deposition rate. A cone top reactor allows the increased inlet carrier gas momentum to counteract the buoyancy-induced vortices and thus suppresses the natural convection and benefits the film growth. The cone top reactor has shown the capability to improve film uniformity at a moderate operational pressure (around 100 Torr). The rotation of the substrate that introduces a centrifugal body force can effectively suppress the buoyancy force, leading to improved film uniformity. However, overrotating the substrate can cause a convex deposition profile. An

(1) Zorman, C. A.; Mehregany, M. Proc. IEEE Sens. 2002, 2, pp 11091114. (2) Powell, A. R.; Rowland, L. B. Proc. IEEE 2002, 90 (6), 942-955. (3) Agarwal, A. K.; Augustine, G.; Balakrishna, V.; Brandt, C. D.; Burk, A. A.; Li-Shu, C.; Clarke, R. C.; Esker, P. M.; Hobgood, H. M.; Hopkins, R. H.; Morse, A. W.; Rowland, L. B.; Seshadri, S.; Siergiej, R. R.; Smith, T. J., Jr.; Sriram, S. Int. Electron DeVices Meet. 1996, 225-230. (4) Lijun, T.; Mehregany, M.; Matus, L. G. Tech. Dig. - IEEE SolidState Sens. Actuators Workshop 1992, 198-201. (5) Mehregany, M.; Zorman, C. A.; Rajan, N.; Wu, C. H. Proc. IEEE 1998, 86 (8), 1594-1610. (6) Mehran, M.; Christian, A. Z. Proc. SPIE 2004, 1-7. (7) Zorman, C. A.; Rajgopal, S.; Fu, X. A.; Jezeski, R.; Melzak, J.; Mehregany, M. Electrochem. Solid-State Lett. 2002, 5 (10), G99G101. (8) Fu, X. A.; Jezeski, R.; Zorman, C. A.; Mehregany, M. Appl. Phys. Lett. 2004, 84 (3), 341-343. (9) Yasseen, A. A.; Wu, C. H.; Zorman, C. A.; Mehregany, M. IEEE Electron DeVice Lett. 2000, 21 (4), 164-166. (10) Kaneko, T.; Miyakawa, N.; Sone, H.; Iijima, M. J. Cryst. Growth 1997, 174 (1-4), 658-661. (11) Yagi, K.; Nagasawa, H. J. Cryst. Growth 1997, 174 (1-4), 653657. (12) Gao, Y.; Edgar, J. H.; Chaudhuri, J.; Cheema, S. N.; Sidorov, M. V.; Braski, D. N. J. Cryst. Growth 1998, 191 (3), 439-445. (13) Hurtos, E.; Rodriguez-Viejo, J.; Bassas, J.; Clavaguera-Mora, M. T.; Zekentes, K. Mater. Sci. Eng., B 1999, 61-62, 549-552. (14) Wischmeyer, F.; Wondrak, W.; Leidich, D.; Niemann, E. Mater. Sci. Eng., B 1999, 61-62, 563-566. (15) Kaneko, T.; Miyakawa, N.; Sone, H.; Yamazakia, H. Surf. Coat. Technol. 2001, 142-144, 360-364. (16) Kimoto, T.; Tamura, S.; Chen, Y.; Fujihira, K.; Matsunami, H. Jpn. J. Appl. Phys., Part 2 2001, 40, (4B), L374-L376. (17) Wagner, G.; Schulz, D.; Siche, D. Vapour phase growth of epitaxial silicon carbide layers. Prog. Cryst. Growth Charact. Mater. 2003, 47 (2-3), 139-165. (18) Dollet, A.; de Persis, S.; Pons, M.; Matecki, M. Surf. Coat. Techn. 2004, 177-178, 382-388. (19) Vorob’ev, A. N.; Bogdanov, M. V.; Komissarov, A. E.; Karpov, S. Y.; Bord, O. V.; Lovtsus, A. A.; Makarov, Y. N. Proceedings of the Third European Conference on Silicon Carbide and Related Materials, Kloster Banz, Germany, Sept 3-7, 2000. In Mater. Sci. Forum 2001, 353-356, 107-110. (20) Rupp, R.; Wiedenhofer, A.; Friedrichs, P.; Peters, D.; Schorner, R.; Stephani, D. Silicon Carbide, III-Nitrides and Related Materials, Parts 1 and 2. In Mater. Sci. Forum 1998, 264, 89-96. (21) Rodriguezclemente, R.; Figueras, A.; Garelik, S.; Armas, B.; Combescure, C. J. Cryst. Growth 1992, 125 (3-4), 533-542. (22) Vorob’ev, A. N.; Karpov, S. Y.; Bogdanov, M. V.; Komissarov, A. E.; Bord, O. V.; Zhmakin, A. I.; Makarov, Y. N. Comput. Mater. Sci. 2002, 24 (4), 520-534. (23) Danielsson, O.; Henry, A.; Janzen, E. J. Cryst. Growth 2002, 243 (1), 170-184. (24) Deanna, R. G. J. Chem. Vap. Deposition 1998, 6 (4), 280. (25) Allendorf, M. D.; Kee, R. J. J. Electrochem. Soc. 1991, 138 (3), 841-852. (26) Annen, K. D.; Stinespring, C. D.; Kuczmarski, M. A.; Powell, J. A. J. Vac. Sci. Technol., A 1990, 8 (3), 2970-2975. (27) Lee, Y. L.; Sanchez, J. M. J. Cryst. Growth 1997, 178 (4), 505512. (28) NIST Chemistry WebBook. 2005, NIST Standard Reference Database No. 69. (29) Bird, R. B. Transport Phenomena; Wiley: New York, 2002.

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