Keywords: finite-volume method, evolutionary algorithm, computational fluid dynamics, shape optimization, chemical process, metal-organic chemical vapor deposition.

Metal-organic chemical vapor deposition (MOCVD) is widely employed to achieve high-quality coatings of various semi-conducting materials. In these processes coatings are deposited from gaseous precursors through chemical reactions under the influence of mass, momentum and energy transport. The quality of the coatings is usually determined by the reaction-transport interactions, which depend on reactor design and process parameters. Although MOCVD is essentially a chemical process, the key issue in designing reactors is to optimize their hydrodynamic and thermal behaviour in such a way, that the growth processes take place selectively on the substrate with a high spatial uniformity.

Aiming at a high degree of uniformity of the growth rate across the substrate, MOCVD reactors are commonly equipped with showerhead gas delivery systems [1]. In these cases, the interplay of chemical reactions and transport phenomena can be controlled through the degree of precursor mixing, as determined by the design of the gas delivery system and, particularly the shape of the showerhead. Consequently, a shape-optimization problem arises in connection with the growth uniformity over the substrate [2].

This work provides the computational framework for the shape optimization of a MOCVD system for the growth of aluminum coatings. The framework was based on the integrated use of a computational fluid dynamics (CFD) code and an evolutionary algorithm (EA). In particular, a CFD model developed previously using a commercial CFD code was used to solve the gas flow, heat and mass transfer, and obtain the growth rate profile across the substrate [3]. The MOCVD system, including the shower plate of the gas delivery system, was parameterized and the optimization problem was formulated under the objective of minimizing the non-uniformity of the growth rate across the substrate. The optimization process was based on a multilevel EA [4]. The results showed that the EA was used successfully in the design of the shower plate. Optimal solutions are proposed and compared to the actual design. It was found that the growth rate non-uniformity can be reduced to 1.152% and 4.277% over the substrates in diameters of 40mm and 58mm, respectively.

1

T.C. Xenidou, A.G. Boudouvis, N.C. Markatos, D. Samélor, F. Senocq, N. PrudHomme, C. Vahlas, "An experimental and computational analysis of a MOCVD process for the growth of Al films using DMEAA", Surface and Coatings Technology, 201(22-23), 8868-8872, 2007. doi:10.1016/j.surfcoat.2007.04.080

2

R.P. Parikha, R.A. Adomaitis, J.D. Oliverb, B.H. Ponczakb, "Implementation of a geometrically based criterion for film uniformity control in a planetary SiC CVD reactor system", Journal of Process Control, 17(5), 477-488, 2007. doi:10.1016/j.jprocont.2006.04.004

3

T.C. Xenidou, A.G. Boudouvis, D.M. Tsamakis, N.C. Markatos, "An experimentally assisted computational analysis of tin oxide deposition in a cold-wall APCVD reactor", J. Electrochem. Soc. 151(12), C757-C764, 2004. doi:10.1149/1.1809592

4

I.C. Kampolis, K.C. Giannakoglou, "A multilevel approach to single- and multiobjective aerodynamic optimization", Comput. Methods Appl. Mech. Engrg., 2008. doi:10.1016/j.cma.2008.01.015

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