TRANSPORT IN CHEMICAL VAPOR DEPOSITION REACTORS: A TWO-DIMENSIONAL MODEL INCLUDING MULTICOMPONENT AND THERMAL DIFFUSION, AND SPECIES INTERDIFFUSION

摘要

The chemical vapor deposition (CVD) process that consists of depositing coatings of silicon nitride from silicon tetrafluoride and ammonia at low-pressure is modeled in a two-dimensional reactor simulation. The combined effects of surface chemical kinetics, multicomponent diffusion, convection, thermal diffusion, species interdiffusion, and variable properties are included for the first time in a two-dimensional reactor model. Full multicomponent diffusion is included by solving the Stefan-Maxwell equations. Species interdiffusion and thermal diffusion are included in the energy and species conservation equations, respectively. The present results are for five gas phase species with two surface reactions specified for the deposition. Distributions of the radial and axial components of velocity, species, temperature, and deposition rate and deposition profile are obtained in a tube reactor. The effects of the combined transport mechanisms noted above are determined and elucidated. The decomposition of NH{sub}3 into N{sub}2 and H{sub}2 retards the deposition of silicon nitride and dilutes the incoming reactants. This dilution is strongly enhanced by thermal diffusion since the direction of the temperature gradient causes the light species generated by the surface reactions to remain near the surface resulting in smaller and nonmonotonic deposition rates. The effects of a ramp in the surface temperature on the deposition rate and profile and on the transport processes are also determined.