Continuous chemical vapor deposition processing with a moving finite thickness susceptor

Abstract

Chemical vapor deposition (CVD) of thin films onto a moving surface is an important material processing technique for semiconductor fabrication, optical coatings, and many other applications. Continuous CVD processing offers an attractive solution to meet high volume requirements. In this study, the deposition on a finite thickness moving susceptor, considering surface reactions, is numerically investigated. When a susceptor is in motion, the reaction zone residence time and the coupling of conduction heat transfer in the susceptor with convection heat transfer in the gas flow significantly alter the deposition rate and film quality. A model is developed to quantify continuous CVD film production for several important design parameters. The numerical model is validated for the deposition of silicon through comparisons with analytical results and experimental data available in the literature. Films produced by continuous CVD are shown to be strongly dependent on susceptor speed, material selection, and susceptor thickness. Susceptor speed is directly linked to residence time in the reaction region, with lower residence times resulting in less time for reaction and heating, hence reducing growth rates. Increased thickness and susceptor thermal diffusivity alters the thermal energy distribution, thereby reducing the susceptor surface temperature and lowering the deposition rate. These effects may be overcome by increasing the length of the heating zone. Film quality is also influenced by the susceptor temperature, since reaction-controlled deposition typically produces different film structure than deposition under diffusion-controlled conditions. Overall, the results obtained demonstrate the feasibility of employing a moving finite thickness susceptor for CVD processing. A correlation of several operational parameters is also obtained for the film thickness. This may be used for the design and optimization of continuous CVD systems. The numerical model may also be used for considering deposition of other materials.