Proposal of a means to make the vapor depositions more uniform in a cold wall rectangular CVD reactor at atmospheric pressure - Numerical study

International audienceAt atmospheric pressure, the usual flow conditions in the cold wall horizontal rectangular thermal CVD reactors correspond to stationary longitudinal thermoconvective rolls that make non uniform vapor depositions, in shape of longitudinal parallel ridges. In order to get more uniform depositions, the pressure is generally lowered under the atmospheric pressure to promote forced convection flows, instead of mixed convection ones. In the present paper, using three-dimensional direct numerical simulations and considering the deposition of silicon from hydrogen and silane by the heterogeneous reaction scheme SiH4→Si+2H2, we propose and analyse a simple method to get uniform deposition without lowering the pressure in the reactor. It consists in adequately exciting the parallel thermoconvective rolls at channel inlet to make them unsteady, periodic and sinuous in order to get a uniform time average of the deposition. Two laws for the reaction rate at the susceptor surface are used. They correspond to reaction controlled and diffusion controlled surface reactions. The time averaged deposition rate of silicon is shown to be uniform when the sinuous rolls are fully-developed, whatever the reaction type or the value of the surface Damköhler number