Brownian dynamics study of particles in chemical vapor deposition of aluminum nitride

Aluminum nitride (AlN) films are commercially grown by chemical vapor deposition. In this process, it has been experimentally observed that AlN nanoparticles are formed in the gas-phase. Although these particles are formed in the vicinity of the hot substrate, they tend to stay away from the hot substrate and are observed to deposit on the cold walls of the reactor. In this study, the trajectories of the AlN particles are simulated with the goal to understand the mechanisms responsible for their motion. A three-dimensional (3D) Lagrangian Brownian dynamics simulator based on the Langevin equation is developed, and coupled with a 3D computational fluid dynamics (CFD) solver. The model is validated, and then explored for the problem at hand. It is found that thermophoretic forces are primarily responsible for driving the particles away from the hot substrate and depositing them on the cold reactor walls.