Particle mobilization in pecvd reactor using thermophoretic force

Summary form only given. Plasma enhanced chemical vapor deposition (PECVD) for the coating of micron and submicron sized particles, the idea of which originated from the behavior of plasma-generated particles in microelectronics fabrication, offers several advantages as compared to more traditional approaches. The particles are negatively charged, which prevents their agglomeration. Further, operating at room temperatures creates the possibility of coating a larger variety of materials. In the related experiments it has repeatedly been demonstrated that particles released from the upper electrode, ultimately levitate in the vicinity (sheath-bulk interface) of the lower electrode as a result of balance in electric, gravitational, and ion drag forces. As long as the particle resides in this region, deposition process proceeds through the diffusion of species. The intrinsic nonhomogeneous nature of plasma structure in this region leads to the directional variation of radicals fluxes toward the particle, and thus nonuniform coating thickness appears on the particle. Jellum et al. visualized the effect of thermophoretic force associated with gradients in neutral gas temperature in particulate-contaminated discharges. It was observed that particles tend to move away from the heated electrode towards the cooled one. In this work, we use numerical simulations to propose a feasible method, based on alternative heating and cooling of either of the electrodes, to mobilize the particles in the reactor and control their motion between the upper and lower electrodes as a means to overcome the above-mentioned problem in PECVD technique. We simulate a parallel-plate geometry, low-pressure RF plasma reactor via local field equilibrium approximation by means of numerically solving drift-diffusion model equations. Then, employing the time-averaged plasma variables, we track a single particle injected into the reactor from the top electrode in a Lagrangian framework, while taking into- account various forces and charging process for the particle. We show that after the particle reaches its equilibrium position in the sheath, by applying the thermophoretic force through heating the corresponding electrode, it is possible to make the particle move through the bulk plasma and reach the sheath on the opposite side of the reactor. This motion of the particle facilitates more homogeneous coating