NOZZLE OPTIMIZATION FOR DISSOCIATED SPECIES TRANSPORT IN LOW-PRESSUREPLASMA CHEMICAL-VAPOR-DEPOSITION

Numerical simulation has been used to study the fluid dynamics and che mical kinetics in a supersonic nozzle situated downstream of a plasma reactor. To assist in system scale-up and optimization, effective nozz le design can help in maximizing the transport of chemically active sp ecies to the substrate. This paper examines the chemical non-equilibri um of the flow, the effect of different flow parameters, and the effec t of different nozzle geometries. A three species hydrogen-argon gas m ixture was modeled with finite dissociation and recombination. Non-equ ilibrium transport and thermodynamic mixture properties based on speci es pair collision cross sections were implemented. Running a plasma to rch off design power can significantly alter power losses through the nozzle wall and subsequently change the species distribution at the no zzle exit. Decreasing the effective nozzle throat diameter can notably decrease atomic concentrations. Small changes in upstream or downstre am pressures have a negligible effect on supersonic species transport through the nozzle, Flow separation can be avoided by correctly design ing the divergent portion of the nozzle.