CLUSTER-SIZE DETERMINATION IN THE CHEMICAL-VAPOR-DEPOSITION OF ALUMINUM NITRIDE

Aluminum nitride was prepared in a laminar-flow, tubular reactor using an atmospheric pressure chemical vapor deposition (APCVD) method at a reaction temperature ranging from 700-degrees to 1100-degrees-C and AlCl3 and NH3 concentrations of 0.4 and 8 mol%, respectively. Films grew on the reactor wall and particles formed in the gas phase. The production rates of films and particles were independently determined. A comprehensive model was constructed to estimate the molecular size of the growth species in the APCVD process to simultaneously form films and particles of AlN from AlCl3 and NH3. Transport equations of a dominant growth species used in growing films on the reactor wall and particles in the gas phase in a laminar-flow, tubular reactor were formulated and solved. An assumption made in the model was to use the surface reaction rate constant measured for the film surface for the particle surface. Comparing the film and particle growth data measured experimentally with those obtained from model prediction allows us to conclude that the growth species are clusters ranging in size from 0.8 nm at 700-degrees-C, equivalent to 8 units of AlN, to 0.5 nm at 1100-degrees-C, equivalent to 1 unit of AlN.