Simulation Of The Temperature And Flow Field In HFCVD System

Temperature distribution and flow field of the system, to a great extent, significantly affect the nucleation density and growth velocity of diamond film over large area by Hot Filament Chemical Vapor Deposition (HFCVD). In this paper, the influence of various deposition parameters on the temperature and flow field is investigated. Then the parameters are optimized for the growth of diamond film over large area. The main works are as follows:1. H₂ is chosen as the main research object of fluid in HFCVD system. It is calculated that the Reynolds number is 979.3 and the Mach number is 0.05. Therefore, the flow regime is laminar, incompressible and low-speed flow.2. Multipoint temperature of the planar substrate with the diameter of 80 millimeter is measured by the K-thermocouple. And the temperature distribution curve of the substrate surface is attained. Then using the 3D finite element (FE) model of filaments and substrate in ANSYS, the influence of the hot filaments parameters and thermal contact resistance on substrate temperature is simulated in detail. According to the results, when the effect of 3D-substrate heat conduction and the nonuniform filament temperature distribution are considered, the substrate temperature field is more uniform than in pure heat radiation system.3. Using the 2D thermal-flow coupled model of the hot filaments, substrate and H2 in FLOTRAN CFD, the effect of different deposition parameters on the system temperature and flow field is simulated. The results reveal that the high temperature of hot filament array leads to thermal round-flow of gas which can't be ignored in the growth of diamond film.4. The optimized deposition parameters based on the simulation results are: the number of the hot filaments is 14, the radius of the hot filaments is 0.3 millimeter, the distance between the hot filaments and substrate is 5 millimeter, the distance between the hot filaments is 6 millimeter, the velocity of the gas inlet is 2.36 meter per second, and the number of the gas inlets is 1. The high quality diamond film of 80 millimeter diameter deposited in HFCVD system is obtained using the optimized deposition parameters. The polycrystalline diamond film presents the (100) facets in the center and (111) facets in the fringe. And the growth rate of the diamond film in the center is lower than that in the fringe, which is consist with the simulation result.5. Based on the research of the temperature distribution of the planar substrate, the simulations of spherical substrate and wire drawing die HFCVD system are developed. According to the temperature field, it is feasible to deposit diamond films on the spherical substrate and wire drawing die.