High pressure microwave plasma assisted CVD synthesis of diamond

Summary form only given. Microwave plasma assisted CVD (MPACVD) of diamond has received renewed attention during the past several years. The recent experiments by Yan et al. (2002) have demonstrated the synthesis of high quality single crystal diamond with growth rates from 10 to over 100 mum/hr with operating pressures of 110-180 torr. High pressure operation allows higher reaction species concentrations and increase deposition rates. Currently, most commercial microwave plasma deposition reactors are designed for operation up to 120 torr and thus this reactor technology is not optimally designed for operation in the 120-300 torr pressure regime. High pressure operation allows higher reaction species concentrations and increase deposition rates. Hence, the objective of this research is to explore the behavior of microwave discharges between 180-300 torr and to learn how to control and efficiently couple to them to enable high pressure MPACVD diamond synthesis. This investigation explores the performance of a microwave cavity reactor (K. P. Kuo and Jes Asmussen, 1997) that has been modified to operate in the higher pressure regime. Major modification of the reactor include the redesign of the substrate holder, cooling stage and gas flow patterns to enhance the plasma power density, stability and also to enable operation from 180-300 torr. The polycrystalline and single crystal diamond films are synthesized using methane/hydrogen gas mixtures. The microwave input power ranges from 1.5-3 kW, gas chemistry 2-10% CH₄/H₂, and operating pressure from 180 to 300 torr. The substrate holder is water cooled to maintain the deposition temperature of 950-1250degC. The substrate materials are either a one inch silicon wafer or HPHT single crystal diamond seeds. Experimentally measured deposition rates, plasma power densities, optical emission spectroscopy measurements of the discharge temperature and radical species densities versus operating pressure, inpu- - t power, and gas chemistry are presented. Measured discharge absorbed power densities range from 160-500 W/cm³ as the operating pressure increases and the diamond growth rate increases with increasing power density, operating pressure and higher methane concentration. Depending on the input experimental conditions, the diamond growth rate ranges from 3-50 mum/hr. Methods of achieving deposition uniformity, plasma stability, and long term operation of the reactor will be presented.