Microwave plasma assisted reactor design for high deposition rate diamond synthesis

Summary form only given. In view of the important, recent, opportunity to commercially synthesize high quality single crystal diamond (SCD) there is a need to continue to improve existing microwave plasma assisted reactor designs that enable high quality and high deposition rate SCD synthesis. It is now widely recognized that both the quality and growth rates of microwave plasma assisted CVD (MPACVD) synthesized diamond are improved by using high power density microwave discharges operating at pressures above 160 Torr [1]. Thus we are developing microwave plasma reactor designs and associated process methods that are both robust and are optimized for high pressure and high power density operation [2], and thereby take advantage of the improved deposition chemistry and physics that exist at high pressures. These reactors operate in the 160-320 Torr pressure regime. Here we describe our the design methodologies, and then we present the specific design details of a 2.45 GHz MPACVD reactor design that enables optimized reactor performance and high growth rate diamond synthesis in the high pressure regime. Reactor design methodologies are described by presenting: (1) a number of visual, numerically calculated, spatial plots of the EM fields inside the cavity applicator as the rector dimensions are varied, and (2) the results from low power (without a discharge) and high power (with discharge) experimental evaluations. From these experimental/numerical investigations a new reactor design evolves that utilizes a hybrid EM cavity applicator mode for discharge excitation. Final reactor designs are determined by observing the reactor performance over the multivariable experimental variable space and performing polycrystalline and single crystal diamond synthesis using CH₄/H₂ input chemistries over the 180-320 pressure regime. High power density discharges are produced with absorbed power densities 150-600 W/cm³. SCD growth rates of 80 microns- hr are achieved and optical quality, type IIa diamond is synthesized.