The main objectives of this dissertation research were to evaluate the existing microwave plasma assisted chemical vapor deposition (MPACVD) Reactor B in the high pressure regime of 180-280 torr by experimentally investigating single crystal diamond (SCD) synthesis, and experimentally defining the safe, efficient and stable process window for high growth rate high quality SCD production.An experimental methodology was developed that determined the safe and efficient operating regime for Reactor B. This methodology first defined the nonlinear relationships between the input power, discharge average power density, pressure and substrate temperature; i.e. it established an operating field map at high pressure and power densities for Reactor B. Then a safe and efficient reactor operating variables space over the 180-280 torr pressure regime was identified within the operating field map. When operating within these conditions, discharge power density was increased to 100-600 W/cm3 by increasing the operating pressure, reactor wall reactions were also minimized, and the safe, efficient and low maintenance operation of Reactor B was enabled over a wide range of operating conditions.For Reactor B the operating field map and the safe and efficient operating regime was specifically defined for SCD synthesis. While operating within a safe and efficient reactor operating window, SCD synthesis was experimentally demonstrated from 180 to 280 torr. At a constant pressure of 240 torr a high quality, high growth rate SCD substrate temperature window was experimentally identified between 1030 and 1250 °C. In particular using feed gases with nitrogen impurity levels of less than 10 ppm SCD was synthesized with growth rates of 20-45 μm/h.The SCD synthesis experiments demonstrated that as the pressure and discharge absorbed power density increased the diamond deposition rate increased. Diamond synthesis rates and quality surpass those that were achieved by synthesizing SCD at lower pressure and with earlier reactor technologies. As pressure was increased the experimental variable window to grow high quality diamond also expanded and larger methane concentrations (5-7%) were able to synthesize high quality diamond. When nitrogen impurity levels were reduced below 10 ppm in the gas phase the quality of the synthesized diamond was of type IIa or better. After laser cutting and polishing high quality diamond plates were synthesized. These experiments demonstrated that MPACVD diamond synthesis rates and diamond quality increased and improved respectively as the operating pressure increased.
Read
