In view of the important, recent, opportunity to commercially synthesize high quality single crystal diamond (SCD) and polycrystalline diamond (PCD), 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. Thus the object of this research is to design, develop, optimize and experimentally evaluate a new generation 2.45 GHz microwave plasma assisted chemical vapor deposition (MPACVD) reactor and associated processes methods that are both robust and are optimized for high pressure and high power density operation, and thereby take advantage of the improved deposition chemistry and physics that exist at high pressures. This MPACVD reactor operates with high power densities and at pressures up to 320 Torr. Differences from earlier MPACVD reactor designs include an increase in applicator and dome radii and the excitation of the applicator with a new hybrid mode. The reactor is experimentally evaluated by synthesizing single crystal diamond (SCD) at pressures from 180-320 Torr with absorbed power densities between 400 to 1000 W/cm3. Without N2 addition SCD growth rates as high as 80 microns/hour were observed. A SCD growth window between 950 °C to 1300 °C was identified and within this growth window growth rates were 1.2-2.5 times greater than the corresponding growth rates for earlier reactor designs. SCD characterization by micro-Raman spectroscopy, SIMS, and by IR-UV transmission spectroscopy indicated that the synthesized SCD quality is that of type IIa diamond.
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