Scaling behavior of microwave reactors and discharge size for diamond deposition

Several microwave reactors of various sizes were studied to quantify the size scaling behavior of microwave plasma-assisted CVD (PACVD) diamond deposition. All the systems studied were microwave resonant cavity based systems using predominantly hydrogen based discharges. The input variables considered include the microwave frequency (2.45 GHz and 915 MHz), the microwave power level, and the discharge chamber size (5-28 cm diameter). The substrate sizes for the various reactors studied ranged from 2.5 cm diameter substrates for the small reactor size to 15 cm diameter substrates for the large reactor size. The variables quantified in the diamond deposition process and reactor included the microwave discharge power density, discharge size, discharge gas temperature, as well as, measurements of diamond deposition area and rate. The discharge power density versus pressure and discharge size is quantified by experimental measurements and numerical modeling. Results show that as the discharge size increases the discharge power density decreases significantly at a given pressure.