Method of power density determination in microwave discharge, sustained in hydrogen–methane gas mixture

•Method of power density determination in MPA CVD reactors for diamond growth•Use of photos of the discharge made with Ha filter for plasma volume determination•Power density determined in pressure range 80 - 350 Torr was 50 to 550 W/cm3

We present the results of studying a continuous microwave discharge maintained at a frequency of 2.45 GHz in a CVD reactor based on a cylindrical resonator excited at the TM013 mode. The discharge was ignited in hydrogen and a gaseous mixture of hydrogen and methane and was studied by the method of optical emission spectroscopy. Density of atomic hydrogen and gas temperature were measured, as well as the spatial distribution of both optical emission intensity of the plasma and intensity of the Hα line of atomic hydrogen. The main parameters of the discharge were calculated numerically using the two-dimensional self-consistent model of the discharge. Basing on the obtained results, we proposed a method for high-precision experimental determination of the plasma volume and calculation of the specific energy contribution to the plasma, i.e., microwave power density in plasma (MWPD), with minimal errors. According to the calculations, in the experiment performed, the microwave power density in the plasma varied from 50 to 550 W/cm3 as the gas pressure increased from 80 to 350 Torr. The method allows one to perform unified MWPD calculations in different CVD reactors and to compare diamond film deposition regimes.

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