Properties of linear microwave plasma sustained by coaxial TEM waveguide

A linear 2.45GHz microwave plasma sustained by coaxial circular TEM waveguide has been developed for the low temperature large area plasma enhanced chemical vapor deposition application. TE-TEM microwave power coupling was achieved by copper rod located at $\lambda_{\mathrm{g}}$/4 from short-end of TE$_{10}$ waveguide. TEM waveguide consists of quartz tube surrounded by plasma and copper rod electrode. TEM waveguide is 60 cm in length and 3 cm in diameter, which is terminated with shorted metal cap. For the operation condition of 300 W input power and Ar pressure of 200 mTorr, a clear standing wave pattern with wavelength of 10 cm was observed. Measured plasma density and temperature at 5 cm from quartz wall was 1.2 $\times$ 10$^{17}$/cm$^{3}$ and 1.7 eV respectively. Density non-uniformity was less than 6{\%} along quartz tube in spite of standing wave set-up. In addition, properties of the microwave source are also investigated through electromagnetic field simulation coupled with drift-diffusion approximation of plasma. Calculated and measured standing wave pattern was almost identical. Electron density and temperature distribution show similar behavior with experimental results. S$_{11}$ value of input port of TE$_{10}$ waveguide was calculated as 17dB.