Oxygen Microwave Plasma Density Enhancement by Surface Waves with a High-Permittivity Material Window

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Abstract
The oxygen microwave plasma properties caused by surface waves in high-permittivity materials of alumina and quartz windows were studied for large-diameter plasma generation. The electron density value for the alumina window at microwave powers above 450 W is significantly enhanced by surface waves and is considered to be in a surface-wave mode. The electron density value for the quartz window at powers above 250 W is also in the surface-wave mode. In the surface-wave mode, the electron temperature values are lower than those in the volume mode which is not affected by surface waves, and the intensity values of the built-in high-frequency magnetic field decrease rapidly at a distance of 7–10 cm from the bottom surfaces of the windows. Plasma emission modes for the alumina window are in the (0,1) mode at low pressure (13.3, 33.9 Pa) and the multiple mode at high pressures (66.5, 133 Pa). On the contrary, plasma emission modes for the quartz window are in the multiple mode at high pressures and the (0,1) mode at low pressures. Uniformity of the plasma density distribution in the multiple mode is better than that in the (0,1) mode at identical pressures.