Production of high-density sheet plasma by an rf magnetron device with high-frequency operation

Production of a sheet plasma with a high electron density is successfully realized in an rf magnetron device with a rectangular hollow cathode by operating at a high driving frequency. The electron density ne of the sheet plasma increased up to about 2×1011 cm−3 with the relation of ne∝f2 for f≤20 MHz at a fixed driving voltage, and tended to saturate for f≳20 MHz. This saturation frequency is found to exceed the value in a conventional rf discharge by about four times. A hollow electrode with a size larger than the optimum value decreased the electron density slightly and produced electrons with two temperatures. The frequency dependencies of the rf oscillating potentials at the electrode and in the plasma were also studied to explain the results.