Rotating Surface Wave Excitation by Time-varying Phase Agitation and Amplitude Modulation using Cylindrical Resonator

As a planar-type microwave plasma source, surface wave plasma (SWP) which generates a specific wave mode between the plasma and a dielectric plate is mainly used. To improve plasma uniformity, it is necessary to improve the uniformity of the electric field at dielectric surface. For this purpose, a microwave source which uses rotating surface wave excitation has been developed. A higher-order mode (TE₁₃₀) cylindrical cavity resonator is used for plasma generation. Electromagnetic waves generated by individual magnetron systems (phase-locked, 2.458 GHz) propagate to the cylindrical resonator via two different input ports at orthogonal positions. The cavity field rotates orthogonally when the phase difference (ϕ) is π, depending on the phase agitation frequency (~5 kHz). Based on the electric field distribution of the pill-box cavity, electromagnetic waves propagate through a hybrid type slot antenna composed of a ring and a large aperture structure. The electric field distribution of the surface wave (TM mode) formed on the dielectric window surface also rotates according to the change of phase difference. This effect is experimentally confirmed in Ar plasma at 0.1~1 Torr with total injection powers from 0.6 to 1.5 kW, which shows plasma uniformity is improved.