Study On Large Area Plane Surface Wave Plasma Source Driven By UHF Wave

Since the concept of plasma was presented in the 1930s, plasma technique has been wildly used in many fields due to its unique advantages, especially in electronics industry and material science. As the basis of the plasma technique, the research on plasma sources is important. One key problem of the plasma applications is to design and fabricate the plasma source which can generate suitable plasma. Recent years, with the increasing demand for large display panels, solar cells and ultra-large scale integration manufacturing, plasma systems for large area processing has been rapidly progressing. Compare to other plasma sources, surface-wave plasma source has the advantages that can generate high density uniform plasma in a relative large area. But it is often difficult to generate a uniform SWP on a scale of meters by a 2.45 GHz microwave.In this work, we developed a new type large area surface-wave plasma source driven by 915MHz UHF wave. Langmuir probe system was also fabricated for the plasma diagnosis on this device. The main innovative contents in this work are briefly described as following:(1) With the power source replacing from 2.45GHz to 915MHz, larger size waveguide can be used due to the longer free space wavelength of 915MHz wave. It is helpful to produce large area plasma. The other advantage is the cutoff density for 915MHz is about one magnitude lower than that of 2.45GHz. It means the plasma can be sustained in pure surface-wave mode with a lower plasma density, which can help balancing the energy cost for large area discharge.(2) We developed a new cylindrical resonant cavity structure based on the slot antenna theory. Punched plated with quarts windows was employed as the launcher to avoid use an ultra thick quartz plate. During the plasma discharge experiments, we did plasma diagnosis and confirmed the stability of plasma. With the optimization of the launcher structures, finally we get uniform plasma in a radius of 30cm with the electron density around 1011 cm-3 in magnitude.(3) With optimized launcher, we succeeded in plasma surface modification on polyethylene sheets with Ar/NH3 mixed plasma in a radius of 30cm, which is corresponding to the plasma uniform radius measured by Langmuir probe.(4) We simulated the electromagnetic fields distribution in the resonant cavity with 3D-FDTD method. The result indicates that the resonant mode in the cavity is based on TM410. Based on simulation result, we improved the launcher structure and tested the plasma discharge. The plasma density increased about 50% with the similar uniformity at same experiment conditions by using new launcher, which indicates better plasma production efficiency.