The Research Of Surface-wave Plasma Generated By Cylindrical Dielectric Waveguide

As the plasma science develops further, plasma technology has been applied widely in variety of domains, especially in integrated circuit and material process. As the basis of plasma science, plasma source is the key factor of plasma science. Compare with other plasma sources, surface wave plasma source is more suitable for plasma treatment because of high density, uniform space, high activity and flexibility. Recent years, the research on surface wave plasma source has been mainly focused on plasma source with planar dielectric waveguide. However, plasma source excited by cylindrical dielectric waveguide has been reported rarely, which has the unique advantages in special applications requiring vertical processing or inner wall of tube.In this work, a new cylindrical surface-wave plasma generator has been set up, based on guided modes of cylindrical dielectric. Langmuir probe system was also fabricated for plasma diagnosis on this plasma source. The main innovative contents in this work are shown as following:First, cylindrical quartz rod has taken the place of traditional planar dielectric. When the discharge power was 450W, the plasma with high electron density 3×1011 cm-3 near the rod surface and 45cm in length could be excited along the rod, which verifies this type of plasma source can meet the need of plasma treatment in vertical direction, especially the inner wall of tube.Second, based on the theory of cylindrical dielectric waveguide, the transmission mode of cylindrical rod has been analyzed. Distribution of electron density and temperature were diagnosed by Langmuir probe. The electron density decreases proportionally in radial direction while electron temperature decreases exponentially. Both increase when microwave power increases. On the other side, electron temperature and density are both down along the axial direction. When air pressure decreases from 40 Pa to 20 Pa, electron density is up but electron temperature gets lower due to the weak electron diffusion at high pressure. We also found dielectric rod with higher permittivity could generate pure surface wave plasma with higher density.Third, visible surface plasmon polariton (SPP) phenomenon is observed on the surface of cylindrical conductor for the first time. According to similar feature between high density plasma and metal when interacts with electromagnetic wave, we propose that SPP can be excited at the boundary between plasma and dielectric rod. the critical electron density of SPP is about 2.37×1011 cm-3. In order to observe SPP at the boundary between plasma and dielectric rod, we make the electron density exceed that threshold value near the surface of dielectric conductor by change discharge power, and thus SPP occurs. Experiments demonstrate that wavelength of illuminating waveform on the boundary is in line with theoretical SPP wavelength as plasma density changes.Another research is about surface modification of Indium Tin Oxide (ITO) film by plasma ion immersion implantation (PHI). In order to raise ITO work function, it has been well discussed the improvement of ITO treated by PHI. The details are as follows:Self-designed PHI system is applied in ITO treatment for the first time. All of parameters are optimized to obtain the best treatment condition, such as biased potential, treating duration and pulse width. Besides, PHI treatment is compared with ultrasonic pretreatment and oxygen plasma treatment by indexes. As a result, oxygen PHI not only maintains crystal orientation, transparency, surface resistance, and morphology, but also heightens surface work function by effectively eliminating pollution and increasing oxygen concentration. Experiments also prove that oxygen PⅢ is more effective in improving ITO surface than O-ICP.A theoretical explanation is proposed about PⅢ improving ITO surface work function. Oxygen atoms in environment can be adsorbed by surface of ITO and occupy holes in ITO, which decreases carrier concentration, reduces Fermi level. That hypothesis can logically explain why oxygen PⅢ can significantly increase surface work function.