关键词: 驻波/
均匀性/
波诊断
English Abstract
Effect of standing wave on the uniformity of a low magnetic field helicon plasma
Niu Chen,Liu Zhong-Wei,
Yang Li-Zhen,
Chen Qiang
1.Lab of plasma physics and materials, Beijing Institute of graphic communication, Beijing 102600, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos.11375031,11505013) and the Beijing Municipal National Science Foundation,China (Grant Nos.4162024,KZ201510015014,KZ04190116009/001,KM201510015009,KM201510015002).Received Date:16 October 2016
Accepted Date:23 November 2016
Published Online:05 February 2017
Abstract:Helicon wave discharge has higher coupling efficiency than capactively coupled and inductively coupled discharge in low static magnetic field. In the wave sustained mode, a large volume and large area plasma can be produced at lower pressure by using comparable discharge power, and thus it expands the helicon wave plasma applications in material surface modification, thin film deposition, dry etching and thruster usage. However, the application of helicon wave source still faces challenges, such as the controversial power coupling mechanism, operation stability and the plasma distribution uniformity in the experiment. The wave mode existing in bounded helicon wave plasma column generally consists of helicon and Trivelpiece-Gould (TG) components, and their mode transitions and different transverse wave field distribution regions, and the propagating characteristic of the helicon wave are directly related to the power coupling and plasma density distribution in the source region, then affect the uniformity of material processing and film deposition in the diffusion chamber. In this paper, the plasma azimuthal non-uniformity, with using Doubble Saddle antenna, 100 G static magnetic field in helicon wave plasma source, is studied by electrical characteristic (power-current) curve, intensified charge coupled device (ICCD) image and magnetic probe measurements. The electrical characteristic curve indicates two discharge stages with different effective resistances. Meanwhile, in the second stage, the higher effective resistance would result in higher coupling efficiency and higher plasma density. But the ICCD image demonstrates the azimuthal non-uniformity of plasma, indicating that the main heating points at the diagonal edge are linked to the stationary transverse electrical field line pattern of azimuthal mode number m=+1 helicon wave, and the magnetic probe is used to measure the helicon wave magnetic field Bz component along the quartz source tube axially. The magnetic probe results show that the standing wave appearing below the antenna even though in the upper region of the antenna is characteristic of the traveling wave. Furthermore, at the plasma boundary, the standing wave can be coupled to the TG wave, and not like travelling wave it has no angular rotation of the electric field and may cause the non-uniform coupling between the helicon and TG components. The TG wave then has azimuthal non-uniform electron heating. Therefore, the standing helicon wave below the antenna is the key factor to the plasma non-uniformity problem. Changing the propagating characteristics of the helicon wave further in the plasma column will be of positive significance for optimizing the discharge efficiency of the plasma source and controlling the plasma distribution uniformity, stability and other operations as well.
Keywords: standing wave/
uniformity/
wave diagnostic
