Abstract
Microwave linear plasma has attracted a lot of attention due to the outstanding characteristics such as high electron density, low electron temperature, no-pollution, and homogenization, which can realize a large-area uniform plasma source through vertical or horizontal arrangement especially. In order to explore the effect of the permanent magnets and the microwave coaxial reflective antenna on density and uniformity of plasma, a three-dimensional numerical model is established. It is expected to obtain a superior microwave linear plasma source with high density and uniformity for fabricating a carbon film such as graphene or surface treatment. The results show that (1) permanent magnets can improve the density and uniformity of plasma by generating a suitable magnetic field. At the microwave power of 800 W at 20 Pa, the permanent magnets with 150 kA/m enhance the average electron density by 36.67% and control the relative deviation of electron density within −3% to 1% at an axial distance of 100 mm–300 mm. (2) The reflective antenna can effectively regulate the shape and the uniformity of plasma. The semicylinder reflective antenna realizes the relative deviation of electron density within −2% to 0.5%. Meanwhile, the average electron density increases by 3.75% between an axial distance of 100 mm and 300 mm under a microwave power of 800 W at 20 Pa. (3) The external magnetic field and reflective antenna also have the regulation on heavy particles (Ars) in plasma, which is an important factor for application.
Highlights
Microwave discharge plasma is widely applied in the field of material synthesis, surface modification, etc.,[1,2,3,4,5,6] because of many outstanding characteristics such as high electron density, stability, no-pollution, and good controllability.[7,8] In 1997, Petasch et al.[9] designed a device to generate microwave plasma that expanded linearly which tends to achieve outstanding axial uniformity of electron density
The standing wave effect is presented clearly in the distribution of heavy particles. It can be seen intuitively from the cloud diagram that the magnetic field and the reflective antenna both have a direct influence on heavy particles (Ars), which means that the regulation can be achieved
The external magnetic field generated by permanent magnets has an advantageous effect on the density and uniformity of plasma, the same as with the microwave reflective antenna
Summary
Microwave discharge plasma is widely applied in the field of material synthesis, surface modification, etc.,[1,2,3,4,5,6] because of many outstanding characteristics such as high electron density, stability, no-pollution, and good controllability.[7,8] In 1997, Petasch et al.[9] designed a device to generate microwave plasma that expanded linearly which tends to achieve outstanding axial uniformity of electron density. Yamada et al.[15] obtained high quality and large area graphene films by combining several linear microwave plasma sources in the roll-to-roll process under the pressure of 30–300 pa. It is known that an external magnetic field effectively promotes plasma density.[16–18]. Xiaobao et al.[25] developed a large area microwave plasma by using the slot antenna and the maximum ion density was 4.3 × 1016 m−3 at 400 Pa. Kanoh et al.[26] obtained a stable and uniform argon plasma with electron density in the order of 1017 m−3 by introducing the optimized slot antenna at a processing pressure of 70 Pa. Obrusník and Bonaventura[23] demonstrated the influence of the antenna shielding on the hydrogen plasma and particles by a mixed 2D/3D fluid model.
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