A Linear Microwave Plasma Source Using a Circular Waveguide Filled with a Relatively High-Permittivity Dielectric: Comparison with a Conventional Quasi-Coaxial Line Waveguide

Ju-Hong Cha,Ho-Jun Lee,Sang-Woo Kim

doi:10.3390/app11125358

Abstract

For a conventional linear microwave plasma source (LMPS) with a quasi-coaxial line transverse electromagnetic (TEM) waveguide, a linearly extended plasma is sustained by the surface wave outside the tube. Due to the characteristics of the quasi-coaxial line MPS, it is easy to generate a uniform plasma with radially omnidirectional surfaces, but it is difficult to maximize the electron density in a curved selected region. For the purpose of concentrating the plasma density in the deposition area, a novel LMPS which is suitable for curved structure deposition has been developed and compared with the conventional LMPS. As the shape of a circular waveguide, it is filled with relatively high-permittivity dielectric instead of a quasi-coaxial line waveguide. Microwave power at 2.45 GHz is transferred to the plasma through the continuous cylindrical-slotted line antenna, and the radiated electric field in the radial direction is made almost parallel to the tangential plane of the window surface. This research includes the advanced 3D numerical analysis and compares the results with the experiment. It shows that the electron density in the deposition area is higher than that of the conventional quasi-coaxial line plasma MPS.

Highlights

Microwave plasma sources (MPSs) are driven by applied frequencies of 1–100 GHz and lead to electron heating and excitation of a discharge from the electromagnetic waves that either penetrate the plasma or exist along the surface [1,2]
Excitationis based on the electric field profiles, and in this study, the wave field was fed by a wave state species, which means electron heating occurs
In the linear applied power to onein side power absorption along the wave propagation which could in a specific port, electron density attenuation appeared along direction, the linear axis due to theresult difference in the electron density distribution

Summary

Introduction

Microwave plasma sources (MPSs) are driven by applied frequencies of 1–100 GHz and lead to electron heating and excitation of a discharge from the electromagnetic waves that either penetrate the plasma or exist along the surface [1,2]. With weakly ionized MPS used for material processing, waves are important to transfer energy from the excited surface of the waveguiding structure to the bulk plasma, where the wave energy is absorbed [3]. The main element of the MPS, for material processing, is the microwave-to-plasma applicator because it determines the structure of the electromagnetic field in the plasma as well as the absorption energy efficiency of plasma [4]. The energy absorption efficiency of MPS is determined by the wave penetration depth in the plasma, wave field strength at the plasma surface, and waveguiding structure. The plasma is generated by the waves emitted from the dielectric surface which replaces a part of the waveguiding structure

Methods

Results

Conclusion