Spectral measurements of inductively coupled and m = +1, −1 helicon discharge modes of the constructed plasma source

Mohammadreza Khoshhal,Rod Boswell,Morteza Habibi

doi:10.1063/1.5140346

Mohammadreza Khoshhal, Rod Boswell + Show 1 more

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https://doi.org/10.1063/1.5140346

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Abstract

In the present context, the industrial type of Amirkabir helicon plasma source has been introduced that was designed and constructed at the Helicon Plasma Laboratory of Amirkabir University of Technology with the aim of using it in material processing applications. Helicon plasma in two m = +1 and m = −1 modes of operation was studied, and also its application was compared with the inductively coupled plasma (ICP) mode in this experimental work. This study was performed by employing two techniques including optical emission spectroscopy and imaging using a camera with polarizing filters, in which the images and spectra of ICP and m = +1, −1 helicon plasma modes were recorded under the experimental conditions. The effects of the device operational parameters on the argon plasma emission spectra were investigated in the wavelength range of 350–950 nm. It was observed from the comparison of the plasma spectra that the ionization rate increases significantly for the plasma helicon mode than ICP and also for m = +1 helicon mode of operation than m = −1. In this work, the values of device operational parameters such as the RF power delivered to the half-helix antenna, external magnetic field intensity, and the injected gas flow rate were varied in the range of 400–900 W, 100–300 mT, and 1–10 SCCM in the experiment, respectively. In addition, the optimum values of RF power, magnetic field intensity, and the injected gas flow rate for achieving the maximum ionization rate were, respectively, obtained as 900 W, 300 mT, and 3 SCCM.

Highlights

Helicon waves have been studied in two aspects of theories1,2 and experiments,3,4 which were carried out in gas and solid plasmas.The new era of helicon wave investigation began when Boswell3,5 successfully used helicon waves for the generation of high density plasma (∼4 × 1018 m−3) in a cylindrical glass tube in a 75 mT axial magnetic field at the applied 600 W RF power
The minimum and maximum strength of the axial magnetic field in the antenna region for 100 A Direct Current (DC) current was obtained as 100 mT and 300 mT, respectively
It has been shown that the reddish color of the plasma was changed and the blue core appeared when the plasma was magnetized due to the external magnetic field and the RF power increased to 400 W in the 3 SCCM argon flow rate

Summary

Introduction

The new era of helicon wave investigation began when Boswell successfully used helicon waves for the generation of high density plasma (∼4 × 1018 m−3) in a cylindrical glass tube in a 75 mT axial magnetic field at the applied 600 W RF power. This valuable work leads to the generation of plasma that has at least an order increased density than the RF conventional plasmas under the same power conditions.. In the Inductively Coupled Plasma (ICP) sources, a helical shaped coil surrounding plasma generation region generates a time-varying magnetic field when it is supplied by RF currents. The generation of this magnetic field in the mentioned region leads to the induction of the solenoidal RF scitation.org/journal/adv electric field that causes acceleration of free electrons and plasma formation.

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