Study of magnetic field influence on charged species in a low pressure helicon reactor
Résumé
The variation of electron density (n e), ion flux and emission of argon lines were investigated in a rf helicon reactor for different static magnetic field amplitude and rf power using Langmuir probe, rf coupled planar probe and optical emission spectroscopy (OES). The static magnetic field was created by two Helmholtz coils positioned around the plasma source. Its amplitude B varied by changing the current I B = 0 ÷ 2 A through the coils from 0 to 10 mT (0 ÷ 100 Gauss) in the helicon source, which corresponded to 0 ÷ 1.4 mT (0 ÷ 14 Gauss) in the diffusion chamber. We studied Ar and O2 discharges at 0.7 Pa with rf power 50 ÷ 600 W applied to the helicon antenna. The variations of n e, ion flux and intensity of Ar 750 nm with the rf power measured in Ar diffusion plasma were in a good agreement. It was found that n e increased monotonically with the rf power for I B < 1 A whereas for higher current it exhibited a maximum, which position shifted from lower to higher rf power with increasing I B. The OES measurements in the plasma source for I B = 1.5 A showed that the Ar emission line did not reach a maximum but continuously increased with the rf power. Hence, it is concluded that the maximum observed for n e in the diffusion chamber is likely to be due to some confinement of the plasma in the source. Measurements in oxygen discharge showed slightly different results.
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