High-density plasma production using a slotted helical antenna at high microwave power

Abstract

This paper presents results of high-density plasma production experiments carried out using an optimally designed and excited slotted helical antenna. The slotted helical antenna was excited by linearly polarized, right-hand polarized (RHP) and left-hand polarized (LHP) CW microwaves (f = 2.45 GHz) with power up to 2.5 kW. Two different discharges-the resonant and the non-resonant discharges-were studied. In the resonant discharges the magnetic field at the edge of the helical antenna was equal to the ECR field, so that a resonant coupling of the electrons and the microwaves could occur. In non-resonant discharges the value of the magnetic field was greater than the resonant field throughout the mirror. It was seen that the linearly polarized and RHP waves can produce about 100% ionization (at pressures ≈ 1-2 × 10 −4 Torr; power ≤ 2.5 kW) for both resonant and non-resonant discharges. In most cases an enhancement over the neutral particle density could be observed due to improved confinement. The resonant discharge using LHP waves also yielded similar results as obtained using the RHP and the linearly polarized waves. This result is somewhat unexpected since the LHP waves are not expected to undergo resonance at electron cyclotron resonance. The non-resonant discharge using LHP waves was found to be very weak (underdense). Finally, an attempt has been made to understand the unexpected nature of the resonant discharges using LHP waves, in terms of the modes of plasma loaded helices and waveguides.

Evidence of current free double layer in high density helicon discharge

“…One may improve the situation somewhat by using a magnetic mirror configuration as used in authors' work on electron cyclotron resonance and helicon plasma production. [46][47][48][49][50] Therefore, for the present experiments, use of a magnetic mirror configuration has been necessary for trapping the population of nonthermal electrons.…”

Role of peripheral vacuum regions in the control of the electron cyclotron resonance plasma uniformity

“…[1][2][3][4] We have already reported the experiments, 5 which indicated that the electric field strength of the extraordinary wave ͑the X wave͒ was small around the center of the uniform plasma, and became large at the radial edge of the plasma. Furthermore, recent numerical results [6][7][8] show evidence for the propagation or, absorption of the lefthanded circularly polarized wave ͑the L wave 9 ͒ or other modes in the ECR plasma even on the condition; that the magnetic field strength is greater than the ECR condition (/ ce Ͻ1) or that the electron plasma frequency is higher than the wave frequency (/ pe Ͻ1). Recently, electromagnetic waves that propagate up to the outside ECR region have been giving some attention in a numerical simulation for plasma processing.…”

Theory of high-frequency guided waves in a plasma-loaded waveguide

“…[2][3][4] While the first two populations are isotropic 13 with T r ϭT ʈ /T Ќ Ϸ1[T ʈ (T Ќ ): parallel ͑perpendicular͒ temperature͔, the warm electron population is anisotropic. Although a small warm electron component is not expected to influence significantly the nature of the guided modes in a plasma-loaded guide, the present study does include two electron populations ͑without any restrictions on their isotropicities and densities͒ keeping future applications in mind.…”