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Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide
Published in Mohamed Gad-el-Hak, MEMS, 2005
Glenn M. Beheim, Laura J. Evans
There are a number of different HDP systems, including magnetically enhanced RIE (MERIE), electron cyclotron resonance (ECR), helicon, and inductively coupled plasma (ICP) systems. MERIE systems use a magnetic field to confine electrons to the plasma. This situation enhances the plasma density but usually negatively affects the uniformity. In an ECR system, plasma electrons are confined using strong magnets and excited at the electron cyclotron frequency using microwaves. A field of 875 G is required to achieve resonance at the commonly used microwave frequency of 2.45 GHz. In a helicon reactor, a helicon wave is excited using an RF-driven antenna (typically 1-50 MHz) in conjunction with a relatively weak magnetic field (typically 20 to 200 G). This system creates a high-density, uniform plasma, but the chamber has a large aspect ratio. Detailed information about different HDP systems has been provided by Lieberman [1994]. Inductively coupled plasma has come to dominate the HDP market, largely as a result of lower complexity and cost. An ICP reactor will be discussed in further detail.
Conceptual Design of a Permanent Ring Magnet-Based Helicon Plasma Source
Published in B. Raneesh, Nandakumar Kalarikkal, Jemy James, Anju K. Nair, Plasma and Fusion Science, 2018
Arun Pandey, Dass Sudhir, M. Bandyopadhyay, A. Chakraborty
Helicon plasma sources are very promising plasma sources due to their high ionization efficiency [1]. The physics behind such high efficiency is still a subject of investigation. However, due to having high plasma density (~ 1013 cm-3) using low RF power (~ few kW), helicon based plasma sources are used in the fields of plasma processing [2] and space exploration [3].
Plasma Created in High-Frequency Electromagnetic Fields
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
Another high-density plasma (HDP) discharge, that can be used for different material processing applications, is the helicon discharge. The HDP-plasma generation in the helicon discharge was first investigated by R.W. Boswell, 1970. The detailed theory of this discharge, and the general propagation and absorption of the helicon mode in plasma was developed by F.F. Chen, 1991. Helicon discharges are sustained by electromagnetic waves propagating in magnetized plasma in the so-called helicon modes. The driving frequency in these discharges is typically in the radio-frequency range of 1−50 MHz (the industrial radio-frequency 13.56 MHz is commonly used for material processing discharges). It is interesting to note that in contrast to the RF-discharges considered in sections 10.3–10.7, the helicon discharges can be considered as wave heated even though they operate in the radio-frequency range. This can be explained taking into account that the phase velocity of electromagnetic waves in magnetized plasma can be much lower than the speed of light (see Sections 6.6.7 and 10.8.5). This provides the possibility to operate in a wave propagation regime with wavelengths comparable with the discharge system size even at radio frequencies, which are much below the microwave frequency range. The magnetic field in helicon discharges applied for material processing varies from 20 to 200 G (for fundamental plasma studies it reaches 1000 G), and it is much below the level of magnetic fields applied in ECR-microwave discharges. Application of lower magnetic fields is an advantage of the helicon discharges. Plasma density in these wave-heated discharges applied for material processing is about 1011−1012 cm−3, but in some special cases can reach very high values of about 1013−1014 cm−3 . Excitation of the helicon wave is provided by an RF-antenna that couples to the transverse mode structure across an insulating chamber wall. The electromagnetic wave mode then propagates along the plasma column in the magnetic field, and plasma electrons due to collisional or collisionless damping mechanisms absorb the mode energy. A schematic of a helicon discharge is illustrated in Figure 10.57. The material processing chamber is located downstream from the plasma source. The plasma potentials in the helicon discharges are typically low, about 15–20 V, similar to ECR-microwave discharges. Important advantages of the helicon discharges with respect to ECR-discharges are related to relatively low values of magnetic field and applied frequency. However, the resonant coupling of the helicon mode to the antenna can lead to a non-smooth variation of the plasma density with source parameters. This effect, known as “the mode jumps” restricts the operating regime for a given design of plasma source.
Analysis of Design Alternatives of Actively Cooled RF Window for MPEX
Published in Fusion Science and Technology, 2021
Joseph B. Tipton, Arnold Lumsdaine, Michael C. Kaufman, Juan Caneses Marin, Jason Cook, Phil Ferguson, Richard Goulding, Dean McGinnis, Juergen Rapp
A steady-state, high-powered helicon source has not been deployed before and is unique to MPEX. The design requirements specific to the helicon are as follows: The helicon antenna is required to produce plasmas with high electron densities in excess of 4 × 1019 m−3 in the source region.The helicon antenna and power supplies shall operate at a fixed frequency of 13.56 MHz.The system shall be configured to provide a coupled power of 175 kW to the MPEX plasma.The helicon system shall operate in steady state to full power.
Ion Fluxes and Neutral Gas Ionization Efficiency of the 100-kW Light-Ion Helicon Plasma Source Concept for the Material Plasma Exposure eXperiment
Published in Fusion Science and Technology, 2019
J. F. Caneses, P. A. Piotrowicz, T. M. Biewer, R. H. Goulding, C. Lau, M. Showers, J. Rapp
Over the years, helicon plasma sources have attracted significant attention because of their high ionization efficiency and ability to produce high-density plasmas with a moderate level of radio-frequency (RF) power (1 to 5 kW). These rf sources use an external antenna to excite whistler waves that propagate across the magnetic field and form eigenmodes in overdense plasmas.1 Recently, light-ion helicon plasma sources have found applications as plasma sources for experiments on plasma-material interaction,2,3 electric thrusters,4,5 and negative ion sources for neutral beam injection.6–8 At present, an intense RF plasma source concept for the Material Plasma Exposure eXperiment (MPEX) is under development at Oak Ridge National Laboratory.2,9,10 An integral part of this concept is the light-ion helicon source used to ionize deuterium gas into a high-density plasma (4 × 1019 to 6), which is subsequently heated with auxiliary RF power sources. Details of the heating systems are described in Ref. 9.