ECR discharges require a magnetic field such that the electrons’ cyclotron frequency is in resonance with the applied microwave frequency, usually 2.45 GHz. Both the large magnetic field of 875G and the microwave waveguide plumbing make these reactors more complicated and expensive than RIE reactors. Unless one uses tricky methods that depend on nonuniform magnetic fields and densities, microwaves cannot penetrate into a plasma if ωp > ω. Aτ 2.45 GHz, that means that the maximum density that can be produced, in principle , is 100 × (2.45/9)2 = 7.4 × 1010 cm−3 [Eq. (A1–9)]. However, this does not hold in the near-field of the launching device, usually a horn antenna or a loop or slot coupler. Densities of order 1012 cm-3 have been produced in ECR reactors because the free-space wavelength of 2.45-GHz radiation is 12.2 cm, and the interior of a 10 cm diam plasma is still within the near-field. This is discussed in more detail later.
KeywordsMicrowave Beach Coupler
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