Production of Large-Diameter Uniform Plasma in mTorr Range Using Microwave Discharge

Abstract

A large-diameter uniform plasma is obtained by microwave discharge without the use of magnetic fields at pressures in the mTorr range. Microwave fields at 2.45 GHz are radiated from a multislotted planar antenna located a short distance above the glass window of a discharge chamber. Overdense plasmas are produced with ± 3-4% uniformity of ion saturation current over 30 cm diameter for wide ranges of microwave power and gas pressure. The discharge can be started up at pressures as low as 0.5 mTorr. The efficient production of overdense plasmas is investigated by measuring microwave field propagation in the system.

Hot-electron flux observation in large-area microwave sustained plasmas

“…[8][9][10] The acceleration of electrons in the enhanced field region should result in a hot electron flux that can be detected in plasma by, e.g., electrostatic probes. Furthermore, a directed flux of electrons capable of ionization should be also observable on the density profiles.…”

Characteristics of large-diameter plasma using a radial-line slot antenna

“…A microwave cannot propagate in a plasma with densities above the cutoff density. 8 The RLSA surface-wave plasma is designed to have the microwave propagate along the quartz-plasma interface in the radial direction. The z-direction evanescent E field with its onset at the quartz-plasma interface accelerates the plasma electrons.…”

Detection of localized hot electrons in low-pressure large-area microwave discharges

“…Plasma inhomogeneity at the interface introduces a locally enhanced electric field ͑component perpendicular to boundary͒ near the region, where the local plasma frequency p equals the applied field frequency . 6 The effect of the enhanced electric field region has been studied both theoretically 7-9 and experimentally [10][11][12][13] and is believed to play an important role in the maintenance of discharges at low gas pressures (Ͻ, where is total electron collision frequency͒. According to the theoretical work by Aliev et al, [7][8][9] in this plasma resonance region, a hot electron tail in the electron energy-distribution function is formed, which sustains the discharge.…”