Production of Low Electron-Temperature and High Density Plasma by Using a Grid-Cage Electrode for RF Discharge

Abstract

An original method for producing low electron temperature and high electron density plasma was studied experimentally by using a rectangular grid-cage as a capacitively-coupled powered electrode in a radio frequency (RF) discharge. A rectangular grid-cage electrode was placed on a side wall of a grounded cubic-box chamber of 15x15x15 cm3 in volume. The cubic chamber was situated in a stainless steel vacuum chamber 60 cm in diameter and 100 cm long. An argon plasma was generated by a 40 MHz power source in a pressure range of 2.0 ~ 6.7 Pa. RF power PRF of 5 ~ 60 W was supplied to the grid-cage electrode directly through an impedance matching circuits with a dc blocking capacitor for efficient plasma production. The electron temperature Te and electron density ne were found to be strongly dependent on a mesh size of grid-cage electrodes. If the mesh of the grid-cage was fine, Te  decreased, while ne  increased, compared with those in the case of a coarse grid-cage electrode. By using a fine grid-electrode, Te dropped down to 0.5 eV, while ne reached up to 1.62x1011 cm-3  at the center of the cubic discharge chamber of 15x15x15 cm3under argon pressure of 2.0 Pa and RF power of 60 W. This discharge method easily provides low electron temperature and high density plasmas under the continuous RF discharge.