Low-Pressure High-Density Plasma Production for Chemical Vapor Deposition using Directly Heated Cathode Made of Thoriated Tungsten Wire

Abstract

A hot cathode and a mesh anode with a small diameter and a length longer than its diameter are used for deposition on the surface of copper wire. The cathode consists of helical windings of 2% thoriated tungsten wire and is heated to 2000 K by a DC current of 10 A per helical winding. It is found that the plasmas produced in hydrogen gas at pressures lower than 50 mTorr have densities as high as 1011–1012 cm-3, while the electron temperature has two values such as 5–6 eV and 10–12 eV. The electron mean free path is comparable or equal to the diameter of the discharge chamber at the pressure at which the experiments are carried out. It is clarified that the magnetic field induced by the heater current and the electric field locally concentrated near the helical windings are responsible for the mechanisms of the present plasma production.