Study of the ignition behavior of a pulsed dc discharge used for plasma-assisted chemical-vapor deposition

Abstract

An investigation of a pulsed dc discharge used for plasma-assisted chemical-vapor deposition of titanium nitride has been performed in order to understand the nonuniformity of quality and thickness of the deposited films. The experiments have been performed using a gateable image intensifier to study the temporal and spatial light intensity of the discharge. Additionally, a single Langmuir probe has been used to study the temporal evolution of the plasma potential and the charged particle density. The influence of varying parameters like geometry, gas composition, voltage, pressure, duration of the pulses, etc., on the spreading of the plasma has been investigated. Our experiments reveal that in the presence of electronegative species like TiCl4, which is a source gas for the production of titanium nitride, the spreading of the discharge along the substrates is slow, reaching some parts of the reactor with substantial delay. The result is a nonuniform plasma power density in front of the cathode as well as a spatially varying exposure time of the surface to the plasma. These effects are the reason for the inhomogeneity of the deposited films. The experiments revealed that the slow spreading of the discharge is accompanied with low local cathode fall voltages. The problems with the slow spreading of the discharge can be solved by measures which increase the conductivity of the plasma at the beginning of the pulses. The effectiveness of such measures has been studied.