Formation and Sustaining Conditions of High-Voltage Ultrashort Pulse Plasma for CVD Processing.

Abstract

Formation and sustaining conditions and the structure of high-voltage ultrashort pulse plasma of CH4 diluted with H2 and Ar gases have been studied for the use of active control of CVD processing. Using square-wave pulsed high voltage with 50∼1000 ns pulse width, voltage-current characteristics, timelag of current rise from that of voltage and emission intensity profiles of the plasma have been investigated. Very high voltages up to several kilovolts can be successfully applied without any plasma nonuniformity on the electrode surface because the pulsed high voltage drops before the transition to arcing. During the pulse period, very large current of more than 102∼103 times as that of usual DC plasma can enter into the plasma field. For the formation of stable pulse plasma, the pulse width should be longer than the timelag, which has been comprehensively expressed by the parameters of pressure, applied voltage and distance between anode and cathode. Through the measurement of potential profiles in the positive column of the plasma, it has been found that the stratified plasma structure can be controlled simply through the parameters of current and pressure.