Active Cntrol of Surface Reattion in CVD Orocess by an Ultra-Voltage Pulsed Plasma

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Active control of plasma CVD process focussing on the control of surface reactions has been investigated by use of an ultra-short and high-voltage pulsed discharge plasma. First, formation and sustaining conditions of this kind of pulsed plasma have been clarified. Pulse width should have a value between the lower limit to initiate a discharge and the upper limit to prevent a transition to arcing. Next, using a source gas of methane diluted by hydrogen, which is usually used for a synthesis of diamond, two different types of well-controlled stratified plasma have been realized by changing an applied voltage, pressure and pulse width. One is a transient structure of plasma formation and the other is a quasi-steady structure with a strongly luminous positive column near the anode. Based on the above results, active control of CVD process of diamond formation has been actually performed by superimposing an ultra-short and high-voltage pulsed plasma on the usual DC plasma. It has been found that the unclation density on the substrate surface can be largely enhanced by applying an ultra-short pulsed plasma and that this effect becomes larger for the higher peak voltage, the longer pulse width and lower pressure. This could be due to the increase of supersaturation level of key radical species near the substrate surface through realizing the second type of stratified plasma structure