Formation of diamond films by pulsed discharge plasma chemical vapor deposition.

Abstract

Diamond films were formed by pulsed discharge DC plasma chemical vapor deposition (CVD), wherein the discharge time (Td) and nondischarge time (Tn) during each period of the pulse were changed. A subelectrode at a short distance from the cathode was also laid to provide stable discharge between the cathode and the substrate (anode). The discharge current (Id) between the cathode and the substrate was controlled by the voltage of the pulsed power supply and by the bias voltage to the anode. The crystalline quality of the films deposited on the silicon substrate became superior when Td decreased and Tn increased, although the deposition rate decreased. The optimum values of Td and Tn to deposit high-quality film without decreasing the deposition rate were 0.5 and 2 ms, respectively. Corresponding to these structural changes, the emission intensity of the hydrogen (Ha and Hb) in the plasma increased when the deposition rate increased. The discharge was possible up to high Pg of about 300 torr and the crystalline quality and deposition rate were extremely improved when Pg was increased to about 200 torr The increase of the emission intensity of C2 together with Ha and Hb was observed when Pg increased. The discharge at low Id was also possible and could be deposited on small specimen such as fine tungsten wire of about 100 mm in diameter, which was used for field emission experiments. The field emission from the tungsten wire increased extremely when appropriate diamond film was coated. These results show that the crystalline quality and deposition rate can be controlled over a wide range by this method.