Plasma CVD of Boron Carbide by Pulsed Secondary Discharge

An improved method of plasma chemical-vapor deposition (CVD) of a thin film of boron carbide has been devised. Boron carbide is useful because it is hard, is electrically insulating, withstands high temperature, and resists chemical attack. Plasma CVD of boron carbide involves the thermal dissociation of feed gases BCl3, CH4, and H2. Prior to the development of the improved method, it had been found that in plasma CVD, the rate of growth is enhanced when the deposition substrate is biased with a positive dc voltage, which gives rise to a secondary discharge. However, the applied dc voltage must be limited (1) so that the current drawn by the secondary discharge does not exceed the capacity of the bias power supply, and/or (2) the current drawn is not so large as to adversely affect the boron carbide deposit.