Direct current bias effects in RF induction thermal plasma diamond CVD

Substrate biasing is an emerging technique extensively used in diamond and cBN chemical vapor deposition (CVD) processes. Direct current bias voltages between -400 V and +500 V are here applied to a diamond deposition surface in an RF induction thermal plasma CVD system. This is made possible by introducing a high-impedance filter network, eliminating the time-varying voltage drop across the plasma-substrate junction and suppressing the radio-frequency interference. A traditional limitation of thermal RF systems is thereby overcome. Negative. bias conditions enhance the initial diamond nucleation density. Positive bias improves the diamond quality and augments the film growth rate. A threefold increase in linear growth rate is attained at +500 V as compared to the unbiased case. In conjunction with optical emission spectroscopic diagnostics, the substrate is used as an electrical and thermal probe. Contrary to do arcjet CVD, there is no secondary discharge created in the RF system at positive bias voltage. Also, the role of ion bombardment at negative bias is shown to be of little importance. It is inferred that the predominant mechanism leading here to changes in the diamond deposit under bias conditions is the promotion and suppression of electron emission from the growing diamond.