Study of the dc saddle-field discharge: Application to methane

The electrical characteristics of a dc saddle-field discharge were studied for methane. The dc saddle-field configuration consists of a semitransparent anode sandwiched between two semitransparent cathodes, and an electrically isolated substrate holder plate positioned behind each of the cathodes. In comparison to the standard dc discharge, the dc saddle-field discharge has a lower breakdown voltage and a lower pressure at the minimum breakdown voltage. This is mainly due to the anode semitransparency which increases the ionization efficiency of the discharge. The electric field between the substrate holder and the semitransparent cathode can be adjusted. This is easily achieved by self-biasing through the adjustment of the substrate–cathode resistance. Increasing the substrate–cathode resistance increases the voltage breakdown at low pressure, and the pressure at the minimum breakdown voltage. When the discharge is used for thin film deposition in the abnormal glow regime, the density of ions reaching the substrate can be controlled independently of ion energy. This added degree of control over ion current density and ion energy should prove very useful in the growth of thin films.