Role of Duty Ratio in Diamond Growth by Pulsed DC-Bias Enhanced Hot Filament Chemical Vapour Deposition

Abstract

In this study, the role of the pulse duty ratio was investigatedduring the deposition of diamond films in a hot filament chemicalvapour deposition reactor with a pulsed-dc biased substratepositively relative to the hot filaments. The voltage-currentcharacteristics showed that the discharge current rose with theincrease of biasing voltage, which was modified by the duty ratio.Before deposition, two approaches were adopted for the pre-treatmentof the silicon substrates, respectively, and the substrates werescratched by diamond paste or seeded by diamond powders using theso-called `soft dry polished' technique. Diamond films weredeposited under a fixed discharge power by changing the duty ratios.In the first group with scratched substrates, it was found thatunder a high duty ratio the diamond grew slowly with quite poornucleation, while in the second case a high duty ratio induced ahigh deposition rate and good diamond quality. Reactive hydrocarbonspecies with high energy are essential for the initial nucleationprocess, which is more effectively achieved at a high biasingvoltage in the condition of a low duty ratio. In the film growthprocess, the large discharge current at a high duty ratio representsan increased concentration of electrons and reactive species aswell, promoting the growth of diamond films.