Improved quality of polycrystalline diamond grown by two-stage growth in microwave plasma chemical vapor deposition

The quality of polycrystalline diamond films grown by chemical vapor deposition is dependent on the growth time, pressure, carbon-to-hydrogen ratio, bias, and nucleation mechanism involved. In this study, reaction gases, methane (CH₄) and hydrogen (H₂), were used to grow polycrystalline diamond on a p-type (111) silicon substrate with a microwave plasma-enhanced chemical vapor deposition system. In addition to the conventional etching, bias-enhanced nucleation, and growth steps, the growth step was further divided into two stages. The first stage (growth I) was carried out at low pressure and the second (growth II) was carried out at high pressure. Results clearly indicate that the use of the growth I stage can considerably improve the quality of the diamond film. In the growth I stage, well-faceted grains with lower contents of graphite and carbide, and fewer defects are obtained. Therefore, the conductivity is drastically decreased by nearly two orders of magnitude and the diamond film exhibits the semi-insulating characteristics of intrinsic diamond. The improvement is caused solely by the addition of the low-pressure growth I stage. Application of bias in the growth I and/or growth II stages can only degrade the synthesized polycrystalline diamond film.