Study of nanocrystalline diamond synthesis in MPCVD by bias enhanced nucleation and growth

Synthesis of nanocrystalline diamond (NCD) thin films has been investigated using microwave plasma assisted chemical vapor deposition (MPCVD) on mirror-polished and scratched silicon wafers in gas mixtures of methane (CH4) and hydrogen (H2) under substrate bias ranging from 0 to − 250 V. Scanning electron microscopy (SEM), Raman spectroscopy and synchrotron near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the microstructure and chemical bonding of the synthesized films. The results show that substrate stage configuration and substrate holder materials significantly affected diamond primary nucleation. Both increasing the negative bias voltage and methane concentrations decreased the grain size of diamond and increased the content of graphite in the formed films. The combination of increasing bias voltage and methane concentrations can improve the NCD growth more efficiently than single effect alone. The results also show that synchrotron NEXAFS is a powerful tool to study the microstructure and bonding of NCD that cannot be revealed by visible and UV Raman spectroscopy.

► Substrate stage configuration and materials greatly affect diamond nucleation.
► Increasing either substrate bias or CH4 concentrations reduces diamond grain size.
► Increasing both bias and CH4 improves NCD growth more efficiently than either alone.
► NEXAFS can reveal microstructure and bonding information of NCD that Raman cannot.