Two-Stage Bias Enhanced Growth of Nanocrystalline Diamond Films

Biased enhanced growth (BEG) is developed as a process to grow nanocrystalline diamond (NCD) films. In the BEG process the diamond nucleation and growth are obtained in a single stage process. Typical conditions, used in this process, are 5% CH4 in H2 at 30 Torr pressure while heating the substrate in the range of approx. 400 to 700 °C. A negative bias of 200 V is applied and the bias current density to the substrate is controlled. The controlled bias current density gives a different set of combination of conditions (bias current density, bias voltage and microwave power) that results in the growth of NCD films composed of grains in the range of 2-30 nm with surface roughness of 20-30 nm at growth rates varying in the range of 0.5 - 2 micron/hr at 1000 W microwave power.

In the present study, two-stage BEG is reported. In the first stage a bias of 200 V was applied to the substrate for 30 min followed by growth in the second stage at bias voltages varying in the range of 0-320 V. The films were characterized by Raman spectroscopy and atomic force microscopy. Optical properties (thickness and refractive index) of the films were measured by prism-coupling technique using operating wavelengths of 830 and 1300 nm. Hardness of the films was measured by nano-indentor. Hardness increased and roughness decreased with decreasing the bias voltage. Films with average hardness of 75-80 GPa, having stress less than 1 GPa, and rms surface roughness of 15 nm have been obtained. Different regimes of growth were observed, respectively, in the bias range up to 100 V and beyond. A growth mechanism for NCD by BEG process, based on the results, is discussed.