Growth of nanocrystalline diamond films by biased enhanced microwave plasma chemical vapor deposition

Nanocrystalline diamond (NCD) films were grown using biased enhanced growth (BEG) in microwave plasma chemical vapor deposition on mirror polished sil icon substrates at temperatures in the range from 400 to 700 degreesC. The films were characterized by Raman spectroscopy, X-ray diffraction (XRD), Au ger electron spectroscopy and atomic force microscopy (AFM). Hardness of th e films was measured by nano-indentor. Apart from graphitic D and G bands i n the films, the Raman spectra exhibit NCD features near 1140 cm(-1). The r elative intensity of the NCD to graphitic G band in the Raman spectra of th e films is negligible in the films grown at 400 degreesC. It increases with temperature and attains a maximum at 600 degreesC following a sharp decrea se in the films grown at higher temperatures. XRD results also indicate a m aximum concentration of NCD in the film grown at 600 degreesC. Average hard ness of the films increases with temperature from similar to 5 GPa to simil ar to 40 GPa up to 600 degreesC followed by a decrease (similar to 24 GPa) in the film grown at 700 degreesC. Substrate temperature seems to play a cr ucial role in the growth of NCD in BEG processes. An increase in growth tem perature may be responsible for evolving bonded hydrogen and increasing mob ility of carbon atoms. Both factors help in developing NCD in the films gro wn at 500 and 600 degreesC with a combination of subplantation mechanism, d ue to biasing, and a high concentration of H atoms in the gas-phase, typica l of CVD diamond process. At 700 degreesC the implanted carbon atoms may be migrating back to the surface resulting in domination of surface processes in the growth, which in turn should result in increase in graphitic conten t of the films at such a high methane concentration and continuous biasing used in the present study. (C) 2001 Elsevier Science B.V. All rights reserv ed.