Evolution of nanodiamond seeds during the chemical vapor deposition of diamond on silicon substrates in oxygen-rich plasmas

Methane, oxygen and hydrogen in relative concentrations of 1:0.5:98.5 were employed to deposit diamond films by microwave plasma enhanced chemical vapor deposition on Si(001) substrates seeded with detonation nanodiamonds of 5⋅1010cm−2 density. The interaction between the nanodiamonds and the plasma was investigated as a function of the chamber pressure and the substrate temperature. At 40 Torr and 935 °C, 90% of the seeds were etched, and growth induction occurred with an impractically long time of 23.5 h. Varying the substrate temperature between 827 °C and 935 °C did not lead to faster growth induction. Reducing the chamber pressure to 30 Torr instead resulted in continuous films with induction time as short as 12 min. The induction time and the growth rate exhibited an Arrhenius dependence in the temperature range 769–884 °C with apparent activation energies of 3.7 eV/atom and 0.3 eV/atom, respectively. When at 30 Torr the concentration of the oxygen additive was raised to 1 vol%, the seeds were completely dissolved and no film deposition took place. However, film growth was possible with an oxygen admixture as high as 1.5 vol% on a diamond precursor layer of approximately 55 nm thickness, which was nucleated in an oxygen-free plasma.