The aim of the present work was to deposit nano-crystalline dimond films with low surface roughness, high hardness and fracture toughness by microwave PECVD in the ASTeX type reactor from the mixture of hydrogen and methane. The applied microwave power at 2.45 GHz was 900 W, the total pressure ranged from 7.5 to 8.0 kPa, H₂ flow rate was 400 sccm and CH₄ flow rate varied between 8 and 40 sccm, which resulted in CH₄ concentration from 2 to 10%. The substrate used was mirror polished (111) oriented n-doped silicon single crystalline wafer. The substrate temperature and the deposition time varied from 820 to 920 °C and 10 to 35 minutes, respectively. The diamond nucleation process was enhanced using RF (35 W, 13.56 MHz) induced DC self-bias. The time dependence of DC self-bias turned out to be an important characteristic of the growth process. The deposited layers have been analyzed by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry and depth sensing indentation tests.

The analysis of AFM data yielded rms roughness 8.8 nm and autocorrelation length 120 nm. The results of the presented study suggested that the films have a nanocomposite structure and consist of diamond nanocrystals embedded in a amorphous carbon matrix. The films had relatively high hardness (~70 GPa) and elastic modulus (~400 GPa) and exhibited high fracture toughness and excellent adhesion to the substrate.

The work was supported by the Czech Science Foundation (Projects 202/05/0607 and 106/05/0274)

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