High compressive stress in nanocrystalline diamond films grown by microwave plasma chemical vapor deposition

Hard and smooth nanocrystalline diamond (NCD) thin films were deposited on mirror polished silicon substrates by biased enhanced growth in a microwave plasma chemical vapor deposition system. The films were characterized by Raman spectroscopy, X-ray diffraction and atomic force microscopy. Stress in the films was calculated by measuring the radius of curvature of the films on substrates and hardness was measured using a Nanoindenter. Stress in the films increases, first, with decreasing methane concentration in the gas phase while keeping biasing voltage constant, and second, with increasing biasing voltage while keeping the methane concentration constant. Observation of enormous stress (similar to 30 GPa) was possible in the films, which is due to strong adhesion between the films and substrates. To the best of our knowledge, this is the maximum value of stress reported so far in any kind of carbon thin films. It was hypothesized that it is mostly hydrogen content of the films in the methane series and graphitic content of the films in voltage series that are responsible in generating compressive stress in the respective films. The hardness follows almost a reverse trend than stress with the two growth parameters and can be well-defined from the relative concentration of NCD to graphitic content of the films, as estimated from Raman spectroscopy. (C) 2001 Elsevier Science B,V. AII rights reserved.