MECHANICAL-PROPERTIES OF DIAMOND FILMS BY A FILAMENT-ASSISTED CHEMICAL-VAPOR-DEPOSITION

Polycrystalline diamond films are deposited on silicon substrates by a filament assisted chemical vapor deposition method with and without dc bias current onto a substrate. The microstructure and mechanical properties of the films are studied as a function of dc bias current. Relatively large compressive stresses, approximately 100 MPa, are observed in films grown at less than 500 mA bias current and are turned to a tensile stress at a large bias current, 700 mA. The grain size and non-diamond carbon incorporated in the films decreased with increasing bias current, while the Young's modulus and fracture strength increased with increasing bias current. The Young's modulus achieved 860 GPa at maximum, which is close to the value for single crystal diamond, 1,050 GPa. It is concluded that mechanical properties are greatly affected by both grain sizes and non-diamond carbon contents in the film.