Diamond films thinner than 10㎛ were grown on the P-type Si substrate using the hot filament chemical vapor deposition method under $CH_4/H_2$ gas mixture. Young's modulus of the films were subsequently measured by sonic resonance method and 4 point bending method. The measurements showed that the Young's modulus of the films increased with film thickness when the film thickness was smaller than 4㎛ and that the Young's modulus of 2% $CH_4$ specimen was larger than that of 3% $CH_4$ specimen. This trend resulted from the densification of the diamond films which was driven by intrinsic stress accumulation with film thickness increased. Driving forces of the intrinsic stress accumulation were grain growth, decrease of the vacancy and nondiamond concentration.
Curvatures at deposition temperature were deduced by subtracting the curvature changes during the cooling process from the measured curvatures at room temperature. Using this in-situ curvatures and the film thickness with the deposition time, an elastic analysis and an elastic/plastic analysis on the diamond films & Si substrate were made. The elastic analysis reasonably explained the stresses of the films when the film thickness was smaller than 10㎛. As films were thicker than 10㎛, the elastic/plastic analysis considering the stress relaxation of the substrate were needed for accurate calculation of the film stresses. In both cases, the average stress in the film tended to saturate around 10㎛ but the intrinsic stress kept increasing during the CVD process. Saturation of the average stress resulted from the balance between the film stress relaxation by bending and the stress build-up by the intrinsic stress development. The monotonic increase of intrinsic stress suggested that microstructural evolution which drove the intrinsic stress, such as vacancy annihilation and grain growth, were under way throughout the whole film growth process.
