Diamond films thinner than 30μm were grown on the P-type Si substrate using the hot filament chemical vapor deposition method under $CH_4/H_2$ gas mixture. Residual stress in the films were subsequently measured in air using the laser curvature, the X-ray diffraction (XRD) $sin^2$ ψ, and the Raman peak shift methods. A comparative analysis showed that the residual stress increased from compressive to tensile with the film thickness, but that the maximum or minimum extent of the stresses measured the Raman and XRD peak shift were 3∼4 times larger than those measured by the curvature method. In order to elucidate the disparity, the Raman and XRD peak shifts were calibrated by bending Si beams with diamond films by a known amount, with stress levels known a priori from the beam theory, and Si substrate were measured directly using the sonic resonance method. After the adjustment, the disparities among the stress measurements were significantly reduced with stress ranging between -0.5 GPa to +0.8 GPa, which suggest a need the stress calibration in future studies. This is due to the fact that each measurement method has different characteristics and precise material properties of CVD diamond are not well known. Also, the peak shifting is effected by unknown factors as well as by the residual stress. So, if the residual stress were calculated with an entire amount of peak shifting, they would include some errors when using the Raman and XRD methods. On one side, the results of the curvature method do not reveal true residual stress because of the creep deformation of the Si substrate. Therefore, this method tends to overestimate residual stress, especially at high temperature and long time (a thick film) deposition processes.
The results of each measuring system showed concordant behaviors of the residual stresses with the film thickness. In a thin film, the residual stress exhibited compressive residual stress, because of the thermal stress effect. When increased film thickness, however, the stresses changed to a tensile residual stress due to the intrinsic stress effect. Driving forces of the stress change are grain growth, decrease of the vacancy concentration. Tensile residual stresses were almost saturated, and those showed higher stress values with increased methane flow rate. Consequently, grain boundary, nondiamond, and vacancy acted as a potential source of tensile stress when film thickness increased. Considering the effects of thermal stress and creep deformation of Si substrate, an intrinsic stress were about +0.7 GPa with tensile stress.
