Diamond is known as the most promising materials for heat sink and insulator due to its high thermal conductivity and electrical resistivity. Because most of electronic devices need higher performance in smaller size, heat generated in devices and electrical insulators between devices have become serious problems. As a solution for these problems the SOD(Silicon On Diamond) devices have been developed. SOD is a sort of wafer on which devices are printed like SOI (Silicon On Insulator) devices, where diamond is used as insulator materials. Residual stress in diamond thin films is induced by thermal stress from the difference of thermal expansion coefficients, misfit stress between substrate and thin films and intrinsic stress developed by volume changes during the deposition process. The crack in diamond thin films and dislocations in Si wafer were produced by residual stress in diamond thin film. In addition, the bending of Si wafer resulted from the residual stress limits the wafer bonding in SOD process. However, previous studies have focused only on the relation between fabrication process and residual stress without considering the relation between microstructure and residual stress. In this study, the effects of grain size and non-diamond carbon content on residual stress in diamond thin films are investigated. The diamond thin films were deposited by hot filament CVD process. The Si(100) wafers pretreated in ultrasonic condition by fine diamond particles were used as deposition substrate. Deposition temperature was fixed at 1000℃ by adjusting filament temperature to 2100℃ and distance between filament and substrate to 7mm. The deposition time was 10 hours, total pressure was 40 torr and gas flow rate was 100sccm. The methane concentration is controlled from 1.0% to 3.0%. The deposited diamond thin films were annealed at 1150℃ for 1, 3, 5, 30min in order to investigate the change of microstructure and residual stress during annealing treatment. The residual stress was measured by Raman spectroscopy, XRD method and curvature measurement method to compare the measurement methods and find out optimum measurement method. The residual stresses were measured between -700MPa and -900MPa by $sin^2 ψ$ method using diamond (111) XRD peak, from -400MPa to -900MPa by curvature measurement method, and from -400MPa to -600MPa by Raman spectroscopy method using detached diamond thin films as reference peak position. But the texture of diamond thin film made errors in $sin^2 ψ$ method and the plastic flow of Si wafers at 1000℃ was known to make the measured residual stress in curvature measurement method become larger than real values in high stress condition. As a result, the Raman spectroscopy method was found to optimum measurement method of residual stress in diamond thin films. The microstructures of diamond thin films were changed with varying the methane concentration during the hot filament CVD process. The diamond thin films were grown as columnar shapes and the thickness of diamond thin film was not changed with varying the methane concentration. The facet of diamond surface is developed and grain size increases with increasing methane concentration. The non-diamond carbon content decreased with increasing methane concentration. The facet of diamond thin film surface was developed by annealing at 1150℃ in vacuum, but the grain size and non-diamond carbon content increase or decrease abruptly after 1min annealing and then changes slowly. The compressive residual stresses in diamond thin films increased with increasing the methane concentration in CVD process. The stress increased suddenly increased by annealing for 1min and decreased closely to 0. A new model of microstructure of diamond thin films in which the non-diamond carbon was located in diamond grain boundary was suggested to analyze the residual stress. The residual stress in diamond thin films is proportional to the microstructural factor $\frac{1}{sqrt{d(f+1)}}$(d: grain size, f: non-diamond carbon content) by calculation according to the new model. The microstructural factor means the contribution of non-diamond carbon located in grain boundary of diamond thin films to residual stress of diamond thin films. The effects of residual stress on growth orientation of diamond are investigated by measuring the growth orientations from XRD patterns of diamond thin films. The (110) directions in diamond thin films increased with increasing the intrinsic stress, while the (111) direction in diamond thin films increased with decreasing the intrinsic stress.
