Crystalline quality and residual stresses in diamond layers by Raman and x-ray diffraction analyses

A major problem for diamond coating applications is that diamond films tend to exhibit poor adherence on many substrates and typically disbond at thicknesses of the order of a few micrometers principally because of residual stresses. Residual stresses are composed of thermal mismatch stresses and intrinsic tensile film stresses induced during film growth. Diamond films were deposited in a classical tubular microwave plasma reactor from hydrocarbon–hydrogen–oxygen gas mixtures. The stress level was investigated as a function of the gaseous composition (especially oxygen concentration) and deposition temperature (700–900 °C). Thermal stress was directly calculated from Hooke’s law using a biaxial Young’s modulus value of 1230 GPa for polycrystalline diamond. Total diamond film stress was directly determined by the radius of curvature method and by x-ray diffraction using the sin2 ψ method. The microdistorsions and the size of the coherently diffracting domains have been determined from the broadening of the diffraction peak. When coupled also with a Raman study, these investigations allow discussion of the origin of intrinsic stress.