Stress in Thin Diamond Films on Various Materials Measured by Microraman Spectroscopy

Abstract

ABSTRACTMicroRaman spectroscopy has been used to determine residual stress in polycrystalline diamond films grown by CVD process in a DC arc plasma from CH4/H2 gas mixtures. A variety of substrate materials, including silica glass, Si, SiC, Mo, Cu, Ni, Fe-Ni alloy, WC-Co and steel, were selected in order to extend as much as possible the range of the substrate thermal expansion coefficients (CTE). Diamond adhesion to catalytically active materials (Ni, Fe, Co) and Cu was improved with a thin buffer layer of CVD tungsten. The observed Raman peak shifts were converted to stress values σmeas in the framework of biaxial stress model. Compressive stress has been found in diamond films at all substrates, except SiO2, which provided a tensile stress up to +2.3 GPa. The maximum compressive stress has been detected for Ni substrate σmeas =-11.4 GPa at room temperature and σmeas =-14.3 GPa at T=78 K. A linear dependence of stress on temperature was found at Ni in the temperature range 78–520 K, in good agreement with prediction of thermal stress model. The splitting of diamond peak to singlet and doublet becomes observable at σ>8–9 GPa. The measured stress correlates in general with calculated thermal stress, increasing with CTE value of respective substrate materials, copper being the only exclusion because of its high plasticity.