Physical and chemical properties of sputter-depositedTaCxNy films

Abstract

The structural, electronic, optical, and mechanical properties of stoichiometricTaCxNy = 1−x were simulated using an ab initio calculation based on density functional theory(DFT) within the generalized gradient approximation. The calculationsrevealed the theoretical lattice parameter, density of states, refractiveindex, and elastic constants as a function of carbon and nitrogen content.TaCxNy films were subsequently produced on Si wafers using unbalanced magnetron sputtering.The structural, optical, and mechanical properties were measured using x-raydiffraction/transmission electron microscopy, vacuum ultraviolet spectroscopic ellipsometry,and nanoindentation, respectively. The computational and experimental properties werecompared. The lattice parameter, the energy of the 2p bands in the density of states, andthe energy of the interband transitions were found to decrease with increasing C content.No significant changes in the elastic constants were observed as a result of substituting Natoms with C atoms. The hardness and the elastic modulus were in the 40 and 380 GParange, respectively. The experimental Young’s modulus was much smaller than thecomputational one and this discrepancy was attributed to the nanocrystalline nature of thefilms. Also, the elastic constants were found to decrease dramatically for over-stoichiometricfilms.