Reaction of Cu-Ti bilayer films in vacuum and hydrogen

Abstract

Thin (0.5‐μm‐thick) films of titanium and copper on titanium were studied in hydrogen and vacuum ambients at temperatures from 350 to 450 °C. The resistivity and stress in the films were measured as a function of time at temperature. Rutherford backscattering spectroscopy and x‐ray analysis were used to identify the compounds formed due to interdiffusion. Resistivity increased significantly in vacuum due to the formation of TiCu and TiCu₃, respectively. The stress generated during formation of TiCu was compressive, while stress generated during the formation of TiCu₃ was tensile. Final stresses in the Ti‐Cu films were tensile. The activation energy for the formation of the compounds was 1.7 eV for TiCu and 2.5 eV for TiCu₃, determined by both stress and resistivity measurements. In hydrogen, no intermetallics formed, due to the diffusion of hydrogen through the copper to form TiH₂ at the Cu‐Ti interface. No resistivity changes were found, but the stress was compressive and remained so. The energy of formation of the hydride using stress for the kinetic parameter was 0.93 eV.