Effect of Different Ni Contents on Thermal Stability of Cu(Ni) Alloy Film

Abstract

The effect of doping different contents of Ni on the thermal stability of Cu(Ni) alloy films has been investigated. Cu(Ni) films with different Ni contents were deposited on SiO2/Si substrates by magnetron sputtering, then annealed in vacuum at 350°C to 650°C for 0.5 h. X-ray diffraction analysis and resistance measurements revealed that high-resistance copper silicide was formed after annealing at 450°C for the Cu(Ni, 1.66 at.%) and Cu(Ni, 9.16 at.%) samples. However, no copper silicide was observed for Cu(Ni, 3.59 at.%) even after annealing at 650°C. Transmission electron microscopy provided evidence for a ∼ 25-nm self-formed barrier layer at the Cu/SiO2 interface with Cu(Ni, 3.59 at.%). The failure to form a diffusion barrier for the Cu(Ni, 1.66 at.%) sample resulted from its low Ni doping concentration, which was insufficient to produce such a self-formed layer during annealing. The barrier failure was caused by grain refinement due to the increased Ni content, providing diffusion channels for atom diffusion. The results clearly suggest that addition of an appropriate amount of Ni can improve the thermal stability of Cu(Ni)/SiO2/Si interconnect structure materials.