Enhanced thermal stability of Cu alloy films by strong interaction between Ni and Zr (or Fe)

Abstract

Low resistivity, phase stability and nonreactivity with surrounding dielectrics are the key to the application of Cu to ultra-large-scale integrated circuits. Here, a stable solid solution cluster model was introduced to design the composition of barrierless Cu–Ni–Zr (or Fe) seed layers. The third elements Fe and Zr were dissolved into Cu via a second element Ni, which is soluble in both Cu and Zr (or Fe). The films were prepared by magnetron sputtering on the single-crystal p-Si (1 0 0) wafers. Since the diffusion characteristics of the alloying elements are different, the effects of the strong interaction between Ni and Zr (or Fe) on the film’s stability and resistivity were studied. The results showed that a proper addition of Zr–Ni (Zr/Ni ⩽ 0.6/12) into Cu could form a large negative lattice distortion, which inhibits Cu–Si interdiffusion and enhances the stability of Cu film. When Fe–Ni was co-added into Cu, the lattice distortion of Cu reached a lower value, 0.0029 Å ⩽ |Δa| ⩽ 0.0046 Å, and the films showed poor stability. Therefore, when the model is applied to the composition design of the films, the strong interaction between the elements and the addition ratio should be taken into consideration.