Characterisation of the barrier formation process of self-forming barriers with CuMn, CuTi and CuZr alloys

Abstract

In this work three elements were investigated as Cu alloys for the self-forming barrier approach: Mn, Ti and Zr. Firstly pure alloy films were prepared in the concentration range from 3 to 9at.%. The thin films were analysed with four point probe, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and wafer bow measurements. These methods were used to determine the as-deposited state and the influence of the thermal annealing to the alloy. Additional to this, wafers were prepared with a layer stack of 50nm alloy and 500nm pure copper for electrical measurements. The diffusion behaviour of the alloying element was analysed with energy dispersive X-ray spectroscopy (EDX) and scanning electron microscope (SEM) images. It was shown that Mn and Ti will diffuse through 500nm pure copper film. In contrast for Zr no diffusion was proved. It is forming an intermetallic phase and therefore remains in the alloy film. Transmission electron microscope (TEM) images of the interface show an enrichment of each alloying elements at the silicon oxide interface after the annealing step. This indicates the ability for barrier self formation of all three elements. The barrier effectiveness against Cu diffusion was proved on MIS structures with BTS and TVS measurements.