Interdiffusion reliability and resistivity scaling of intermetallic compounds as advanced interconnect materials

Intermetallic compounds have been proposed as potential interconnect materials for advanced semiconductor devices. This study reports the interdiffusion reliability and resistivity scaling of three low-resistivity intermetallic compounds (Cu2Mg, CuAl2, and NiAl) formed on thermally grown SiO2. Experimental observations and thermodynamic calculations indicated good interdiffusion reliability with CuAl2 and NiAl but not with Cu2Mg. This was due to slow reaction between Al and SiO2 in conjunction with strong chemical bonds of Cu–Al and Ni–Al. As for resistivity scaling, all three intermetallic compounds showed better resistivity scalability than Cu. Resistivity of the thin films was measured and characteristic parameters were obtained by curve fitting using a classical scattering model. First-principles calculations were carried out to determine the electron mean free path and bulk resistivity in order to explain the resistivity scaling. The results showed the importance of having optimum microstructure features, i.e., low-defect-density surface, interface, and grain boundaries in addition to optimum material properties, i.e., a short mean free path and low bulk resistivity. CuAl2 and NiAl appeared to satisfy the interdiffusion and resistivity conditions and be promising candidates to replace Cu interconnections for future devices.