Effects of substrate materials on self-formation of Ti-rich interface layers in Cu(Ti) alloy films

In our previous studies, thin Ti-rich layers were found to uniformly cover SiO ₂/Si substrate surfaces at the interface with Cu(Ti) alloy films after annealing at elevated temperature. These Ti-rich layers were also found to prevent intermixing between the Cu(Ti) alloy films and the substrate, resulting in a simple barrier formation technique, called "self-formation of the diffusion barrier," which is attractive for fabrication of ultra-large scale integrated (ULSI) interconnect structures. In the present study, to understand the mechanism of self-formation of the Ti-rich barrier layers on the substrate surface, the effects of SiO ₂/Si, SiN/SiO ₂/Si and NaCl substrate materials on the interfacial microstructure were investigated. The microstructures were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) interconnects. It was concluded that the chemical reaction of Ti with the substrate materials was essential for the self-formation of the Ti-rich layers.