Material Characterization of Ti-Cu-Ni-Au(TCNA)-A New Low Cost Thin Film Conductor System

The continued increase in the cost of precious metals such as palladium and gold has stimulated increased interest in the development of lower cost, but equally reliable, substitutes for noble metal thin film conductor systems such as Ti-Pd-Au. This paper discusses a Ti-Cu-Ni-Au (TCNA) substitute which eliminates the use of Pd and reduces the thickness of gold necessary for a .005 ohms per square sheet resistance from 5µm to
\leq
2µm. The reduction in gold thickness can result in considerable cost savings. The TCNA films were deposited by plating, i.e., electron gun evaporation of Ti and Cu followed by the plating of Cu-Ni-Au. The results of TCNA film aging and resistor aging with TCNA at 150°C and 250°C, bondability, adherence, corrosion resistance in air + dry and wet (5% RH) HCl, SO
2
, and NO
2
environments, solderability, and humidity testing (85°C, 85% RH) under bias for encapsulated and unencapsulated TCNA conductors have been found to be comparable to the Ti-Pd-Au system. Nickel in the range of 1 µm if non-porous is a barrier to the diffusion of copper to the gold surface at the temperatures (150-350°C) and times of interest in bilevel Hybrid Integrated Circuit (H lC) fabrication. In addition to its role as a diffusion barrier, nickel also acts as a corrosion inhibitor like Pd in the Ti-Pd-Au system.