Investigation of interfacial reactions in thin film couples of aluminum and copper by measurement of low temperature contact resistance

Abstract

Interfacial reactions in bimetallic thin film couples of aluminum and copper were investigated by measurement of contact resistance between 4.2 and 300 K. Results for as-deposited couples indicate that electrical properties, such as resistance and temperature coefficient of resistance, correspond closely to those computed from a simple model involving current flow parallel to the interface. These properties change appreciably after step annealing at elevated temperatures. Results in this case indicate that interfacial reactions commence by nucleation and growth of Al 2Cu along grain boundaries at 145°C, whereas significant solid solution alloying precedes nucleation and growth of intermetallic compounds at 250°C. Homogenization of these couples proceeds, sequentially, by (1) rapid diffusion of aluminum along grain boundaries in copper, (2) rapid diffusion of copper along grain boundaries in aluminum and (3) slower diffusion of each species into grain interiors of the other until a uniform composition, controlled by relative thickness of the constituent films, is achieved. This interpretation of the evolution of contact resistance is entirely consistent with complementary microstructural characterization by optical and transmission electron microscopy and chemical characterization by Auger electron spectroscopy.