Aluminum and copper interconnects are widely used for microelectronic applications. A problem can arise when interfacial oxides are present. Such oxides can significantly degrade device performance by increasing electrical resistance. This paper describes analyses of interfacial oxide layers found in Al/Ta and Ta/Cu metal stacks. The analyses were performed through transmission electron microscopy (TEM). The data indicated that the interfacial oxides resulted from spontaneous reductions; that is, Al spontaneously reduced Ta2O5 to form Al2O3, while Ta spontaneously reduced Cu oxide to form Ta2O5. (C) 2004 Elsevier B.V. All rights reserved.