Surface Reconstruction of Aluminum Metallization -- a New Potential Wearout Mechanism

The surface of aluminum metallization on silicon devices can reconstruct with elevated temperature treatments due to the relief of compressive stresses induced by thermal expansion differences between aluminum and silicon. This reconstruction can cause reliability problems because of the development of thin regions in the metal. Also, in multilayer circuits, hillocks can punch through the oxide layer and cause electrical shorts. In this paper the surface reconstruction is categorized into two modes: high temperature--few cycles (device processing) and low temperature--many cycles (device operation). Mechanisms for each of these reconstruction modes are postulated and suggestions for reducing or eliminating this effect are made.