Corrosion inhibition of Al metal in microelectronic devices assembled in plastic packages

Aluminum-based metallizations are extensively used as electrical interconnections of integrated power microelectronic devices. It is well known that this metal exposed to moisture is highly sensitive to corrosion due to the chemical interaction of aluminum with water. In this paper we report a study of some Al passivation treatments against moisture corrosion. The proposed treatment can be done on the finished wafer without any damage of other device materials and satisfies the die attach and wire-bonding requirements. It consists of a simple chemical dipping into an organic bath containing a phosphating agent. The passivation behavior of the resulting surfaces has been checked by means of pressure cooker test both on the wafer and power metal oxide semiconductor devices assembled in plastic packages. The surfaces resulting in each process step have been analyzed by means of electron spectroscopy for chemical analysis. The passivated surface is formed of one to two monolayers of ortho- and polyphosphate phases directly grafted onto the alumina surface. The same growth process allows fluorine surface contamination reduction. (C) 2001 The Electrochemical Society.