Selective tungsten on aluminum for improved VLSI interconnects

The selective chemical vapor deposition of tungsten layers over patterned aluminum interconnect is used to fabricate a bilayer metallization, in which all exposed aluminum surfaces are uniformly encapsulated by tungsten. MB DRAM as well as VLSI logic structures fabricated by this method show improved metal step coverage in windows, increased electromigration resistance over standard aluminum alloys, and reduced hillock densities. Applications presented include both single and double level metal VLSI circuits.