PASSIVATION OF CU VIA REFRACTORY-METAL NITRIDATION IN AN AMMONIA AMBIENT

Cu-(27at.% Ti) and Cu-(26at.% Cr) alloys codeposited on silicon dioxide substrates were isochronally annealed for 30 min at 400-700 degrees C in a flowing NH3 ambient. In the Cu-Ti alloy, Ti segregates to the free surface to form a TINx(O) layer and also to the alloy-SiO2 interface to form a Ti5Si3/TiOw bilayer structure. Therefore the resulting structure is an almost completely dealloyed Cu layer located between a surface oxygen-rich Ti nitride and Ti-silicide/Ti-oxide bilayer interfacial structure. In the Cu-Cr alloy system, Cr seems to migrate only to the free surface to form a CrNx passivation layer. A 45 nm Al film was deposited after nitridation, whereupon a second anneal was performed to evaluate these nitride layers as diffusion barriers. The Cr-nitride diffusion barrier is stable up to 600 degrees C compared with Ti nitride that fails at 500 degrees C. The Cu-Cr nitrided samples also showed an overall lower sheet resistance.