Elimination of hillock formation in Al interconnects using Ni or Co

The effect of using bilayer Ni/Al-1%Cu or Co/Al-1%Cu metallization stacks w ith regard to hillock formation is investigated in this study and compared to hillock suppression capabilities of Al-1%Si and Al-1%Cu single layer fil ms and Ti/Al-1%Cu bilayer metallization stacks. Various heat treatments dur ing and immediately after depositions were used to study the resistances of different metallization stack specimens to hillock formation. The densitie s and sizes of hillocks were characterized using scanning electron microsco py and atomic force microscopy, while interfacial reactions between the tra nsition metal layer and Al-1%Cu in the metallization stack were examined us ing glancing angle x-ray diffraction. Resistivities of the bilayer metalliz ation stacks were characterized using conventional four-point probe measure ments. Our studies indicate that metallization processes involving bilayer metallization stacks of nickel and cobalt with Al-1%Cu are more robust comp ared to those involving titanium with Al-1%Cu. The mechanism of hillock for mation is analyzed in light of intermetallic compound formation and stress- strain considerations. (C) 1999 American Institute of Physics. [S0021-8979( 99)08913-6].