Using a Barrier Layer to Inhibit Ti/Oxide Reaction to Reduce RC Delay and Improve Electromigration in Al-Cu/Ti/W Interconnect for High Power Analog and Mixed Signal Applications

In this paper, we report a novel method to improve aluminum interconnect electromigration performance, reduce metal line sheet resistance (Rs) and reduce via contact resistance (Rc) in a minimum pitch design. We report the effects of bottom redundancy layers on electrical line and via resistance and upstream electromigration performance. We studied 4 metallization stacks: (I) Ti/TiN/AlCu/Ti/TiN, (II) Ti/TiN/Ti/AlCu/Ti/TiN (annealed at 400°C for 20 minutes), (III) a flash process/stack I, (IV) stack III with aluminum deposition temperature of 250°C. Aluminum deposition temperature in stacks I, II, and III are 200°C. Bottom Ti/TiN, AlCu, and Top Ti/TiN layers have the same thickness for all these stacks. Metal line Rs and via contact resistances (Rc) of stack IV are 5% and 10% lower, respectively, than stack I. Stack II metal line sheet resistance is 15% higher than stack I, which is attributed to Al consumption in the TiAl 3 formation during 400°C/20minutes annealing. Electromigration performance is best with stack IV followed by III, II, then I.