AVS 45th International Symposium
    Thin Films Division Friday Sessions
       Session TF-FrM

Paper TF-FrM1
Annealing of Copper Electrodeposits

Friday, November 6, 1998, 8:20 am, Room 310

Session: Thin Film Deposition from Chemical Precursors
Presenter: C.H. Seah, Nanyang Technological University, Republic of Singapore
Authors: C.H. Seah, Nanyang Technological University, Republic of Singapore
S. Mridha, Nanyang Technological University, Republic of Singapore
L.H. Chan, Chartered Semiconductor Manufacturing Ltd., Republic of Singapore
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Cu is the best metallization candidate to replace Al and its alloys because of its lower resistivity and better electromigration resistance. Significant progress has been made in building multilevel Cu interconnection systems for advanced microelectronics. As a result, it is important to understand how the morphology of the electroplated Cu films and its properties change after annealing at high temperatures. The properties of annealed electroplated Cu films, together with the diffusion barrier performance, have been studied. Electroplating of Cu films was performed onto p-Si with Cu and W seed layers. The barriers film are either TiN, Ta or TaN. The specimens were then annealed at 600 and 700°C in N@sub 2@ atmosphere for grain growth study. The average grain size of the as-plated Cu films was found to be different; larger Cu grains were formed on W seed layer compared to that formed on Cu (600 vs 200 nm). After annealing, all the Cu films recrystallized readily and grain growth occurred. Regardless of the initial grain size of the electroplated Cu films, the final grain size after annealing was found to be similar in both seed materials. The grain sizes were about 1.0 and 1.2 µm after annealing at 600 and 700°C respectively. The driving force for grain growth is the surface energy release from elimination of grain boundaries and thus achieving an equilibrium state. The annealed films produced a layered microstructure, together with the presence of pinholes and cavities. Results show that all the diffusion barriers remained intact after annealing at 600°C. The CVD TiN barrier appeared to fail at 700°C annealing if the film stack contains only 100 Å thick barrier layer. The resistivity of the electroplated Cu films was also found to be reduced from 2.1 microhm-cm to 1.9 microhm-cm after annealing at both temperatures.