Void formation by thermal stress concentration at twin interfaces in Cu thin films

A void formation mechanism was investigated in an electroplated copper thin film on Ta/SiO2/Si. Microstructural observation after thermal cycling indi cated that void formation occurred at intersecting points or terminating co rners of annealing twins. The calculated stress distribution was compared w ith experimental results of the void formation tendency. An excellent corre lation was found between void formation sites and stress concentration site s. Electron diffraction analysis revealed that most twin interfaces in Cu t hin films are incoherent {322} planes. The stress concentration drives diff usion along incoherent twin interfaces of {322} and leads to void formation at twin interfaces and corners. (C) 2001 American Institute of Physics.