A governing parameter, called AFDgen*, which reflects electromigration damage in a polycrystalline line covered with a passivation layer is proposed. The formulation is based on the parameter AFDgen previously introduced in our studies. With the help of AFDgen we can calculate the atomic flux divergence due to electromigration by considering two-dimensional distributions of current density and temperature and also by simply considering the microstructure of polycrystalline lines and bamboo lines. AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline lines and bamboo lines through experimental verification. As the first step in the development of a practical and universal prediction method for electromigration damage, we treated metal lines not covered with a passivation layer. On the other hand, metal lines used in packaged silicon integrated circuits are covered with passivation. Electromigration induces a mechanical stress (atomic density) gradient in such lines. This gradient plays an important role in the mechanism of electromigration damage. The new parameter proposed here, AFDgen*, includes the effect of the atomic density gradient. We develop also an AFDgen*-based method for determination of film characteristics. This method is applied to both covered and uncovered metal lines made of the same Al film. The film characteristics of both line types are obtained experimentally. Based on a discussion about the validity of the obtained characteristic constants, we were finally able to conclude that the AFDgen* parameter and the proposed method for deriving film characteristics are useful.
ASJC Scopus subject areas
- Physics and Astronomy(all)