Electromigration induced evolution of voids in current crowding areas of interconnects

One of the most important issues in the reliability study of IC interconnect lines is electromigration. This phenomenon results in the formation and growth of voids in metal interconnects, which can cause significant fluctuations in interconnect resistance and in the extreme case sever the interconnect line. The electromigration failure occurs, according to different failure criteria by a resistance change of 10-20 %. To accurately simulate interconnect resistance change due to electromigration, tracking the void shape and position is necessary. Simulations of void evolution in linear interconnects began with sharp interface models which showed the insufficiency of these models (D.R. Fridline and A.F. Bower, 1999; M.K. Gungor and D. Maroudas, 1999). Later, prompted by the complexity of void surfaces, diffuse interface models were introduced (R.B.M. Mahadevan, 1999). An alternative diffuse interface model based on the double obstacle potential was proposed by D.N. Bhate et al (2000). However, all these methods require structured underlying meshes and were applied to simple rectangular interconnect geometries. To reach higher mesh adaptability and appropriate refinement quality for the finite element scheme solving diffuse interface models, we used a version of the recursive local mesh refinement algorithm introduced by J. Kossacky (J. Comput. Appl. Math., vol. 55, pp. 275-288, 1994).