THE EFFECTS OF GRAIN-BOUNDARY DIFFUSION ANISOTROPY ON VIA ELECTROMIGRATION FAILURE

Electromigration performance of multilevel interconnect vias is invest igated using a three-dimensional computer model. The model uses the fi nite-element method to obtain self-consistently the temperature and cu rrent density distributions in order to calculate electromigration flu xes. The model includes the polycrystalline grain structure of the tra cks as well as stress-migration and concentration gradient backfluxes. While in single level systems, failure can be analyzed with two-dimen sional models because the fluxes are homogeneous, the inclusion of the third dimension along the track thickness is necessary for multilevel systems. In addition to the effects of hot spots, current crowding, a nd microstructure, it is found that the anisotropy of the grain bounda ry diffusion plays an important role in determining the locations of v oid formation, The microstructural details of the track at. the interf ace with the via, including grain boundary geometry, are very importan t for electromigration studies. (C) 1997 American Institute of Physics .