Study of TDDB reliability in misaligned via chain structures

The low-k time-dependent dielectric breakdown (TDDB) mechanisms in misaligned via chain structures are studied. The results show that for small and medium inline misalignments, the spacing reduction effect due to via protrusion dominates the variations of failure time distribution, and sqrt-E model can describe the correlation with good accuracy. In the case of larger misalignments, two process related early failure mechanisms have been found. One leakage path is the via bottom discontinuous and hollow area due to via misalignment caused etch-through into bottom dielectrics, and the other mode is related to excess remaining residues generated in the misaligned structure which are difficult to be to completely removed without robust wet clean process. Process optimization approach like the modified multiple-step post etch wet clean has been demonstrated to improve the weakness effectively.