The Effect of Metal Film Topography and Lithography on Grain Size Distributions and on Electromigration Performance

Electromigration performance of a variety of test structures has demonstrated a significant dependence of mean time to failure on topography. In particular, the severity and frequency of steps, both over poly and into and out of contacts, are the primary variables influencing the electromigration results. Materials studies show that the most significant materials parameter that changes at steps is grain size. In fact, it is shown that both lithography dimensions and the presence of topographic variations cause a variation in grain size. The conclusion of the study is that both the topography and lithography of the devices must be comprehended in designing test patterns for the estimation of electromigration performance of actual product devices.