We present a method that utilizes surface topography to control the distribution of grain sizes, single grain segment lengths and polygrain cluster lengths in AI-Cu thin films. Microstructural data for the grain size and segment/cluster length distribution parameters are presented that demonstrate the influence of various topographical features adjacent to conductor lines. Experimental results show the impact of these features on electromigration failure times. Our results demonstrate that the relationship between median failure time and segment length is consistent with the critical threshold length concept for long interconnects containing large numbers of single grain segments and polygrain clusters. These results demonstrate the importance of the segment length and type in controlling electromigration mass transport.