Improving wireability on nonplanar structures for the next MCM-D generation

Multilevel thin film via interconnect structures can be broadly classified into two categories: 1) filled vias or studs, and 2) unfilled vias. Unfilled via structures demand that the vias be staggered in successive levels during the thin film fabrication, thereby consuming wiring channels. The stud structures, on the other hand, permit the stacking of successive via levels. From an electrical design point of view, stud structures are ideal since they impose the least number of restrictions during the wiring layout. As thin film pitch reduces from 100 μm to 25 μm, it becomes possible to fabricate stud structures without the need of planarization. The paper describes the required conditions for the fabrication of nonplanar stacked via structures, as well as the improved electrical performance, and the reliability evaluation for up to four interconnected metal levels.