Physical Design Solutions to Tackle FEOL/BEOL Degradation in Gate-level Monolithic 3D ICs

In this paper, we develop physical design tools and methodologies to tackle the inter-tier performance variations caused by low temperature manufacturing in 2-tier gate-level monolithic 3D ICs (M3D). First, we model the top tier front-end-of-line (FEOL) device mobility degradation and its impact on cell delay/power values. Next, we quantify the impact of tungsten interconnect and cost-driven metal layer saving in the back-end-of-line (BEOL) of the bottom tier. These device and interconnect degradation models are used in our new full-chip M3D physical design flow named Derated 2D. This flow overcomes the well-known drawback of the state-of-the-art Shrunk 2D that requires shrinking of layout objects and RC parasitics. Also, Derated 2D performs low-temperature process-aware tier partitioning to effectively keep timing-critical components in the bottom tier. Moreover, Derated 2D conducts timing-driven monolithic inter-tier via (MIV) planning to cope with the resistivity increase in tungsten BEOL. Lastly, Derated 2D offers an effective timing closure solution through a post-route optimization. Experiments based on a foundry-grade 7nm FinFET process design kit (PDK) show that Derated 2D achieves up to 36% performance improvement and 10% energy saving compared with Shrunk 2D. Using a post-route optimization, Derated 2D further improves timing under various FEOL/BEOL degradation settings at a minimum energy overhead.