Technology node scaling is driven by the need to increase system performance, but it also leads to a significant power integrity bottleneck, due to the associated back-end-of-line (BEOL) scaling. Power integrity degradation induced by on-chip Power Delivery Network (PDN) IR drop is a result of increased power density and number of metal layers in the BEOL and their resistivity. Meanwhile, signal routing limits the SoC performance improvements due to increased routing congestion and delays. To conquer these issues, we introduce a disruptive technology: wafer backside (BS) connection to realize chip BS PDN (BSPDN) and BS signal routing. We first provide some key wafer processes features that were developed at imec to enable this technology. Further, we show benefits of this technology by demonstrating a large improvement in chip power integrity and performance after applying this technology to BSPDN and BS routing with a sub-2nm technology node design rule. Challenges and outlook of the BS technology are also discussed before conclusion of this paper.
In advanced packages, redistribution layers (RDLs) are extra metal layers for high interconnections among the chips and printed circuit board (PCB). To better utilize the routing resources of RDLs, published works adopted flexible vias such that they can place the vias everywhere. Furthermore, some regions may be blocked for signal integrity protection or manually prerouted nets (such as power/ground nets or feeding lines of antennas) to achieve higher performance. These blocked regions will be treated as obstacles in the routing process. Since the positions of pads, obstacles, and vias can be arbitrary, the structures of RDLs become irregular. The obstacles and irregular structures substantially increase the difficulty of the routing process. This paper proposes a three-stage algorithm: First, the layout is partitioned by a method based on constrained Delaunay triangulation (CDT). Then we present a global routing graph model and generate routing guides for unified-assignment netlists. Finally, a novel tile routing method is developed to obtain detailed routes. Experiment results demonstrate the robustness and effectiveness of our proposed algorithm. 2b1af7f3a8