Asic- Physical Design

Metal Filling: Whether performed by the designer or by the foundry, metal fill is a mandatory step at advanced nodes to ensure manufacturability and high yield. It involves filling the empty or white spaces near the design with metal polygons to ensure regular planarization of the wafer. Foundry-mandated fill requirements stipulate that the fill density be within specified maximum and minimum parameters. While regular planarization is crucial to prevent over or under polishing of signal routes and active circuitry, metal fill can also negatively affect timing due to increased capacitive coupling to the nearby nets. Thus, the designer must ensure that the metal fill is done without impacting timing-critical nets. In other words, the fill needs to be timing-aware. Timing-awareness is also needed when the engineering change order (ECO) arrives late in the design cycle. The ECOs require the designer to change the layout and fill around the affected area. Thus, the fill method