Speed limitations due to interconnect time constants in VLSI integrated circuits

The RC time constants for various interconnect materials, including poly-Si, silicides, and Al, are compared with MOSFET speeds at near-micron and submicron design rules. It is found that for design rules below ∼ 2 µm, the rise time of Al interconnects one cm long can exceed the switching delay of state-of-the-art MOSFET circuits. This speed limitation becomes more severe as design rules are reduced further. The effects of the sheet resistance and thickness of gate level interconnects, the thickness of the field oxide, and the dielectric constant of the insulating overlays are quantified.