Application specific integrated circuit with spaced spare logic gate subgroups and method of fabrication

The present invention relates to application specific integrated circuits (ASIC). More particularly, it relates to an ASIC, especially a multiple metal layer ASIC, having easily accessible spare gate wiring. An application specific integrated circuit (ASIC) and method of manufacture. The ASIC includes a substrate layer, at least one metal layer and an operational block. The metal layer is formed above the substrate layer. The operational block is formed in the substrate layer and the metal layer, and is definable by a two-dimensional boundary. The operational block includes a plurality of operational logic gates, a first subgroup of spare logic gates, a second subgroup of spare logic gates, operational wiring and spare gate wiring. The operational logic gates, the first subgroup and the second subgroup are formed on the substrate layer, with the first subgroup being spaced from the second subgroup. The operational wiring is routed into the metal layer and interconnects the operational logic gates to configure the operational block to perform a desired operation. The spare gate wiring is similarly routed into the metal layer. The spare gate wiring is separate from the operational wiring, and connects at least one of the first subgroup logic gates to at least one of the second subgroup logic gates. In a preferred embodiment, a plurality of metal layers are provided, and a spacing between the subgroups dictates that the spare gate wiring, as formed by an automatic routing tool, extends to the outer metal layers where it is accessible by a focused ion beam device.