A computer-implemented method of manufacturing an integrated circuit includes placing a plurality of standard cells that define the integrated circuit, selecting a timing critical path from among a plurality of timing paths included in the placed standard cells, and selecting at least one net from among a plurality of nets included in the timing critical path as at least one timing critical net. The method further includes pre-routing the at least one timing critical net with an air-gap layer, routing unselected nets, generating a layout using the pre-routed at least one timing critical net and the routed unselected nets, and manufacturing the integrated circuit based on the layout.