A metal wire for a feature of a cell is extended using a grid based on a metal layer of the cell. Each grid element is assigned an "F" designator representing the metal wire being extended, an "E" designator representing blockages to extension of the metal wire, such as metal wires of other features,...http://www.google.de/patents/US6536027?utm_source=gb-gplus-sharePatent US6536027 - Cell pin extensions for integrated circuits
