ABSTRACT
Once designed, digital integrated circuits must be transferred to a physical silicon wafer. This is done by a process of pattern transfer called lithography. The basis for lithography is a set of lithographic masks, which contain the patterns to be transferred to the semiconductor wafer. Physical design of integrated circuits involves the creation of these masks. One mask is used for each pattern transfer step in the wafer fabrication process, so more than 20 masks may be needed to fabricate a BiCMOS wafer. The many mask layers and the sheer complexity of modern VLSI circuits make physical design seem a daunting task. However, using sophisticated computer tools with libraries of devices and circuits makes the problem tractable.
