A Hierarchical Bit-Map Format for the Representation of IC Mask Data

Abstract

An alternative representation to the usual outline description of geometric entities for IC mask artwork is described. Rather than identifying opaque areas of a mask by individual shape outlines as described by their corners' coordinates, both the opaque and transparent areas of the design are represented by 1's and 0's respectively in a grid pattern or "bit map" of the entire mask plane. A bit-map representation is well suited to many computer design aids which deal with IC layout data. Artwork output programs which require a "MERGE" operation on all shapes of each mask benefit from this data format since it already contains the merged version of each mask's geometric entities. The bit-map format especially promises to increase the operational efficiency of Boolean comparisons of various mask levels as performed by artwork analysis programs for locating design rule errors and for identifying circuit elements directly from the masks. A hierarchical scheme for describing the bit patterns of a mask efficiently is presented which limits the memory requirements of this data format to a size proportional to the usual outline description. Consequently the bit-map representation can be used not only in those computer aids where it supports program functions very well, but also as the central data format for a CAD system.