Mask creation with hierarchy management using cover cells
OwnerEmile Y. Sahouria, Weidong Zhanginventors
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Abstract
A method and apparatus for translating a hierarchical IC layout file into a format that can be used by a mask writer that accepts files having a limited hierarchy. Cover cells of the original IC layout file or a modified file are designated, and the hierarchical file is redefined to include only those designated cover cells. Non-designated cover cells and other geometric data are flattened into the designated cover cells. The hierarchy of the modified file is then redefined to be less than or equal to the hierarchy limit of the mask writing tool.
Claims13
A method of preparing a file that describes an integrated circuit layout for use by a mask writing tool that accepts files having a limited hierarchy, comprising:
- receiving a layout file that defines cells arranged in a hierarchical graph;
- designating a number of cells as cover cells in the hierarchical graph;
- expanding the layout file such that only the designated cover cells remain in the hierarchical graph;
- and
- after designating the cover cells, selectively redefining the hierarchy of the hierarchical graph by expanding and/or copying one or more of the remaining cover cells such that the hierarchical graph has a maximum depth that is less than or equal to the hierarchical limit of the mask writing tool.
A method of selectively redefining the hierarchy of a hierarchical graph to have a depth that is less than or equal to a defined depth limit, comprising:
- receiving a hierarchical graph that includes a number of cells, wherein at least one of the cells has a depth that is greater than the defined depth limit;
- designating one or more of the cells as cover cells for the hierarchical graph;
- redefining the hierarchical graph in terms of the designated cover cells by expanding the nondesignated cells into the designated cover cells;
- and
- analyzing each cover cell in the redefined hierarchical graph to determine if any placement of the cover cell will cause the defined depth limit to be exceeded, and if so, modifying a subgraph of a cell to meet the defined depth limit.
Dependencies are inferred from the claim text.