A GDS-based Mask Data Preparation FlowData Volume Containment by Hierarchical Data Processing
As the industry enters the development of the 65nm node the pressure on the data path and tapeout flow is growing. Design complexity and increased deployment of resolution enhancement techniques (RET) result in rapidly growing file sizes, which turns what used to be the relatively simple task of mask data preparation into a real bottleneck. This discussion introduces the data preparation scheme in the mask house and analyzes its evolution. Mask data preparation (MDP) has evolved from a flow that only needed to support a single mask lithography tool data format (MEBES) with minimal data alteration steps to one which requires the support of many mask lithography tool data formats and at the same time requires significant data alteration to support the increased precision necessary for today’s advanced masks. However, the MDP flow developed around the MEBES format and it’s derivatives still exists. The design community has migrated towards the use of hierarchical data formats and processes to control file size and processing time. MDP, which from a file size and process complexity point of view is beginning to look more and more like the advanced RET operations performed on the data prior to mask manufacturing, is still standardized on a flat data format that is poorly optimized for a growing number of mask lithography tools. Based on examples it will be shown how this complicates the data handling further. An alternate data preparation flow accommodating the larger files and re-gaining flexibility for turnaround time (TAT) and throughput management is suggested. This flow utilizes the hierarchical GDS-II format as the exchange format for mask data preparation. It complements the existing flow for the most complex designs. The introduction of a hierarchical exchange format enables the transfer of a number of necessary data preparation steps into the hierarchical domain. Data processing strategies are discussed. The paper illustrates the benefit of hierarchical processing based on GDS-II files with experimental data on file size reduction and TAT improvement for direct format conversions vs. re-fracturing as well as other processing steps. The implications for the established data preparation approaches and potential alternatives for the communication between the mask manufacturer and the customer will be discussed. The potential for further enhancements by converting to a hierarchical format that has a more efficient data representation than the commonly used GDS-II format will be discussed and illustrated.
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