Mask versus Schematic - an enhanced design-verification flow for first silicon success

Abstract

Layout versus Schematic (LVS) is a commonly used technique employed at the design stage to insure the correctness of physical layout. However, as process technologies continually advance, increasingly complex boolean operations are required to produce the desired on-mask patterns, which are frequently optimized to enhance transistor performance and process margin. Design layout which has been verified by LVS may undergo substantial layout changes when subjected to the mask generation booleans, with potential implications for performance and margin estimation, particularly given the aggressive use of stressors in modern CMOS technologies. Errors in mask generation booleans, which are very difficult to detect by present primitive inspection methods, can easily result in functional failure although the initial LVS predicted success. Therefore, LVS performed at the design stage is no longer an iron-clad guarantee of chip functionality in advanced process technologies. In this paper, we introduce Mask-versus-Schematic (MVS) verification, a novel design verification flow which directly compares the schematic netlist with a netlist extracted after application of all mask generation booleans, in order to insure the correctness of the final mask data just before tapeout. Furthermore, the introduced methodology can be performed using currently available physical verification EDA tools. The experimental results presented here, using examples from some of the industry's most advanced process technology nodes, demonstrate the effectiveness and efficiency of this methodology in detecting errors resulting from mask generation boolean operations.