Optimization of OPC runtime using efficient optical simulation

Model-Based Optical Proximity Correction (MBOPC) is now found in nearly all resolution enhancement recipes used in leading technology integrated circuit fabrication facilities. Many masks now have critical dimensions less than the exposure wavelength, which results in light diffraction that distorts the image projected onto the wafer. The industry is relying more and more on MBOPC to compensate for optical effects that are induced during the exposure of these masks. The MBOPC operation is usually the highest computational time contributor in the RET flow. MBOPC procedures include the fragmentation of layout edges longer than a specific value into a number of sub-edges (fragments). The software engine can move and manipulate each fragment to improve the image transferred to the wafer. In the sparse MBOPC approach, each fragment receives one or more optical simulation sites, which is a one-dimensional array of points where light intensity is sampled and calculated. To correctly capture the resist behavior at each simulation site, there must be enough points to ensure extension of the site to a certain distance from the fragment. Adding more points beyond this distance does not add any benefit, but can significantly increase the runtime. This paper presents an automated method that analyzes layouts for different technology nodes that depend on sparse simulations as their MBOPC engine, and reports the optimized number of simulation points that need to be in the simulation site to get the desired accuracy and optimum runtime performance.