Phase Aware Proximity Correction for Advanced Masks
In this paper we describe the use of sparse aerial image simulation coupled with process simulation, using the Variable Threshold Resist (VTR) model, to do Optical and Process Proximity Correction (OPC) on Phase Shift Masks (PSM). We describe the OPC of Phase Shift Masks (PSM), including Attenuated PSM, clear field (three or four phases) PSM, and double exposure PSM. We will explain the method used to perform such OPC and show examples of Critical Dimension (CD) control improvements generated from such a technique. Simulations, PSM assignment and model-based OPC corrections are performed with Calibre Workbench, Calibre DRC, Calibre PSMgate and Calibre OPCpro tools from Mentor Graphics. In conclusion we will show that PSM techniques need to be corrected by a phase aware proximity correction tool in order to achieve both pattern fidelity as well as small feature size on the wafer in a production environment.
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