The impact of inconsistency in assist feature generation on OPC performance

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Sub-Resolution Assist Features (SRAF) are a widely used Resolution Enhancement Technique (RET) used in Optical Lithography. They are used to enhance the printability of the main features. Model Based SRAF (MBSRAF) are now the state of art method for placing SRAF, where numerical simulation is used to predict the optimal SRAF size and location. When a slight change in the environment occurs, very small numerical differences may result, and in some cases for very complex structures, the numerical technique may drive to a different solution, resulting in SRAF solution inconsistency. In addition following the initial placement by MB-SRAF, SRAF Print Avoidance (SPA) models are utilized to modify the SRAF size and placement, to prevent the SRAF printing. This step may change the SRAF solution and consequently cause inconsistency. In this work, a case of SRAF inconsistency is shown and an alternative solution will be presented.