Sub-resolution assist features (SRAF) have been demonstrated to provide significant process window improvement when used in combination with off-axis illumination (OAI) and attenuated phase shifted mask enhanced lithography ("attPSM"). While some through pitch linewidth variations can be reduced through the use of SRAF, the main goal is to improve common process window, leaving the task of linewidth control to conventional optical proximity correction (OPC). OPC in combination with SRAF is also required to address two-dimensional patterning infidelities such as corner rounding and line end shortening, for which SRAF do not provide adequate correction. Finally, OPC will be used as a means of recovering process window that may be lost in layout situations that result in poor SRAF coverage. With an industry wide migration from rules-based OPC to iterative, model-based solutions, the integration of inherently rules based SRAF generation and model-based OPC has to be investigated.