For 100nm-level patterning using optical lithography, high NA system and various RETs such as PSM, off-axis illumination and OPC are obviously required. In particular, assistant feature (AF)-OPC is indispensable to overcome narrow depth of focus (DOF) caused by iso-dense bias and to compensate for linearity difference under the given OAI condition. Previously we reported the application of AF-OPC in DRAM process with 120nm design rule. The extraction of OPC rule and the feasibility of AF-OPC were successfully confirmed by experimental method in real process. In this paper, more comprehensive and aggressive AF-OPC rule is investigated. The old rule is modified in order to obtain larger common DOF. TO avoid dead zone that means discontinuity between dense line and semi-dense line, we apply a comprehensive rule such as insertion of AF between the neighboring main patterns as many as possible. As a result, the discontinuity of OPC application, which is used with or without AF in the boundary region, is effectively minimized. Also, polygon-shaped AF is used to improve DOF of special main pattern. And then, the mask specification and the behavior of isolated line pattern are predicted in case of very high NA KrF and ArF lithography by simulation result. Considering 100nm design rule, the decrease of common DOF is expected to be severer than now. Finally, the optimum AF-OPC rules such as AF size, space and shape are available and shown in case of very high NA KrF and ArF lithography.