In recent low-k1 lithography, OPC is required to generate more aggressively fragmented patterns to keep its pattern fidelity on the LSI devices. But over-aggressive OPC might induce a crisis of mask manufacturability. In this paper, using newly defined parameter, DPF (Degree of Pattern Fidelity), quantitative relations between OPC aggressiveness and pattern fidelity are evaluated under several conditions. Next, the concept of MEF is extended for 2D complex patterns using DPF, and is evaluated as a function of OPC aggressiveness. Other mask manufacturability, such as writing time, data volume, and inspection availability would be evaluated as a function of OPC aggressiveness.