1. A method comprising: receiving a design database corresponding to a mask for IC circuit manufacturing, the design database containing a mask feature; performing a first lithography simulation and evaluation on the design database utilizing a first set of performance indexes; making a modification to the design database, using a computer, based on a result of performing the first lithography simulation and evaluation; performing a second lithography simulation and evaluation on the design database utilizing a second set of performance indexes to verify the modification, wherein the second set of performance indexes is based on the result of performing the first lithography simulation and evaluation; and providing the design database containing the modification to a mask manufacturer for manufacturing the mask utilizing the design database.