1. A method for placing sub-resolution assist features (“SRAF”) with respect to one or more target patterns in a mask layout, comprising: generating an initial SRAF guidance map for the mask layout; placing a first set of one or more SRAF in the mask layout according to the initial SRAF guidance map; generating an updated SRAF guidance map using the first set of one or more SRAF and the one or more target patterns; placing a subsequent set of one or more SRAF in the mask layout according to the updated SRAF guidance map; and repeating the steps of generating an updated SRAF guidance map and placing the subsequent set of one or more SRAF in an iterative process, until a predefined lithographic process window criterion is satisfied.