1. A computer-implemented method for creating a metrology target structure design for a reticle layout, comprising: generating one or more initial metrology target structure designs using a set of rules selected based on one or more parameters describing one or more metrology processes that will be used to measure a metrology target structure on a wafer; simulating how one or more initial metrology target structures will be formed on the wafer using input, wherein the input comprises one or more fabrication processes that will be used to form the metrology target structure on the wafer and the one or more initial metrology target structure designs, and wherein said simulating comprises simulating how the one or more initial metrology target structures will be formed on the wafer at different values of one or more parameters of the one or more fabrication processes; and creating the metrology target structure design based on results of said simulating, wherein said creating comprises determining a process window for the one or more initial metrology target structure designs based on the results of said simulating, comparing the process window for the one or more initial metrology target structure designs to a process window for device structures to be formed on the wafer using the one or more fabrication processes, and selecting the metrology target structure design based on the one or more initial metrology target structure designs that have a process window that is larger than the process window for the device structures.