1. A method for designing an alternating phase shifting mask (altPSM), the mask including a substrate, the method comprising: providing a circuit layout; providing a cutoff layout dimension; identifying a plurality of critical elements of said circuit layout wherein each of said plurality of critical elements has a sub-cutoff dimension less than said cutoff dimension; generating a first phase shape and a second phase shape disposed on opposing sides of each of said sub-cutoff dimensions; providing a first function for defining a phase shape intrusion pair, so that at least said first phase shape and said second phase shape form an intrusion pair; forming a plurality of nets wherein each of said nets comprises at least one phase shape intrusion pair formed in accordance with said first function; coloring phase shapes within each of said nets so that said first phase shape and said second phase shape are assigned opposite phase colors; providing a second function for defining a net intrusion pair. in accordance with a manufacturability constraint; selecting a first net and a second net adjacent to said first net, said first net having a first net edge comprising an outside edge of a first edge phase shape included in said first net, said second net having a second net edge comprising an outside edge of a second edge phase shape included in said second net, wherein said first edge phase shape and said second edge phase shape are assigned a same phase color requiring etching of the substrate and wherein said first net edge and second net edge are adjacent to each other and separated by a background space; forming a third net comprising said first net and said second net in accordance with said second function; and recoloring phase shapes within said third net so that each of said first phase shapes and said second phase shapes are assigned opposite phase colors across each of said critical dimensions and so that said first edge phase shape and said second edge phase shape are assigned opposite phase colors across said background space.