Abstract: Using an attenuated phase shifting mask (Att.PSM) with square-section etch window there is the advantage of permitting good resolution and simultaneously increasing the depth of focus and the exposure latitude (the range of energy), improving the lithographic process itself compared to the traditional masks, called binary. The Att.PSM masks introduce the problem of the side lobe effects which is solved with the present invention adopting a polygonal etch window with at least six sides, preferably with an octagonal shape.