Pattern forming method, semiconductor device manufacturing method and phase shift photomask having dummy gate patterns

A method for manufacturing a semiconductor device that includes a plurality of gate patterns in parallel with each other within one circuit block provided over a semiconductor substrate, said method comprising:

• preparing a first photomask,
• wherein in said first photomask at least one dummy gate pattern in parallel with said gate patterns is provided when a pitch between said gate patterns is larger than a predetermined maximum pitch, so that pitches between said gate patterns including said dummy gate pattern are less than said predetermined maximum pitch, and are greater than a minimum pitch, which is a minimum distance between said gate patterns, and
• wherein said first photomask comprises a phase shift photomask that comprises first and second openings whose difference in phase is π, said first and second openings alternating between said gate patterns including said dummy gate pattern to form phase edges therein;
• performing a first photolithography process upon a photoresist layer within said circuit block by using said first photomask;
• preparing a second photomask,
• wherein said second photomask comprises a trim photomask that comprises at least one trim opening corresponding to said dummy gate pattern to remove a portion of said photoresist layer corresponding to said dummy gate pattern;
• and
• performing a second photolithography process upon said photoresist layer by using said second photomask.