A method including forming an insulating film over first, second, third and fourth regions of a semiconductor substrate; forming a polyimide film on the insulating film; and patterning the polyimide film with a lithography method using a photomask including at least a first region of a first transmittance rate, a second region of a second transmittance rate, a third region having a shading material, and a fourth region, wherein the first, second, third and fourth regions of the photomask correspond to the first, second, third and fourth regions of the semiconductor substrate, respectively.