Sidelobe formation in photolithographic patterns is suppressed by non-rectangular, non-circular contact openings formed in attenuated phase shift photomasks. The contact openings may be diamond-shaped, star-shaped, cross-shaped, or various other shapes which include multiple vertices. The contact opening shapes may include only straight line segments or they may include rounded segments. The contact openings may be arranged in various relative configurations such as in arrays in which the contact openings are sized and spaced by sub-wavelength dimensions. A method for forming contact openings on a photosensitive film uses the attenuated phase shift photomask to form a contact pattern free of pattern defects. A computer readable medium includes instructions for causing a photomask manufacturing tool to generate the attenuated phase-shift photomask.