An exposure process is described, for defining in a photoresist layer a plurality of first patterns having a first pitch and a second pattern between them that is wider than one first pattern. A first exposure step is conducted to the photoresist layer with a first photomask that has a plurality of the first patterns without a second pattern between them, wherein the first patterns on the first photomask have the first pitch only. A second exposure step is conducted to the photoresist layer with a second photomask that has a third pattern narrower than the second pattern at a position corresponding to the second pattern. The exposure dose of the first or second exposure step alone is not sufficient to define any pattern in the photoresist layer.