A method of forming a tight-pitched pattern. A target pattern including a plurality of first stripe patterns is provided. Each of the first stripe patterns has a first width and a first length. A photomask includes a plurality of second stripe patterns corresponding to the first stripe patterns is provided. Each of the second stripe patterns has a second width and a second length. A first exposure process with the photomask is provided in an exposure system. The first exposure process uses a first light source with a higher resolution that is capable of resolving the second width of each of the second stripe patterns. Finally, a second exposure process with the photo-mask is provided in the exposure system. The second exposure process uses a second light source with a lower resolution that is not adequate to resolve the second width of each of the second stripe patterns.