In a method of forming a reticle and electron beam exposure system, first electron beams are irradiated onto a first region of a blank reticle having a light shielding layer and a photosensitive layer, to form first shot patterns. Second electron beams having a cross-sectional area larger than the first electron beams are irradiated onto a second region of the blank reticle. The photosensitive layer is developed to form first and second mask patterns at the first and second regions, respectively. The light shielding layer is etched off using the first and second mask patterns as an etching mask, thereby forming the mother pattern including a first pattern in the first region and a second pattern in the second region. Accordingly, the enlargement of the second electron beams reduces the scan time for the blank reticle, thereby reducing the process time.