A method of fabricating a dual damascene structure is provided comprising forming a photoresist layer on a dielectric layer. A mask including a region that light completely passes over, a region that light partially passes over and a dense region is used for exposure. A development step is carried out to remove the photoresist layer under the region that light completely passes over, to partially remove the photoresist layer under the region that light partially passes over and to leave the photoresist layer under the dense region. The photoresist layer remaining from the forgoing step and the dielectric layer are partially removed to form a via and a trench in the dielectric layer. The via and the trench are filled with metal to form a dual damascene structure.