As shown in FIG. 1, in some embodiments, more than one isolation structure 110 is formed in the substrate 100. In certain embodiments, the isolation structures 110 are trench isolation structures. The formation of the trench isolation structures includes partially covering the substrate 100 with a photoresist pattern (not shown), patterning the substrate 100 to form trenches in the substrate 100 and filling the trenches with an insulator material. For example, the photoresist pattern includes a predetermined pattern with openings corresponding to the predetermined locations of the isolation structures. In some embodiments, as shown in FIG. 1, top surfaces 111 of the isolation structures 110 are substantially leveled with the top surface 100S of the substrate 100. In some embodiments, the top surface 100S of the substrate 100 is substantially leveled with the top surface 111 of the isolation structure 110. In one embodiment, after filling the insulator material in the trenches, a planarization process such as a mechanical grinding process or chemical mechanical polishing process is performed to remove extra insulator material. In some embodiments, the insulator material of the isolation structures 110 includes silicon oxide, silicon nitride, silicon oxynitride, a spin-on dielectric material, or a low-k dielectric material. In one embodiment, the insulator material of the isolation structures 110 may be formed by high-density-plasma chemical vapor deposition (HDP-CVD), sub-atmospheric CVD (SACVD) or by spin-on.