FIG. 9 is a schematic top view showing a portion of the structure including the patterned structures 135 and 136 in accordance with some embodiments of the disclosure. In some embodiments, as shown in left and middle portions of FIG. 3, the semiconductor material pattern 136 in the isolating region IR is lightly doped into lightly doped portions 136A. In the left portion of FIG. 3, the X-portions 136X are partially doped to form the lightly doped portions 136A, while the Y-portions 136Y are doped into lightly doped portions 136A as shown in the middle portion of FIG. 3. In one embodiment, the lightly doped portions 136A are formed in the isolating region IR through the same ion implantation process for forming the LDD regions 140 in the active region AR. In certain embodiments, the lightly doped portions 136A are formed in the regions exposed by the photoresist pattern PR1 and the lightly doped portions 136A are formed only in the isolating region IR. In one embodiment, the photoresist pattern PR1 protects the semiconductor material pattern 135 and portions of the semiconductor material pattern 136 from being implanted, so that the lightly doped portions 136A are formed by doping the Y-portions 136Y and parts of the X-portions 136X. Referring to FIG. 3 and FIG. 9, the ring structure of the semiconductor material pattern 136 includes the lightly doped portions 136A (as a ring structure in FIG. 9) and undoped portions 136U of X-portions 136X. In some embodiments, the semiconductor material pattern 135 is not doped in the ion implantation process for forming the LDD regions 140 and the lightly doped portions 136A.