First, as illustrated in FIG. 7, a photoresist layer PRL may be formed on the polysilicon layer 134 having the first thickness TH1. The photoresist layer PRL may be formed of a photosensitive organic material. In an embodiment, the photoresist layer PRL may include a positive photosensitive organic material in which a portion exposed to light is removed. However, the inventive concepts are not limited thereto, and in another embodiment, the photoresist layer PRL may include a negative photosensitive organic material in which a portion exposed to light is cured.

Then, as illustrated in FIG. 8, the photoresist layer PRL may be patterned to form a first photoresist pattern PR1.

A first mask 310 may be disposed on the photoresist layer PRL, and the photoresist layer PRL may be exposed using the first mask 310. The first mask 310 may include a light transmitting portion 311 and a light blocking portion 312. The light transmitting portion 311 may transmit light, and the light blocking portion 312 may block light. The light blocking portion 312 may overlap the first region R1, the second region R2, and the third region R3 of the polysilicon layer 134, and the light transmitting portion 311 may not overlap the first region R1, the second region R2, and the third region R3 of the polysilicon layer 134.