The present invention includes forming a gate on a transparent substrate. A gate isolation layer is then formed on the gate. An amorphous silicon (a-Si) layer and n+ doped silicon layer are successively formed on the gate isolation layer. Then, the a-Si layer and the n+ doped silicon layer are patterned. A first, a second and a third metal layers are successively formed on the n+ doped silicon layer, thereby forming a multi-metal layer structure. Subsequently, a wet and a dry etching is utilized to etch the multi-metal layer, thereby defining the S/D electrodes. A passivation layer is deposited on the S/D structure.