A method for manufacturing a thin film transistor (TFT) array substrate having enhanced reliability is disclosed. The method includes forming a multilayer structure including at least one first metal layer and a second metal layer made of copper, forming a first mask layer including a first mask area corresponding to a data line and a second mask area corresponding to an electrode pattern to overlap with an active layer, patterning the multilayer structure, thereby forming the data line constituted by the multilayer structure, patterning the second metal layer, thereby forming the electrode pattern constituted by the at least one first metal layer, forming a second mask layer to expose a portion of the electrode pattern corresponding to a channel area of the active layer, patterning the at least one first metal layer, thereby forming source and drain.