A passivation layer is deposited and a photoresist is formed. The photoresist includes first to third portions with decreased thickness, the second portions located on portions of drain electrodes and data lines and the third portions located on portions of gate lines. A mask for forming the photoresist has rectilinear slits with width and distance of about 0.8-2.0 microns on an area corresponding to the second portions. The passivation layer and an underlying semiconductor layer as well as the photoresist are etched to expose portions of the gate insulating layer under the third portions of the photoresist as well as portions of the passivation layer under the second portions of the photoresist. The exposed portions of the passivation layer and the gate insulating layer are removed to expose the drain electrodes, the gate lines and the data lines as well as portions of the semiconductor layer, which are subsequently removed.