Thin film transistor having a copper signal line and method of manufacturing the same

A manufacturing method of an array substrate for a liquid crystal display device, comprising:

• forming a first copper compound layer including nitrogen directly on a substrate;
• forming a first copper layer directly on the first copper compound layer after forming the first copper compound layer including nitrogen;
• forming a gate line and a gate electrode by etching the first copper compound layer and the first copper layer, wherein a top surface of the first copper layer has a narrower width than a top surface of the first copper compound layer and the first copper layer is thicker than the first copper compound layer;
• forming a gate insulating layer on the gate line and the gate electrode;
• forming a forming an active layer on the gate insulating layer over the gate electrode;
• forming an ohmic contact layer the active layer;
• forming a second copper compound layer including nitrogen and directly on the ohmic contact layer;
• forming a second copper layer on the second copper compound layer directly on the ohmic contact layer after forming the second copper compound layer including nitrogen;
• forming a data line, a source electrode, a drain electrode and an island-shaped metal layer by etching the second copper compound layer and the second copper layer on the ohmic contact layer, wherein the data line crosses the gate line, the source and drain electrodes over the gate electrode, and the island-shaped metal layer is disposed directly over the gate line;
• forming a passivation layer on the data line, the source electrode, the drain electrode and the island-shaped metal layer, the passivation layer having a first contact hole exposing the drain electrode and a second contact hole exposing the island-shaped metal layer;
• and
• forming a pixel electrode on the passivation layer, the pixel electrode connected to the drain electrode through the first contact hole and connected to the island-shaped metal layer through the second contact hole,
• wherein the first copper compound layer is disposed between the first copper layer and the substrate to increase adhesion between the first copper layer and the substrate, and the second copper compound layer is disposed between the second copper layer and the ohmic contact layer to prevent a chemical reaction between the second copper layer and the silicon component of the ohmic contact layer.