In a method for forming a metal line, a first metal layer and a second metal layer are deposited on a substrate. The first metal layer includes aluminum, and the second metal layer includes molybdenum. A photoresist pattern having a line-shape is formed on the second metal layer. The second metal layer is etched with a chlorine-containing etching gas using the photoresist pattern as a mask. The first metal layer is then etched with a mixture of a chlorine-containing gas and nitrogen gas and/or a mixture of a chlorine-containing gas and argon gas as an etching gas. Impurities such as chlorine ions are removed from the base substrate after etching the first metal layer with a fluorine-containing gas, hydrogen gas, or water vapor. A method for manufacturing a display substrate is disclosed using the method for forming a metal line to form source, drain, and gate electrodes and gate lines.