The present invention relates to a method for forming a trench that can remove residual particles in a trench using a metal mask, a method for forming a metal wire, and a method for manufacturing a thin film transistor array panel. The method for forming a trench includes: forming a first insulating layer on a substrate; forming a first metal layer on the first insulating layer; forming an opening by patterning the first metal layer; forming a trench by dry-etching the first insulating layer using the patterned first metal layer as a mask; and wet-etching the substrate. The dry-etching is performed using a main etching gas and a first auxiliary etching gas, and the first auxiliary etching gas includes argon.