Metal etching method

The invention provides a metal etching method, which comprises the following steps of: providing a semiconductor device, forming a metal layer on the surface of the semiconductor device, and forming a grain boundary gap on the surface of the metal layer; photoresist is coated on the surface of the metal layer, exposure and development are carried out, a pattern window is formed in the photoresist, a grain boundary gap is exposed in the pattern window, and photoresist residues exist in the grain boundary gap; oxygen is introduced to form oxygen plasma, and the photoresist on the surface of the semiconductor device, the metal layer in the pattern window and the photoresist residue in the grain boundary gap are pretreated to remove the photoresist residue in the grain boundary gap. According to the method, photoresist residues in the grain boundary gaps are removed through oxygen, so that the lower metal layer can be completely removed without metal residues during etching, the risks of short circuit and electri