PURPOSE: To form an aluminium pattern having a desired line width, by etching Al in a region capable of performing anisotropic etching by using a gaseous mixture of CHCl3 gas and Cl2 gas as dry etching gas.

CONSTITUTION: In performing the dry etching of Al at a port not coated with a mask layer in such a state that an Al layer is formed on a substrate and the mask layer is applied to the desired part on the Al layer, a geseous mixture prepared by mixing CHCl3 gas and Cl2 gas is used as dry etching gas and the mixing ratio thereof is brought to a region capable of performing anisotropic etching to performing etching. By this method, side etching is prevented even when a mask material excellent in dry etching resistance is used and an aluminum pattern having a desired line width is formed on the substrate.