To perform a dry etching processing, without generating residues and without digging an insulator layer partially deep, and to improve the manufacturing yield and the reliability of device.

Among the contained elements of an alloy thin film 2 containing tow or more elements formed on the insulator layer 1, the halide of the element of the highest molar ratio has the property of a gas in a standard state, the percentage content is equal to or higher than 50 mol% of the whole and the percentage content of the element of the second highest molar ratio is equal to or higher than 50 mol% and equal to or less than 40 mol% of the whole. The dry etching processing method of the alloy thin film 2 is provided with the first step of turning a bias power density to 170 mW/cm2 or smaller and performing etching, until the insulator layer 1 appears and the second step of turning the bias power density to 400 mW/cm2 or higher and performing etching, after the first step.