A radio‐frequency (rf) biased electron cyclotron resonance (ECR) plasma etching technology with efficient ion acceleration in high density and uniform ECR plasma for accurate Al–Si–Cu alloy film etching has been developed. Substrate is located at the ECR position (875 G position) and etching is carried out with 400 kHz rf bias power. This technology achieves high etching rate (more than 5000 Å/min), excellent uniformity (±5%), highly anisotropic and Cu residue‐free etching using only Cl2and Cl2/BCl3gas plasma at a low 100 °C substrate temperature. These characteristics are achieved by the combination of dense and uniform ECR plasma generation and efficient accelerated ion flux at the ECR position by using 400 kHz rf bias.