Perfect selective and highly anisotropic etching for tungsten polycide (WSix/poly‐Si) structure without sidewall protection is achieved at the electron cyclotron resonance (ECR) position in a newly developed ECR plasma etching system. The etching selectivity ratio of WSix/poly‐Si structure etching to SiO2etching is infinite by using Cl2/SF6/O2gas mixture under 5×10−4Torr. The etching rate is more than 2000 Å/min with no radio frequency bias above selectivity conditions. The addition of a small amount of SF6is efficient for removing tungsten residue. The perfect etching selectivity is caused by low ion energy at the ECR position and the effect of O2gas addition. The high etching rate is achieved by high ion current density at the ECR position. Furthermore, a highly anisotropic etching profile is realized at the substrate temperature of 60 °C.