Oxide damage during the over etch step of a polycide gate structure is studied. Seven process parameters of the electron cyclotron resonance (ECR) plasma etching system are systematically investigated. These parameters include : rf power, microwave power, main coil and subcoil currents, Cl-2 and O-2 gas flow rate, and pressure. The results show that damage depends strongly on only three parameters : rf power, subcoil current, and O-2 how rate. As a result, a highly anisotropic, damage and poly-Si residue free etch of the polycide gate structure, with a high etch rate, has been achieved. These etch characteristics are critical for manufacturing the next generation of IC products.