Silicon shallow trenches applied to the shallow trench isolation of integrated circuits were etched using planar inductively coupled Cl-2 and HBr/Cl-2 plasmas and the effects of process parameters such as gas combination, inductive power, and bias voltage on etch rates, selectivities, and etch profiles of silicon trenches were investigated. Also, the physical damages on the trench bottom and sidewall in Cl-2 and HBr/Cl-2 plasmas were studied using cross-sectional high resolution transmission electron microscopy (HRTEM). The increase of inductive power and bias voltage in Cl-2 and HBr/Cl-2 plasmas increased polysilicon etch rates in general, but reduced the etch selectivity over nitride. In case of Cl-2 plasmas, low inductive power and high bias voltage showed an anisotropic trench etch profile, and the addition of oxygen or nitrogen to chlorine also increased the etch anisotropy. The use of pure HBr plasmas showed a positively angled etch profile and the addition of Cl-2 to HBr improved the etch profile more vertically. HRTEM study showed defects formed near the sidewall, bottom, and bottom edge of the silicon trenches etched in Cl-2/N-2 plasmas, and more dense defects in HBr/Cl-2 plasmas possibly due to the penetration of hydrogen in HBr. No defects were found for the trenches etched in pure Cl-2 or Cl-2/O-2 plasmas.