Study of shallow silicon trench etch process using planar inductively coupled plasmas

Silicon shallow trenches applied to the shallow trench isolation of integrated circuits were etched using planar inductively coupled Cl₂ and HBr/Cl₂ 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 Cl₂ and HBr/Cl₂ plasmas were studied using cross-sectional high resolution transmission electron microscopy (HRTEM). The increase of inductive power and bias voltage in Cl₂ and HBr/Cl₂ plasmas increased polysilicon etch rates in general, but reduced the etch selectivity over nitride. In case of Cl₂ 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 Cl₂ 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 Cl₂/N₂ plasmas, and more dense defects in HBr/Cl₂ plasmas possibly due to the penetration of hydrogen in HBr. No defects were found for the trenches etched in pure Cl₂ or Cl₂/O₂ plasmas.