Enhancement of ion directionality for vertical profiles and mask damage suppression by biasing the bottom of mask

Because of the importance of fine patterning in semiconductor manufacturing, controlling the directionality of ions to suppress distortions of the etch profile (such as top bowing, necking and bottom not open) is becoming a major challenge. To improve ion directionality by applying a voltage to the bottom of the mask is investigated. A negative voltage is applied to the bottom W layer of the W-SiO2-W structure mask to enhance the directionality of the ions, and the Si etch profiles under the mask in CF4 plasma are obtained by a Field Emission Scanning Electron Microscope (FE-SEM). If negative voltages are applied to the W layer under the mask, the directionality of the ions is enhanced, and a vertical Si etch profiles are observed. In addition, in CF4 plasmas with very low electron temperatures, applying voltage to the lower W layer reduces the lateral etch of W, suppressing undercut and reducing mask damage. This might be due to reduced charge accumulation and mono energetic ion energy distributions.