According to one embodiment, a substrate processing method includes providing a substrate containing Si raised features, depositing a conformal film on the Si raised features, and performing a spacer etch process that removes horizontal portions of the conformal film while substantially leaving vertical portions of the conformal film to form sidewall spacers on the Si raised features, the performing including a) exposing the substrate to a plasma-excited first process gas consisting of H2 gas and optionally an inert gas, and b) exposing the substrate to a plasma-excited second process gas containing i) NF3, O2, H2, and Ar, ii) NF3, O2, and H2, iii) NF3 and O2, iv) NF3, O2, and Ar, v) NF3 and H2, or vi) NF3, H2, and Ar. The method further includes removing the Si raised features while maintaining the sidewall spacers on the substrate. The removing may be performed using steps a) and b).