A method of selectively activating a chemical process using a DC pulse etcher. A processing chamber includes a substrate therein for chemical processing. The method includes coupling energy into a process gas within the processing chamber so as to produce a plasma containing positive ions. A pulsed DC bias is applied to the substrate, which is positioned on a substrate support within the processing chamber. Periodically, the substrate is biased between first and second bias levels, wherein the first bias level is more negative than the second bias level. When the substrate is biased to the first bias level, mono-energetic positive ions are attracted from plasma toward the substrate, the mono-energetic positive ions being selective so as to enhance a selected chemical etch process.