A method of etching a hardmask layer formed on a substrate is provided. The method includes supplying an etching gas mixture to a processing region of a processing chamber. A device substrate is disposed in the processing region when the etching gas mixture is supplied to the processing region. The device substrate comprises a substrate and a hardmask layer formed over the substrate. The etching gas mixture comprises a fluorine-containing gas, a silicon-containing gas, and an oxygen-containing gas. The method further includes providing RF power to the etching gas mixture to form a plasma in the processing region. The plasma is configured to etch exposed portions of the hardmask layer.