A method for reducing erosion of a mask while etching a feature in a first layer underlying the mask is disclosed. The first layer is disposed on a substrate, with the substrate being positioned on a chuck within in a plasma processing chamber. The method includes flowing an etchant source gas into the plasma processing chamber and forming a plasma from the etchant source gas. The method further includes pulsing an RF power source at a predefined pulse frequency to provide pulsed RF power to the chuck. The pulsed RF power has a first frequency and alternates between a high power cycle and a low power cycle at the pulse frequency. The pulse frequency is selected to be sufficiently low to cause polymer to be deposited on the mask during the low power cycle.