Edge roughness reduction

A method for processing a stack with an etch layer below a mask is provided. The mask is treated by flowing a treatment gas, wherein the treatment gas comprises a sputtering gas and a trimming gas, providing pulsed TCP power to create a plasma from the treatment gas, and providing a pulsed bias, wherein the pulsed bias has a same period as the pulsed TCP power, wherein the pulsed TCP power and pulsed bias provide a first state with a first bias above a sputter threshold and a first TCP power, which causes species from the sputtering gas to sputter and redeposit material from the mask, and provide a second state with a second bias below the sputter threshold and a second TCP power, wherein the second TCP power is greater than the first TCP power, which causes species from the trimming gas to chemically trim the mask.