A semiconductor processing apparatus includes a chamber housing, an electrostatic chuck disposed in the chamber housing, the electrostatic chuck being configured to hold a semiconductor wafer, an edge ring surrounding the electrostatic chuck, the edge ring including a ring electrode disposed within the edge ring, and a ring voltage supply configured to supply a ring voltage to the ring electrode, the ring voltage having a non-sinusoidal periodic waveform, wherein each period of the non-sinusoidal periodic waveform comprises a positive voltage applied during a first time period and a negative voltage applied during a second time period, and wherein the negative voltage has a magnitude that increases during the second time period.