The present disclosure generally relates to apparatuses and methods that control RF amplitude of an edge ring. The apparatuses and methods include an electrode that is coupled to ground through a variable capacitor. The electrode may be ring-shaped and embedded in a substrate support including an electrostatic chuck. The electrode may be positioned beneath the perimeter of a substrate and/or the edge ring. As the plasma sheath drops adjacent the edge ring due to edge ring erosion, the capacitance of the variable capacitor is adjusted in order to affect the RF amplitude near the edge of the substrate. Adjustment of the RF amplitude via the electrode and variable capacitor results in adjustment of the plasma sheath near the substrate perimeter.
