US Patent 11881381 Capacitance measurement without disconnecting from high power circuit

A method and an apparatus of plasma-assisted semiconductor processing is provided. The method comprises: a) providing substrates at each of the multiple stations; b) distributing RF power including a first target frequency to multiple stations to thereby generate a plasma in the stations, wherein the RF power is distributed according to a RF power parameter configured to reduce station to station variations; c) tuning an impedance matching circuit for a first station included in the multiple stations while distributing RF power to the first station by: i) measuring a capacitance of a capacitor in the impedance matching circuit without disconnecting the capacitor from the impedance matching circuit; and ii) adjusting, according to the capacitance measured in (i) and the RF power parameter, a capacitance of the capacitor; and d) performing a semiconductor processing operation on the substrate at each station.