Enhancement of photoresist ashing by controlling the impedance between bias electrode and ground in an inductively coupled plasma

A variable inductor (an inductor series connected with a variable vacuum capacitor) was connected between the bias electrode and the chamber ground of an inductively coupled plasma, this inductor is used for controlling the impedance between the bias electrode and the chamber ground. The electron temperature, the electron density, and the plasma potential are obtained from the measured electron energy distribution function. When the series resonance between the sheath capacitance and the variable inductor is achieved, the RF current flow through the bias electrode and the plasma potential dramatically increased, and the change in electron temperature and electron density is rare. The increase of plasma potential can be understood by the increase of the RF voltage across the sheath at the bias electrode. As the current flow through the bias electrode and the plasma potential increases, the etching rate of the photoresist on the wafer at the bias electrode is enhanced in the experiment.