Use of plasma impedance monitoring for the determination of SF6 reactive ion etch process end points in a SiO2/Si system

It is shown here that plasma impedance monitoring can be used successfully to determine the end point of reactive ion etching of a SiO2 layer lying on a Si substrate in SF6 plasma. The usefulness of this technique is demonstrated using a commercial Plasma Impedance Monitoring (PIM) system. The end point conditions are tested by monitoring changes in the fundamental and the first four harmonic components of the RF current, RF voltage, phase between RF voltage and current, RF discharge power and RF impedance. The best process monitoring parameter found in this work is modeled as a polynomial equation of RF input power, chamber pressure and gas flow rate, from which the end point can be predicted with good precision and easily detected by the PIM. The end point conditions are confirmed by both Fourier Transform Infrared Spectroscopy (FTIR) measurements and via observation of plasma color changes.