Determination of SF 6 reactive ion etching end point of the SiO 2/Si system by plasma impedance monitoring

Abstract

Plasma impedance monitoring is successfully used to determine the end point of reactive ion etching of a SiO 2 layer lying on a Si substrate in SF 6 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 monitoring parameter found in this work is modelled 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 the Fourier Transform Infrared Spectroscopy (FTIR) measurements and via observation of the plasma colour.