Novel ion current sensor for real-time,

Abstract

This paper describes a technique for measuring the ion current at a semiconductor wafer while it is being processed in a high-density plasma reactor. The technique does not require the application of any voltage other than the rf bias voltage which is normally applied to wafers, thus avoiding any possible perturbations to the plasma. It relies on external measurements of the radio-frequency (rf) current and voltage at the wafer electrode. There is no need for any probe to be inserted into the plasma. To test the technique, comparisons were made with dc measurements of ion current at a bare aluminum electrode, for argon discharges at 1.33 Pa, ion current densities of 1.3–13 mA/cm2, rf bias frequencies of 0.1–10 MHz, and rf bias voltages from 1 V to 200 V. Additional tests showed that ion current measurements could be obtained by the rf technique in electronegative gases and when electrically insulating layers or wafers were on the electrode.