Capacitive probes for rf process plasmas

Abstract

Easily built capacitive probes designed for rf potential measurements in low-density reactive process plasmas are shown. The probes use no auxiliary circuitry and are made from easily available materials. They permit accurate measurements of rf fundamental and harmonic amplitudes in the plasma, in sheaths, and on insulating or conducting surfaces in vacuum or plasma environments. Measured values of plasma, sheath, and electrode surface rf potential amplitudes are shown for ∼1010 cm−3 density, unmagnetized and magnetically enhanced 13.56-MHz capacitive discharges in oxygen and nitrogen. Overall probe accuracy is estimated to be about 10% in these plasmas with the spatial resolution as fine as 0.5 mm.