Time-resolvedcurrent and voltage measurements on a pulsed rf inductively coupledplasma†

Abstract

Time resolved current and voltage measurements have been made on apulsed radio frequency (rf) inductively coupled plasma (ICP) at13.56 MHz in argon. Measurements were made on the rf coil using ahigh-voltage probe, a Rogowski current probe, and a high-performancedigital oscilloscope. Relative phase information was also obtainedso that time resolved rf power measurements could be made. Due tothe inductive nature of the load, measurement of the phase had to bebetter than 0.6 mrad at 13.56 MHz in order that the power measurementswere accurate to 10%. This accuracy in phase measurement was achievedby careful positioning of the probes and by establishing accuratephase calibration procedures. The power was calculated by three methods:discrete Fourier transform, integral of the current voltage product overN periods, and least-squares fits of a sine wave to the measureddata. Time-resolved measurements of the system complex impedance,power loss in the ICP planar coil, and the actual amount of rf powerdelivered to the plasma were made. These measurements give details duringplasma breakdown and show the transition from capacitive toinductive discharge. The results are compared with both time-resolvedplasma emission and time-resolved Langmuir probe measurements.