Pulsed ICP plasma generation and characterization

Abstract

Summary form only given, as follows. Modulated rf power at 13.56 MHz has been applied to a planar coil to generate pulsed, low pressure, inductively coupled argon plasmas (ICP). The modulation is realized by applying a rectangular window function in time to the output of a rf generator, with modulation frequencies between 100 Hz and 30 kHz and duty cycles between 10% and 90%. Current and voltage measurements at the coil are used to measure the peak power. A scanning Langmuir probe and a heterodyne microwave interferometer are used to measure plasma density during the pulse. In addition to these diagnostics, a miniature fiber-optic spectrometer is used to spectrally characterize the light output from the plasma, and a photo multiplier tube with narrow band filters is used to monitor the time dependence of the plasma emission. As expected, much higher peak plasma densities can be produced without damaging the rf window. Also, a reduced surface charging effect has been observed by performing Langmuir probe measurements on the plasma body. Due to the non-linearity of the plasma impedance, excessive rf power reflections and harmonic components of the fundamental rf frequency (13.56 MHz) exist between the ICP antenna and the rf generator that in turn complicate rf power measurements. The results of the experiment and the solutions to the problems encountered in the experiment will be presented.