Plasma Impedance: "The end of the line?"

Moore, Jonathan (1999). Plasma Impedance: "The end of the line?". MPhil thesis The Open University.



This report accompanies the research performed during the first three terms of a one-year MPhil program into RP-generated, capacitively-coupled gas discharge plasmas and methods of electrical diagnostics.

Gas discharge plasmas are often used for surface processing in the semiconductor fabrication industry and a discharge’s electrical properties (power and impedance) are often required to be related to its physical and chemical mechanisms. Typical R.F supplies do not incorporate accurate enough power monitors with even fewer indicating impedance. Even so, it is required to measure power and impedance actually at the driven electrode and not prior to a lossy matching network and chamber feed.

The design and calibration of an accurate voltage and current probe are proposed (to be placed at a point between the matching network and the discharge chamber) together with a procedure to fully characterise the transmission line that remains between the probe and electrode.

Finally, a software routine is presented to indicate power and impedance together with distortion of the 2nd and 3rd harmonic, feed efficiency and various equivalent circuits. Results show that the proposed probe is of reasonably high accuracy and that measurements taken of typical plasma discharges relate to theory in the main.

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