Infoscience

Thesis

Characterization of a high-density, large-area VHF plasma source

Feasibility Study of Shaped Electrode The objective of this project was a feasibility study of a novel, large-area plasma reactor for thin film production, based on a shaped electrode technique ("lens") to compensate the standing wave non-uniformity.  Cylindrical Test Reactor In the first phase a cylindrical reactor was designed and constructed to show the "proof of principle" of a novel electrode design. The cylindrical geometry of the reactor was chosen in order to allow easier comparison with theory and simulations already performed by the CRPP. The reactor parameters were 100[cm] electrode diameter at an excitation frequency of 67.8[MHz]. First it was shown that uniform electric fields can be obtained (a necessary condition for plasma homogeneity) and subsequently it was demonstrated that the special electrode design can compensate the standing wave effect at VHF.  Rectangular Industrial Reactor The "proof of principle" for the cylindrical shaped electrode paved the way for the rectangular-shaped electrode. A process compatible in-situ optical uniformity measurement system enabled the measurement of the standing wave effect at typical industrial frequencies (13.56[MHz], 27.12[MHz], 40.68[MHz], 67.8[MHz], 100.0[MHz]) in an industrial rectangular, parallel plate electrode reactor design. Operating at 100.0[MHz] required the construction of a triple stub tuner, which is a interesting way of impedance matching at VHF for PECVD. In spite of parasitic edge plasma, the measurements carried out with the rectangular shaped electrode corroborated the conclusions of the cylindrical test reactor experiments.

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