AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThA

Paper PS-ThA8
Ion Energy Selection in Expanding Thermal Plasmas by Means of Pulse-Shaped Substrate Bias

Thursday, November 3, 2005, 4:20 pm, Room 304

Session: Plasma Sources and Equipment
Presenter: M.A. Blauw, Eindhoven University of Technology, The Netherlands
Authors: M.A. Blauw, Eindhoven University of Technology, The Netherlands
A.H.M. Smets, Eindhoven University of Technology, The Netherlands
M. Creatore, Eindhoven University of Technology, The Netherlands
M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Pulse-shaped substrate bias was applied to the expanding thermal plasma. In contrast to a sinusoidal RF-waveform, a pulse-shaped RF-waveform can result in a mono-energetic ion flux to the substrate at much lower frequencies.@footnote 1@ A nearly constant substrate potential was observed between two consecutive pulses for argon-hydrogen and argon-oxygen gas mixtures. It implies that the ion flux is nearly mono-energetic because the plasma sheath transit time is much shorter than the pulse period. The ions that reach the substrate during the pulse have energy comparable to the ions at floating potential so that they do not influence the surface processes significantly. All details of the observed substrate potential can be fully described with the equivalent circuit diagram of the substrate bias system. Besides, the ion current density was derived from the linear voltage increase over the coupling capacitor between two consecutive pulses. The absolute ion density was calculated from the measured ion current density using the electron temperature of the bulk plasma. In contrast to a 13.56 MHz sinusoidal substrate bias, which creates a bright glow around the substrate, the pulse-shaped substrate bias does not influence the plasma visibly. The pulse-shaped substrate bias is particularly suitable to improve the properties of several plasma-deposited materials. The reason is that a mild ion bombardment enhances the rearrangement of surface atoms into an ordered structure, whereas highly energetic ions cause permanent damage.@footnote 2@ For example, the pulse-shaped substrate bias could be used to reduce the defect density in amorphous silicon, to increase the compactness of silicon oxide films on polymers, and, to improve the hardness of diamond-like carbon coatings. @FootnoteText@ @footnote 1@S.B. Wang and A.E. Wendt, J. Appl. Phys. 88, 643 +(2000). @footnote 2@J.W. Rabalais et al., Phys. Rev. B 53, 10781 (1996).