AVS 45th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS1-TuM

Invited Paper PS1-TuM10
An Overview of Ion-Ion Plasmas for Semiconductor Processing@footnote 1@

Tuesday, November 3, 1998, 11:20 am, Room 314/315

Session: Pulsed Plasmas
Presenter: L.J. Overzet, University of Texas, Dallas
Authors: L.J. Overzet, University of Texas, Dallas
D.J. Economou, University of Houston
J.L. Kleber, University of Texas, Dallas
S.K. Kanakasabapathy, University of Texas, Dallas
B.A. Smith, Texas Instruments Inc.
Correspondent: Click to Email
Negative ions form in almost all discharges used in semiconductor etching and deposition. In addition, the presence of negative ions can impact nearly every aspect of the discharge: from the discharge chemistry and the formation of particulates to the discharge structure and the transfer of energy from the source to electrons. The presence of negative ions forces the question: Can negative ions be used effectively in plasma processing? Recently, several groups have been investigating whether or not negative ions can be used to process semiconductors and the results thus far have been encouraging. We have found that time resolved measurements of pulsed discharges can provide information on how negative ions can be used for surface processing. Negative ions are ordinarily trapped inside the plasma volume, but, pulsed plasmas allow for efficient negative ion extraction during the afterglow period because the negative ion to electron concentration ratio (electronegativity) can increase dramatically. Plasmas with very large electronegativities are often called "ion-ion plasmas." Ion-ion plasmas have such small electron densities, that the sheaths one ordinarily expects to form no longer form in the same fashion and negative ions can more freely reach processing surfaces. This change in the sheath structure during the transition to an ion-ion plasma should be detectable and a proposed "plasma four point probe" for detecting this transition will be presented as well. Finally, high density plasmas can facilitate negative ion extraction because the high densities make the sheaths thin and the plasma source is sometimes positioned far from the processing wafer allowing the electron average energy to be smaller near the wafer. @FootnoteText@ @footnote 1@ This material is based upon work supported by the National Science Foundation under Grant Nos. ECS-9257383 and CTS-9713262 and by the State of Texas Advanced Research Program under Grant No. 009741-043.