AVS 45th International Symposium
    Electronic Materials and Processing Division Wednesday Sessions
       Session EM-WeM

Paper EM-WeM6
Chelating Agents for Dry Removal of Metals

Wednesday, November 4, 1998, 10:00 am, Room 316

Session: Fundamentals of Si Cleaning and CMP
Presenter: A. Shah, University of Illinois, Urbana
Authors: A. Shah, University of Illinois, Urbana
L. Ford, University of Illinois, Urbana
L. Nigg, University of Illinois, Urbana
Y. Wang, University of Illinois, Urbana
R. Masel, University of Illinois, Urbana
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We and others have found that various diketonates can be used to remove metals from a variety of surfaces under dry conditions. In this paper we use a variety of surface spectroscopic techniques to characterize the process for the removal of copper, nickel and palladium from various surfaces. We find that there are two regimes with different reactivities, a regime where the metal is (reduced) metallic and a regime where the metal is oxidized. In the oxidized regime, the rate desorption step is volatilization of the metal. In this case, the metal removal rate goes as the volatility of the metal chelate, with hexafluoropentanedione(Hhfac) showing the highest removal rate followed by trifluoropentanedione (Htfac), Hexafluorooctanedione(HFOD), 2,4 pentanedione (Hacac), Tetramethylheptanedione (TMHD). In contrast in the reduced condition, oxidation is rate determining, and the removal rate follows almost the opposite trends. We have also found some unusual effect in the intermediate oxidation conditions. For example, if we work under conditions where Cu1+ forms, we observe much lower removal rates than under conditions where Cu0 or Cu2+ forms. Htfac is the best etchant under minimal oxygen conditions. Finally, we have also discovered that some of the intermediates can polymerize and decompose on the surface, leading to carbon contamination. The main contamination pathway seems to be enhanced by impurities in the source gases. Details are still unclear, but it appears that we need purer source gases than are presently available to do clean etching.