Mechanistic Study Of Plasma Damage Of Low k Dielectric Surfaces

Bao, J. J.
Shi, H. L.
Liu, J. J.
Huang, H.
Ho, P. S.
Goodner, M. D.
Moinpour, M.
Kloster, G. M.
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Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O-2, N-2/H-2, N-2 and H-2 in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.

Junjing Bao, Hualiang Shi, Junjun Liu, Huai Huang, P. S. Ho, M. D. Goodner, M. Moinpour, and G. M. Kloster. AIP Conference Proceedings 945, 125 (Oct., 2007); doi: 10.1063/1.2815773