AVS 45th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM1-ThA

Paper EM1-ThA7
Energy Dispersion of the Conduction Band Mass in Ultrathin SiO@sub 2@ Gate Oxides

Thursday, November 5, 1998, 4:00 pm, Room 314/315

Session: Dielectrics
Presenter: R. Ludeke, IBM T.J. Watson Research Center
Authors: R. Ludeke, IBM T.J. Watson Research Center
A. Schenk, Swiss Federal Institute of Technology, Switzerland
Correspondent: Click to Email
The effective conduction band mass m@sub ox@ of a-SiO@sub 2@ has been the subject of extensive studies and considerable controversy, with a defacto value of 0.5m@sub 0@ having been adopted by most researchers.@footnote 1@ The STM based technique of Ballistic Electron Emission Spectroscopy (BEEM) has recently been used to obtain a value of m@sub ox@=(0.63±0.09)m@sub 0@, which was deduced from quantum interference (QI) oscillations in the BEEM current through a 2.8 nm oxide.@footnote 2@ However, the more fundamental issue of the energy dependence of m@sub ox@ has not yet been properly addressed experimentally or theoretically. We report here pronounced QI effects in the BEEM current through 2.2 nm oxides and an assessment of the energy dependence of m@sub ox@(E) obtained from simulations of the transport process. Up to five QI peaks were observed over a kinetic energy range of 2 eV relative to the conduction band minimum (CBM). Peak positions were reproducible to within 0.1 eV for injections at sites previously not exposed to the electron beam. Transmission coefficients (TC) for over-the-barrier injection were calculated by numerically solving the Schrödinger equation, which included both image force effects and an energy dependent m@sub ox@(E). The gradients of m@sub ox@(E) at the energies of the TC maxima were adjusted until a match to the maxima in the data was obtained. With the assumption of a 2.2 nm oxide thickness (measured by ellipsometry, with other measurements in progress), the fits show that m@sub ox@ increases rapidly from 0.60m@sub 0@ near the CBM to 0.86m@sub 0@ 2 eV above the CBM. An expected trend toward m@sub ox@=1m@sub 0@ for larger energies is suggested as well by the results. @FootnoteText@ @footnote 1@A. Schenk and G. Heiser, J. Appl. Phys. 81, 7900 (1997) and references therein. @footnote 2@H.J. Wen, R. Ludeke and A. Schenk, J. Vac. Sci. Technol. B 16, to be published