Regensburg 1998 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 24: Poster II
HL 24.20: Poster
Mittwoch, 25. März 1998, 10:30–19:00, A
Conducting AFM for characterization of thin SiO2 — •Alexander Olbrich1,2, Bernd Ebersberger2, Christian Boit2, Johann Vancea1, and Horst Hoffmann1 — 1University of Regensburg, D-93040 Regensburg, Germany — 2Siemens AG, Semiconductor Division HL FA 5, D-81730 Munich, Germany
Reliability of SiO2 has paramount importance for semiconductor
devices. Degradation and early breakdown of MOS structures are
commonly triggered by weak spots like oxide thinning with extensions
on a nanometer scale length. Conducting AFM is used as a non
destructive technique for the electrical characterization of thin
SiO2 on Si by means of Fowler-Nordheim (FN) tunneling through the
oxide. Therefore a constant voltage is applied between the conductive
tip and the Si-substrate and FN currents are measured with a
sensitivity below 50 fA at 400 Hz bandwidth. Mapping of the local FN
currents (typically 0.05 -0.5 A/cm2) simultaneously with the AFM
topography yields information about the local electrical and
structural properties of the oxide.
We investigated device-grade MOS
gate oxides and EEPROM tunneling oxides of various thicknesses ranging
from 3.5 nm to 40 nm after oxidation in order to study the microscopic
mechanism of degradation and breakdown. Furthermore purposely
ill-processed MOS structures were deprocessed to show the ability of
conducting AFM to detect local oxide thinning. Various conducting
coatings for the tips have been investigated with SEM before and after
usage.