Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
ON THE IMPACT OF GROWN-IN SILICON OXIDE PRECIPITATE NUCLEI ON
SILICON GATE OXIDE INTEGRITY
J. Vanhellemont
(a),
G. Kissinger (b), K. Kenis (a),
M. Depas (a) and D. Gräf (c)
(a) IMEC, Kapeldreef 75, B-3001 Leuven, BELGIUM
(b) Institute of Semiconductor Physics, D-15204 Frankfurt (Oder),
GERMANY
(c) Wacker-Siltronic GmbH, PO Box 1140, D-84479 Burghausen, GERMANY
Keywords: gate oxide integrity, laser scattering tomography, flow
pattern defects.
Small point defect clusters grown-in during crystal pulling in present
day high quality silicon can have an important impact on gate oxide
integrity (GOI). A pronounced effect of the Czochralski (Cz) crystal
pulling conditions on GOI is indeed observed for gate oxide
thicknesses between 10 and 100 nm. Due to the low density and small
size of these grown-in defects, few tools are available to study their
nature which is therefore not yet well understood. In the present
paper the role of grown-in silicon oxide precipitate nuclei in reduced
GOI is discussed as well as the impact of crystal cooling rate.
Both 150 and 200 mm p-type Cz substrates are studied obtained from
crystals grown with different cooling ramps. In most cases the pulling
rate was above the critical value for stacking fault ring formation,
i.e. yielding crystals which are vacancy-rich. The crystal defect
density before and after gate oxidation is studied with infrared laser
scattering tomography (LST) using a MILSA IRHQ-2 instrument. This
technique reveals in the as-grown wafers defect concentrations in the
range of 1x106 - 2x107 cm-3 in good
agreement with the flow pattern defects (FPD's) observed after
vertical immersion of the wafers in Secco etch for 30 min. The FPD's
are often associated with large vacancy clusters as they are not
observed in slowly pulled crystals which are known to be
self-interstitial rich. Large vacancy clusters are also efficient
scattering centres and therefore can not be differentiated from
SiOx particles by a single LST measurement. It can however
be expected that the growth and anneal kinetics of both types of
scattering particles are strongly different during thermal treatments.
In the present study the evolution of the LST defect density and
size is studied as a function of the gate oxidation conditions and by
performing low temperature thermal pretreatments. LST results are
compared with known oxide precipitate growth kinetics and with the
results of FPD etching before and after the different thermal
treatments. The observed defect densities and sizes are correlated
with gate oxide breakdown characteristics. The impact of crystal
cooling rate and vacancy super-saturation on the defect distribution
and type is discussed.
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Last modified: Mon Feb 19 12:11:06 GMT 1996
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