Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
THE INITIAL STAGES OF OXYGEN AGGLOMERATION IN SILICON:
DIMERS, HYDROGEN AND SELF-INTERSTITIALS
R. C. Newman
IRC Semiconductor Materials, The Blackett Laboratory,
Imperial College of Science, Technology and Medicine,
London SW7 2BZ, UK
At high temperatures (T > 600 degrees C), the rate of loss of
Oi atoms from solution in undoped Czochralski Si measured
by IR absorption, together with the measured size and number density
of the precipitates, implies that the Oi atoms migrate with
their normal diffusion coefficient, Doxy.
Self-interstitials (I-atoms) are generated during the precipitation
and Ostwald ripening implies that dissociation of the particles also
occurs. Small precipitate particles have not been identified following
anneals at 500 <= T <= 600 degrees C but there is evidence that
dissociation of particles and the formation of I-atoms still
occurs. For T = 500 degrees C, there is an estimate of only 10-20
oxygen atoms per cluster after anneals if Doxy is assumed
to be normal.
For T <= 500 degrees C, Oi loss measurements indicate that
O2 dimer formation is the predominant rate limiting process
with Doxy close to its normal values and that dissociation effects are
of increasing importance as [Oi]o (grown-in) is
decreased. Thermal donor defects TD(N) with N <= 16 are formed and it
is commonly assumed that they should be identified with clusters of
(Oi)M atoms with M up to approximately
10-20. For this to be feasible it appears necessary that O2
dimers (or related defects, O2I or O2V) diffuse
much more rapidly than isolated Oi atoms and that small
Oi clusters can dissociate with the release of dimers. If
TD centres incorporate a bonded I-atom in the core, there must be
I-atom generation at some unknown stage of Oi
aggregation. Correlated Oi loss and Sum[TD(N)] formation
occurs with Delta[Oi]/Delta(Sum[TD(N)]) approximately equal
to 10.
Doxy can be enhanced by the presence of hydrogen (or D)
impurities and there are corresponding enhancements of
TD-formation. At the higher temperatures (approximately 470 degrees C)
there is partial passivation of TD-centres to form a family of shallow
thermal donors detected by IR electronic absorption. The line
frequencies show shifts when H is replaced by D and these results link
to recent ENDOR data. Available data relating to Oi-I
interactions will be reviewed in relation to their stability and the
possibility of enhanced Oi diffusion.
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Last modified: Mon Feb 19 12:11:09 GMT 1996
JG
