Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
MAGNETIC RESONANCE ON HEAT TREATMENT CENTRES IN SILICON
J. -M. Spaeth
Fachbereich Physik, Universität Paderborn, 33095 Paderborn,
Germany
Keywords: oxygen, silicon, EPR, ENDOR, impurities
Heat treatment centres, believed to be oxygen aggregate centres,
having "shallow" levels in the gap, are generated by annealing oxygen
containing silicon at 450 degrees C. They can be obtained in a
paramagnetic charge state such that electron paramagnetic resonance
methods can be used to investigate their microscopic structures. In
particular, when the magnetic isotope 17O is diffused into
float-zone (Fz) silicon, one can study the participation of oxygen in
the heat treatment centres. There are two prominent EPR spectra
associated with heat treatment centres; the so-called NL8 spectrum and
the NL10 spectrum. Both spectra differ in their g-values and have
rather narrow lines and show no hyperfine structure. With electron
nuclear double resonance (ENDOR) we investigated NL8 and NL10 centres
in various Fz or Czochralski (Cz) grown silicon single crystals, which
had different acceptor dopings and impurities. Into Fz-Si
17O was diffused. It turned out that in all samples NL8 is
a unique oxygen aggregate defect which does not incorporate any
impurity and which is a double donor (thermal double donor TDD). From
recent ENDOR measurements on 17O nuclei in various stages
of the heat treatment development by annealing up to 200 hours, it was
concluded that the core of the TDDs contained 2 oxygens in a Si
vacancy and a Si interstitial compatible with the model proposed by
Deák et al. The other oxygens are thought to be in interstitial
positions between two Si atoms along <110> directions. Various
different ENDOR spectra were obtained for the NL10 centres depending
on the nature of the compensating acceptors or impurities present in
the crystals. Therefore, it seems that several NL10 defects have
different microscopic structures depending on the impurities
present. Also the energy levels seem different. For example, NL10 in
P-doped silicon is not very shallow. Our results support the
suggestion that the EPR spectrum of NL10 centres is not characteristic
for one specific microscopic structure of an oxygen aggregate
centre. The proposal made in the literature that NL10 defects are
correlated with the TDDs (NL8) must be discarded.
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Last modified: Sat Mar 9 14:50:47 GMT 1996
JG