Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
FORMATION OF THERMAL DONORS IN CZOCHRALSKI GROWN SILICON
UNDER HYDROSTATIC PRESSURE UP TO 1GPa
B. A. Andreev (a),
V. V. Emtsev
(b), A. Misiuk (c) and
K. Schmalz (d)
(a) Institute of Chemistry of High-Purity Substances, Russian
Academy of Sciences, 49 Tropinin St., GSP-445, Nizhnyi
Novgorod, 603600 Russia
(b) Ioffe Physicotechnical Institute, Russian Academy of Sciences,
194021 St. Petersburg, Russia
(c) Institute of Electron Technology, S8 A1. Lotników 32/46,
02-668 Warsaw, Poland
(d) Institute of Semiconductor Physics, Walter-Korsing-Str. 2,
D-15230 Frankfurt (Oder), Germany
Keywords: oxygen, silicon, thermal donors, hydrostatic pressure
Formation processes of thermal donors in Czochralski grown silicon,
especially those formed at 400-500 degrees C, have been studied in
considerable detail. However, their nature and atomic structure are
still a matter of controversy. Additional experimental information is
required to gain a deep insight into this problem. Among various
factors having a strong effect on the formation of thermal donors
(heat treatment regimes, atmospheres, impurities etc), our knowledge
of the impact of mechanical stress is scanty. Wang and Corbett [1]
made an attempt to introduce mechanical stress up to 2 MPa by bending
of samples heat-treated at 450 degrees C. The induced stress exerts
reportedly a remarkable effect on the formation of Thermal Double
Donors (TDD) and the total concentration of thermal donors was twice
as large as in the sample without stress.
In the present work we
discuss in some detail the influence of mechanical stress on the
formation of thermal donors. High-purity Cz-Si samples were subjected
to hydrostatic pressure of 3 MPa and 1.07 GPa during heat treatment at
450 and 600 degrees C. The duration of heat treatment was 10 h for all
samples studied in order to draw a comparison between them and the
data of [1].
Some important results obtained be means of
electrical and optical measurements are as follows:
Heat treatment
of Cz-Si at 450 degrees C under a pressure of 3 MPa leads to a similar
increase in the total concentration of thermal donors as it was
observed in [1]. Increasing pressure results in the concentration of
TD that is by an order-of-magnitude higher than in a reference sample
(without stress). However, it was found that the conductivity in both
cases cannot be a measure of the TDD concentration (as it was believed
in [1]) since the formation of TDD is strongly suppressed. Instead,
donor states deeper than Ec-0.1 eV make their
appearance. Another interesting feature of heat treatment at 450
degrees C under high pressure is that one can observe the formation of
shallow thermal donors at ~Ec-30 meV even for t = 10 h
instead of t > 100 h for samples without stress.
The formation
process of New Donors at 600 degrees C under stress also differs
considerably from those in the reference material. To cite an example,
the latent period of their formation is only a few hours, whereas
without stress it is necessary to anneal samples for t > 20 h until
New Donors appear.
Different factors which may contribute to the
effect of stress (changes in the oxygen diffusivity, generation of
stress-induced defects etc) are discussed.
[1] P. W. Wang and J. W. Corbett, Mat. Res. Soc. Symp. Proc. 59,
Ed. J. C. Mikkelsen Jr, S. J. Pearton, J. W. Corbett, and
S. J. Pennycook, MRS Pittsburgh, Pennsylvania, 1986 pp. 167-172.
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Last modified: Mon Feb 19 17:19:05 GMT 1996
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