Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
OXYGEN PRECIPITATION IN MCZ SILICON: BEHAVIOUR AND DEPENDENCE
ON THE ORIGIN OF RAW MATERIAL AND GROWTH CONDITIONS
T. M. Tkacheva,
G. N. Petrov, K. L. Enisherlova and
N. A. Iasamanov
ELLINA-NT, Research and Production Co., Moscow, RUSSIA
Silicon single crystals grown by Czochralski technique under an
applied combined magnetic field (MCZ) are studied. By changing the
magnetic field during growing process, we can control both the oxygen
concentration and its distribution radially and axially. The
basic research method used is IR spectroscopy according ASTM
standards. The total oxygen concentration is measured using a special
gas analysis method. Total oxygen concentration (TOC) in all kinds of
samples is 20-30% greater than optically active oxygen concentration
(OAOC). The samples grown by conventional Czochralski technique (CZ)
are used as control samples.
Crystal structure is controlled by
X-ray topography using Lang's technique. The very strong and regular
striated contrast is observed in the X-ray pattern of MCZ samples with
large OAOC. As a rule in these samples there is the very high TOC too.
It is shown that the thermal donors generation in MCZ samples is
weaker than in the CZ samples. For comparison MCZ and CZ samples with
approximately equal OAOC are annealed at 450 degrees C for 18
hours. The thermal donors concentration after this annealing in CZ
sample is in 11.5 times more than in MCZ samples.
After heat
treatment at 1050 degrees C for 16 h in MCZ samples an essential
increase of the OAOC is observed. A slow rate of oxygen precipitation
in MCZ samples at the temperature range higher than 850 degrees C is
shown. After the gettering annealing (at 650 degrees C for 16 h plus
1000 degrees C for 4 h with last two steps having been conducted in an
argon atmosphere), a well-defined denuded zone (of ~27 microns wide
for the wafers of group 1 (OAOC is 15.6 ppm) and ~30 wide for the
wafers of group 2 (OAOC is 6 ppm) below the surface is observed. In
the case of wafers of group 2 it is necessary to produce a
preannealing at 450 degrees C for 2 h in air. The section x-ray
topography and etching techniques permitted visualising the formation
of a denuded zone and the presence of defects in the bulk of the
annealed wafers.
CCD-matrix and MOS-transistors made when MCZ-Si
used as substrate material allow one to say that using MCZ-Si it is
possible to increase device crystal yield in comparison with CZ-Si
substrates.
It is clear now that the problem of high purity
silicon single crystals growth includes the search of the suitable raw
material (as a rule, it is natural quartz). The most suitable natural
quartz deposits are the quartz deposits of hydrothermal origin after
metamorphic treatments. More than 20 chemical elements are found in
natural quartz. The analysis of impurity distribution in quartz of
various genotypes show us that the chemical purity of quartz strongly
depends on the P-T conditions and pressure conditions of its
formation. It is shown that the origin of raw material and the growth
conditions are the real reason of further precipitation behaviour of
oxygen in silicon single crystals.
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Last modified: Mon Feb 19 12:11:06 GMT 1996
JG
