Suppression of oxidationstackingfault generation by preannealing in N2 atmosphere
Seigô Kishino, Seiichi Isomae, Masao Tamura, and Michiyoshi Maki
Citation: Applied Physics Letters 32, 1 (1978); doi: 10.1063/1.89831
View online: http://dx.doi.org/10.1063/1.89831
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Suppression of oxidation-stacking-fault generation by
preannealing in N2 atmosphere
SeigO Kishino,a) Seiichi Isomae, Masao Tamura, and Michiyoshi Maki
Central Research Laboratory, Hitachi Ltd., Kokubunji, Tokyo 185, Japan
(Received 7 June 1977; accepted for publication 17 October 1977)
Suppression of oxidation-stacking-fault (OSP) generation is studied by x-ray section topography, etching
technique, and transmission electron microscopy (TEM). Microdefects (MO's) are generated in bulk Si
during N2 atmosphere annealing at about l000-1100'C, and their generation is confined to the inner
part of the Si wafer. These MO's grow rapidly during subsequent oxidation. The grown MO's contribute
to stacking faults (SP's) in the inner part of bulk Si. On the contrary, surface OSFs are not introduced
by the subsequent oxidation because no MO's are generated in the surface layer by the preannealing. The
suppression effect of OSP generation by N2 atmosphere preannealing is demonstrated using several
samples.
PACS numbers: 61.70.Ph, 81.6O.-j
Formation of stacking faults during the initial oxidation of a silicon wafer is known to have a detrimental
effect on device performance, For example, the oxidation stacking faults (OSF's) cause filamentary shorts,
microplasma generation sites, and generation -recombination centers. 1 The nucleation sites for OSF's have
been shown to be related to residual mechanical damage,2 local impurity precipitation, 3 and so -called
"swirl" defects. 4
Surface damage can be removed by proper etching
before polishing. However, local impurities and swirl
defects may be either process induced or native to the
original crystal growth. Consequently, removing them
from device wafers has not been a simple matter. Many
efforts have been made 5- 11 to eliminate these OSF's
related to impurity precipitates and grown -in defects.
This paper describes a Simple process of preannealing in a N2 atmosphere whereby OSF nucleation sites are
gettered from the active device side of the wafer. Before introducing the gettering process, the growth be-
havior of microdefects (MO's) in bulk Si is described.
This is because MO's grown during annealing are
thought to be related to the gettering of OSF nucleation
sites.
In this study growth behavior of MO's was investigated
by x-ray section topography using (444) MoKO'I diffraction. 12,13 The detailed structure of MO's was investigated by transmission electron microscopy (TEM) observation. Similar observations have been already carried
out by Tan and Tice, 14 and Maher et al. 15 For observation of OSF's, the etching technique proposed by
Secco 16 was used.
The samples are lO-30-n cm dislocation-free pho-
.• f
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0.70
0.75
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FIG. 1. Arrhenius-type plot of MO size as a functionof anneal
temperature.
f---I
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FIG. 2. X-ray section topographs of MO's using (444) MoKOi j •
(a) and (b) are topographs of specimens after N2 atmosphere
alpresent address: Cooperative Laboratories, VLSI Technology
Research Association, 4-1-1, Miyazaki, Takatsuku,
Kawasaki 213, Japan.
Appl. Phys. Lett. 32( 1), 1 January 1978
annealing at 1042 °C for 3 and 64 h, respectively. (c) is the
topograph of a specimen oxidized at 1100°C after pre annealing
at 1070°C in N 2•
0003-6951/78/3201-0001$00.50
© 1978 American Institute of Physics
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10'
Nt anneal temperature (fOe)
1/00
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1000
11SO
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,
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FIG. 3. TEM photograph of a specimen oxidized at 1100°C
after preannealing at 1000 °C in N2 •
sphorus-doped and boron-doped crucible-grown silicon
wafers. These samples are (100)-oriented 350-J,.lmthick wafers. The oxygen content of the specimen is
9 x 10 11 to 3 X 10 18 cm- 3 as determined by the calibration
procedures of Kaiser et al. 17 Growth behavior of MD's
was investigated using all samples, whereas the gettering experiment of OSF's was carried out on n-type
wafers with a high oxygen content.
To begin with, the dependence of the annealing atmosphere of MD growth was studied by section topography.
As will be reported in a separate paper, 13 MD's are
generated by N2 atmosphere annealing for 6 h at about
1000-1100°C (see the dotted line in Fig. 1). The MD
generation was confined to the inner part of the wafer
as seen in section topographs shown in Figs. 2(a) and
2(b). As the annealing time is prolonged, MD's move
further into. the inner part of the wafer. This is clear
from the comparison of Figs. 2(a) and 2(b), which are
topographs of wafers annealed for 3 and 64 h, respectively. The wafers annealed at 1000-1100°C in N2 for 6
h were subsequently oxidized for 2 h at 1100°C. Then,
each MD was observed again by section topography.
1O'r----------,
10'
I
I
I
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10
FIG. 4. OSF density of each
specimen used for the gettering
experiment.
2
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!
10'
10' L--'----'-----"----'-.....L-L--'----'
1234567
specim~n
no.
Appl. Phys. Lett., Vol. 32, No.1, 1 January 1978
10'0~7;;:0-------:C07=:5-----0"80-'------'
10'/TI'K"}
FIG. 5. OSF density as a function of preannealing temperature
i.n N2 ; preannealing time is 6 h. Each number corresponds to
specimen numbers shown in Fig. 4.
Consequently, MD's generated in each N2 atmosphere
anneal grew rapidly during 2 h oxidation as shown by the
dot-dashed curve in Fig. 1. The activation energy of
MD's (2.2 eV) shown in Fig. 1 differs from that of MD's
generated during oxidation (2.6 eV). 13 This is because
though all samples were oxidized at the same temperature (1100°C), the annealing temperature in a N2 atmosphere was different. The rapid MD growth during the
oxidation was also confined to the inner part of the
wafer as seen in the topograph shown in Fig. 2(c).
After successive annealing in N2 and wet O 2, TEM
observation was carried out using the samples. When
the surface layer to about several J,.lm of a TEM specimen was sampled, no defects were observed. Then,
this surface layer was etched to 50-100 J,.lm. Next, the
specimen was fabricated by thinning the wafer to about
2000 A from the back surface. In this case stacking
faults (SF's) were observed as shown in Fig. 3. These
SF's were never observed in either as -grown wafers or
wafers annealed in the N2 atmosphere. Therefore, it
would seem reasonable to assume that these SF's grew
from MD's generated during the N2 atmosphere annealing. 14.15 This consideration supports the hypothesis that
MD's grow rapidly during oxidation after preannealing
in N2 •
Based on this experiment, the suppression effect of
OSF generation by N2 preannealing was investigated.
The samples used here were n-type wafers with a high
oxygen conterit. These wafers developed OSF's of
rather high denSity by Secco etching after two sequenHal wet oxidations 18 at 1l00°C, where the oxide film
produced during the first oxidation was removed before
the second oxidation.
Before the experiment, each wafer was divided into
four parts (specimens). One part of each wafer was
investigated by Secco etching after the sequential oxidation described above and then OSF's of each wafer were
counted as shown in Fig. 4. The others were annealed
for 6 h in N2 • The annealing temperature of each speciKishino et al.
2
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is under study. The cause is not clear at present.
From the above experimental result, it seems that
nucleation sites for OSF's on the surface are gettered
by N2 atmosphere annealing, if the annealing temperature is below HOOee. At this condition, MD's grow
in the inner part of the wafer in the N2 atmosphere preannealing as has been described. It is also ascertained
that MD's are generated by 950°C annealing in N2 if the
annealing time is sufficiently long, for example, 64 h.
The detailed discussions of the gettering mechanism
will be reported in a separate paper .
IG'
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The authors would like to thank Y. Yatsuda and
S. Aoki for discussions and experimental support.
10'
0
120
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./t(s~c.)
FIG. 6. OSF density as a function of preannealing time in N2•
Annealing temperature is 950°C.
men was varied between 950 and 1150 oe. Then, all
specimens were subjected to the treatment (sequential
oxidation and Secco etching) in order to evaluate the
density of OSF's. Consequently, each specimen developed OSF's with a different density. The OSF density of
each specimen is shown as a function of the annealing
temperature in Fig. 5. The fact that OSF's decrease by
N2 preannealing at 1000-HOOee can be seen in Fig. 5.
It is to be noted that the temperature range is in complete agreement with that of MD growth during annealing in N 2. The N2 atmosphere preannealing at 950 ee
seems to be ineffective in the suppression of OSF
generation from Fig. 5. However, if the annealing time
is prolonged, this temperature annealing also becomes
effective for the suppression, as is clear from Fig. 6.
When the preannealing temperature is over HOOee,
the density of OSF's became higher than that of the
specimen without preannealing in N2 • This phenomenon
lC. N. Varker and K. V. Ravi, in Semiconductor Silicon 1973
(Electrochemical Society, Princeton, N.J., 1973), p. 670.
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(unpublished) •
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Line acoustic waves on cleaved edges8 )
Supriyo Datta, Michael J. Hoskins, and Bill J. Hunsinger
Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
(Received 29 August 1977; accepted for publication 22 October 1977)
The feasibility of fabricating wedges suitable for wave propagation by cleaving LiNbOJ is demonstrated.
This is a simple technique that affords excellent control over the wedge angie. The velocity and field
distribution of line waves along the cleaved edge are predicted well from theory.
PACS numbers: 43.20.+g, 68.25.+j
The existence of nondispersive line acoustic waves 1
a>Work supported by The Joint Services Electronics Program
(U.S. Army, U.S. Navy, and U.S. Air Force) under contract DAAB-07-72-C-0259.
3
Appl. Phys. Lett. 32( 1), 1 January 1978
confined along an edge formed by two stress-free surfaces has been demonstrated theoretically and experimentally. 2-7 However, one of the main problems has
been the difficulty in fab ricating high -q uaUty edges suitable for line wave propagation.
0003-6951/78/3201-0003$00.50
© 1978 American Institute of Physics
3
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