Investigation of structural perfection of SiC ingots grown by a sublimation method
Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-2500 ⁰C at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour in the C-axis direction....
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
1999
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| Zitieren: | Investigation of structural perfection of SiC ingots grown by a sublimation method / S.F. Avramenko, V.S. Kiselev, M.Ya. Valakh, V.G. Visotski // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 1. — С. 76-79. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1179372017-05-28T03:04:07Z Investigation of structural perfection of SiC ingots grown by a sublimation method Avramenko, S.F. Kiselev, V.S. Valakh, M.Ya. Visotski, V.G. Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-2500 ⁰C at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour in the C-axis direction. At growth time of about 15 hours we obtained the ingots with 35 mm useful diameter. To determine the polytype composition of SiC ingots the Raman scattering technique was used. The structural defects were investigated by means of reflection and transmission light microscopy and by selective etching. In the best ingots the dislocation density did not exceed 102 cm⁻², the micropipe density - 10-20 cm⁻², and blocks were absent. 1999 Article Investigation of structural perfection of SiC ingots grown by a sublimation method / S.F. Avramenko, V.S. Kiselev, M.Ya. Valakh, V.G. Visotski // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 1. — С. 76-79. — Бібліогр.: 11 назв. — англ. 1560-8034 PACS 81.05. C, D, E, G, H http://dspace.nbuv.gov.ua/handle/123456789/117937 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-2500 ⁰C at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour in the C-axis direction. At growth time of about 15 hours we obtained the ingots with 35 mm useful diameter. To determine the polytype composition of SiC ingots the Raman scattering technique was used. The structural defects were investigated by means of reflection and transmission light microscopy and by selective etching. In the best ingots the dislocation density did not exceed 102 cm⁻², the micropipe density - 10-20 cm⁻², and blocks were absent. |
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Avramenko, S.F. Kiselev, V.S. Valakh, M.Ya. Visotski, V.G. |
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Avramenko, S.F. Kiselev, V.S. Valakh, M.Ya. Visotski, V.G. Investigation of structural perfection of SiC ingots grown by a sublimation method Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Avramenko, S.F. Kiselev, V.S. Valakh, M.Ya. Visotski, V.G. |
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Avramenko, S.F. |
| title |
Investigation of structural perfection of SiC ingots grown by a sublimation method |
| title_short |
Investigation of structural perfection of SiC ingots grown by a sublimation method |
| title_full |
Investigation of structural perfection of SiC ingots grown by a sublimation method |
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Investigation of structural perfection of SiC ingots grown by a sublimation method |
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Investigation of structural perfection of SiC ingots grown by a sublimation method |
| title_sort |
investigation of structural perfection of sic ingots grown by a sublimation method |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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1999 |
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http://dspace.nbuv.gov.ua/handle/123456789/117937 |
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Investigation of structural perfection of SiC ingots grown by a sublimation method / S.F. Avramenko, V.S. Kiselev, M.Ya. Valakh, V.G. Visotski // Semiconductor Physics Quantum Electronics & Optoelectronics. — 1999. — Т. 2, № 1. — С. 76-79. — Бібліогр.: 11 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-07-08T13:02:51Z |
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7 6 © 1999, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 1999. V. 2, N 1. P. 76-79.
1. Introduction
Silicon carbide has a unique combination of electronic
and physical properties for application in various fields
of modern engineering such as high power devices which
operate at high temperature, and devices for microwave
electronics. The modified sublimation Lely method is the
only growth technique providing large bulk SiC crystals
[1-3]. The most serious drawback of this method is low
structural perfection of crystals. Commercially available
6H- and 4H-SiC substrates contain different types of
defects, namely: dislocations, dislocation loops, misori-
ented domains (a mosaic structure), inclusions, blocks
and, especially, micropipes [4]. The crystal defects do not
allow to realize completely advantages of silicon carbide.
This is currently important for progress in the develop-
ment of new semiconductor devices of the next genera-
tion. The concentration of these defects depends mainly
on the growth conditions. Therefore, the aim of the
present paper is to study the influence of the initial stage
growth on the structure of SiC crystals.
PACS 81.05. C, D, E, G, H
Investigation of structural perfection of SiC ingots grown
by a sublimation method
S. F. Avramenko, V. S. Kiselev
Special Design Office of the Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, 252028, Ukraine,
fax: 380(44) 265-19-57, e-mail: kisvs@usa.net
M. Ya. Valakh, V. G. Visotski
Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, 252028, Ukraine,
fax: 380(44) 265-83-42, e-mail: valakh@isp-div6.kiev.ua
Abstract. Monocrystalline SiC ingots were grown by a modified Lely method using 6H-SiC seed
crystals with (0001) base plane. The crystal growth was carried out in the temperature range 2200-
2500 oC at Ar pressure from 2 to 40 mbar. The rate of growth varied between 0.3 and 1.5 mm/hour
in the C-axis direction. At growth time of about 15 hours we obtained the ingots with 35 mm useful
diameter. To determine the polytype composition of SiC ingots the Raman scattering technique
was used. The structural defects were investigated by means of reflection and transmission light
microscopy and by selective etching. In the best ingots the dislocation density did not exceed
102 cm-2, the micropipe density � 10-20 cm-2, and blocks were absent.
Keywords: silicon carbide, modified Lely method, Raman scattering, defects.
Paper received 19.03.99; revised manuscript received 30.03.99; accepted for publication 31.03.99.
2. Equipment and method of growth
We have used the resistively heated industrial furnace
�Redmet-30�. The sublimation vapor transport system
we designed for SiC ingot growth is shown in Fig. 1. The
growth system consists of concentric graphite heater,
crucible made from vacuum-tight graphite with 180 mm
in diameter and 200-mm long, and two heat screens for
thermal insulation made of graphite, rigid carbon foam
and carbon foil. We used a double wall or coaxial ar-
ranged cylinder type crucible [5]. A porous carbon mem-
brane separated the growth cavity in the crucible. At high
temperature the source material diffused through the
membrane to the seed crystal which has lower tempera-
ture in comparison with the source material. As a seed
we used 6H-SiC Lely [5] crystals with (0001) base plane.
The diameters of the seeds lay between 8 and 10 mm.
The seeds were etched in KOH melt (T = 600 oC, t =
= 3-5 min). The orientation of (0001) Si and (0001) C
type plane was determined by this process. The source
material used was the polycrystalline SiC powder of p-
S. F. Avramenko et al.: Investigation of structural perfection of SiC ingots grown ...
77SQO, 2(1), 1999
or n-type conductivity, which was synthesized by us from
Si and C powders. The crystal growth was carried out in
the temperature range 2200-2500 oC and at the Ar pres-
sure ranging from 2 to 40 mbar. The average rate growth
varied from 0.3 to 1.5 mm/hour in the C-axis direction.
When the growth time was as long as 15 hours we ob-
tained the ingots with 35 mm useful diameter.
3. Results and discussion
To determine SiC ingots polytype composition we used
the Raman scattering technique [6-9]. Structural defects
were investigated by means of reflection and transmis-
sion light microscopy. In order to study crystal parame-
ters, ingots were cut into plates in two directions: paral-
lel and perpendicular to the C axis. The thickness of the
plates varied from 0.5 to 1.0 mm. The facets of these plates
were the crystallographic planes {0001}, {1120}, {1100}.
It enabled to study not only the basis plane {0001}, par-
allel to the surface of the seed, but also facets {1120}
and {1100}. The plates were polished with diamond
pastes and etched in KOH melt. Thermoelectric power
measurements were used to determine the conductivity
type. The etching in KOH melt is polishing for a plane
{0001} C and selective for a plane {0001} Si. In the lat-
ter case, the etch pits are seen on the surface. Their shape
depends on the tilt of dislocations and on the type of
defects. The shape of dislocation etch pits is the inverted
hexagonal pyramid, and the etch pits for tilted disloca-
tions are the deformed hexagonal pyramid. The defor-
mation is dependent on the angle between the disloca-
tion and {0001} Si plane. The etch pits of closed disloca-
tion loops have the same shape but are smaller and of-
ten situated in pairs. Other microdefects and the inclu-
sions of other phases have etch pits with flat bottom (in-
verted truncated pyramid). Dislocations or their parts
located in a subsurface layer, microtwin lamellas and
block boundaries are seen as grooves. Dislocations, dis-
location loops, blocks and pipes were found to be the
main defects in ingots. The concentration of these de-
fects depends mainly on the structural quality of seed,
its preparation and growth conditions. Our results have
shown that the main reasons of these defects formation
are:
1) Conditions of growing. Defects of crystalline structure
can appear at different stages of crystal growth. But
the majority of defects are generated at the initial
growth stage due to the formation of 3C-SiC. This
modification of SiC is of low stability; it transforms
to a-SiC at high temperature. This transformation
leads to the emergence of pores, inclusions and pipes
in growing crystals. Correct selection of Ar pressure
at the initial growth stage allows one to avoid the for-
mation of 3C-SiC. Moreover, the stability of growth
conditions (temperature of growth, pressure and va-
por equilibrium) also essentially influences the struc-
tural perfection of crystals.
2) Fixation of the seed. Pipes can be caused by defects in
the graphite seed-holder and incorrect fixation of a
seed.
3) Quality of the seed. The largest part of defects can
originate from the defects of the seed crystal and its
surface. Therefore, to obtain high-quality crystals one
should carefully choose seed crystals.
Shown in Fig. 2 is the appearance of the typical SiC
crystals obtained by the Lely method and used as a seeds
Fig. 1. Design of the equipment: 1 � crucible of vacuum-tight
graphite, 2 � heater, 3 � first screen, 4 � second screen, 5 �
rotated rod.
Fig. 2. The appearance of the typical SiC crystals obtained by
Lely method (1) and ingots (2,3) grown in this work. Time of
growing: 2 � 5 hours, 3 � 10 hours.
S. F. Avramenko et al.: Investigation of structural perfection of SiC ingots grown ...
7 8 SQO, 2(1), 1999
(1) and ingots (2,3) grown in this work. Fig. 3 shows the
schematic cross-section of the ingot along the C axis. It
can be conventionally divided into three parts taking into
account a content of defects: the seed (1), the monocrys-
talline part (2), the outer part (3). The blocks in the area
(3) frequently consist of various polytypes (15R, 6H, or
4H) differing from the polytypes of the seed (6H-SiC)
and of the growing crystal (6H- or 4H). Significant elas-
tic deformations arise at the part (3), these sometimes
extend into the area (2).
Fig. 4 represents the Raman spectra for various parts
of the ingot. As the absorption coefficient for Ar laser
radiation is small, the Raman spectra give information
about a polytype structure averaged by the entire light
path inside the ingot. The spectra show that the periph-
eral, polycrystalline part and the bulk of the ingot con-
sist of 15R and 6H polytypes, respectively, while the seed-
ingot interface contains the inclusions of the 4H poly-
type.
The shape of the ingots is determined by the configu-
ration of a thermal field used. The main structural de-
fects (dislocations and micropipes) originating from the
seed surface propagate along the vector grad T; they are
normal to the ingot surface.
The polarity of SiC seed (Si-type or C-type plane) in-
fluences the polytype structure of growing crystals. The
difference of the binding energy values for the (0001) C
and (0001) Si surfaces of SiC allows one to control a poly-
type structure of growing crystals [10,11]. Using the
charge caused by doping with boron on the surface of
6H-SiC seed (0001) C, we obtained the 4H-SiC ingots,
while on the (0001) Si surface we always got the 6H poly-
type. This result was obtained in several dozens of exper-
iments at the growth temperature T < 2400 oC. Howev-
er, rising the temperature up to 2500 oC, we obtained only
6H-SiC polytype ingots on the (0001) C surface. Thus,
one can control the polytype structure using (0001) C
surface by varying the technological conditions of growth
(temperature, impurity and so on) [11]. In Fig. 5 the Ra-
man spectra of plates cut from two different ingots are
represented. In the first case, the growth was carried out
on a surface (0001) Si of the seed and, in the second one,
on a surface (0001) C of 6H-SiC seed.
140 160 180 200
0,0
0,5
1,0
1,5
2,0
2,5
3,0
In
te
n
s
it
y
,
a
rb
.u
n
.
Raman shift, cm
-1
3
2
1
4H
6H
15R
140 160 180 200
0,0
0,5
1,0
1,5
2,0
In
te
n
s
it
y
,
a
rb
.u
n
.
Raman shift, cm
-1
2
1
Fig. 3. The shape of the crystal: 1 � seed, 2 � monocrystalline
part, 3 � peripheral part.
Fig. 4. Raman spectra for various sites of the same ingot: 1 �
interface seed/ingot, 2 � mono-crystalline part, 3 � peripheral
part.
Fig. 5. Raman spectra of ingots grown on 6H-SiC seed: 1 �
6H-SiC grown on a surface (0001) Si, 2 � 4H-SiC grown on a
surface (0001) C.
S. F. Avramenko et al.: Investigation of structural perfection of SiC ingots grown ...
79SQO, 2(1), 1999
3. Conclusions
The construction of the crucible designed by us, with a
thermal field of a hemispherical configuration, allows to
conduct effective growth of SiC crystals of large sizes.
Using seeds of 8 to 10 mm in diameter, we received the
plates with the diameter up to 35 mm.
The investigation of structural defects in silicon car-
bide ingots obtained by the modified Lely method has
been carried out. It has been shown that there are three
characteristic parts in the grown crystals that differ by
the defect composition. The main defects are dislocations,
screw dislocations, dislocation loops, blocks and pipes.
The seed/ingot junction area plays the main role of a dis-
location source. The pipes mainly originate from the
boundaries of the seed in peripheral parts of ingots. These
parts of ingots consists of misoriented blocks. The caus-
es of structural defect formation are analyzed. It is shown
that the modified Lely method developed allows to pro-
duce SiC substrates of fairly high quality. In the best
ingots the concentration of dislocations did not exceed
102-103 cm-2, micropipes � 10-20 cm-2, and blocks were
absent.
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