New Phase of sp3-Bonded BN: The 5H Polytype

Article abstract of DOI:10.1021/jp9844664

A new phase of sp³-bonded BN, that is, 5H polytype, has been found. The representative lattice parameters a and c were determined to be 2.528 and 10.407 Angstroem, respectively. The new BN phase was prepared by chemical vapor deposition assisted with 193 nm laser irradiation of the surface. Source gases were diborane and ammonia diluted in argon and hydrogen. The substrate temperature was 850 degC.

Full text of DOI:10.1021/jp9844664

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VOLUME 103, NUMBER 17, APRIL 29, 1999
LETTERS
New Phase of sp3-Bonded BN: The 5H Polytype
Shojiro Komatsu* and Katsuyuki Okada
National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Yoshiki Shimizu and Yusuke Moriyoshi
Hosei UniVersity, College of Engineering, Department of Materials Science, 3-7-2 Kajinomachi, Koganei,
Tokyo 184-8584, Japan
ReceiVed: NoVember 18, 1998; In Final Form: March 12, 1999
A new phase of sp3-bonded BN, that is, 5H polytype, has been found. The representative lattice parameters
a and c were determined to be 2.528 and 10.407 Å, respectively. The new BN phase was prepared by chemical
vapor deposition assisted with 193 nm laser irradiation of the surface. Source gases were diborane and ammonia
diluted in argon and hydrogen. The substrate temperature was 850 °C.
Introduction
Materials with covalent bonds of tetrahedral coordination, i.e.,
sp3 bond, may show polytypism as is well-known in silicon
carbide (SiC), because of variations in the stacking of the
densely packed layers.1 Boron nitride (BN) with this bonding
has excellent physical and chemical properties that are almost
equivalent to and in some cases superior to those of diamond.2
Until now, however, only two sp3-bonded phases of BN have
been registered in JCPDS-ICDD,3 i.e., wurtzite4,5 and cubic
forms;6,7 these are classified into 2H and 3C, respectively,
according to the Ramsdell notation.1 Sp3-bonded BN, carbon,
and SiC are picked up from JCPDS-ICDD3 and classified from
this point of view in Table 1. This paper introduces a new phase
of 5H polytypic BN with sp3 bonds.
Figure 1. 1. Energy-dispersive X-ray spectrum (EDX) of a CVD film.
X-ray intensity peaks from B (KR) and N (KR) are found at around
0.18 and 0.39 keV, respectively.
density. The depositions were carried out for 90 min from the
source gases of diborane (B2H6) and ammonia (NH3) diluted
with the mixture of argon and hydrogen gases. The flow rates
of the gases were as follows: 50 sccm (standard cubic
centimeters per minute) of 5% diborane diluted in argon, 10
sccm of ammonia, 100 sccm of hydrogen, and additional 3 SLM
(standard liters per minute) of argon. The total pressure was 20
Torr. The substrate temperature was kept constant at about 850
°C.
Experimental Section
The films were deposited on mirror-polished silicon (100)
substrates of 1 in. diameter by chemical vapor deposition (CVD)
which was assisted with simultaneous irradiation of the surface
with an ArF excimer laser at 193 nm. The repetition frequency
and energy density of the laser were 10 Hz and 6 W/cm2,
respectively; photochemical effects on the surface reactions are
supposed to be dominant over thermal ones at this energy
Results and Discussion
Compositional analysis (Figure 1) performed by energy-
dispersive X-ray spectroscopy (EDX) at an acceleration voltage
* Corresponding author. E-mail: komatsus@nirim.go.jp.
10.1021/jp9844664 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/10/1999

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3290 J. Phys. Chem. B, Vol. 103, No. 17, 1999
Letters
TABLE 1: Classification of sp3-Bonded Materials from the Point of View of Polytypisma
BN
C
JCPDS-ICDD
19-0268
SiC
Ramsdell notation
JCPDS-ICDD
D (%)
D (%)
JCPDS-ICDD
D (%)
2H
26-0773
1.41
0.86
-1.88
0.00
0.12
29-1126
29-1130
-0.01
0.49
20-0174
this report (70805)
35-1365
3C
4H
6-0675
26-1078
0.00
0.00
29-1129
29-1127
22-1317
42-1360
29-1131
0.00
-0.01
0.17
5H
6H
this report
0.82
-0.77
0.17
26-1082
26-1075
26-1081
0.00
0.00
0.00
8H
10H
bond distance (Å)
distance between planes along c axis (Å)
1.5657
2.0876
1.5444
2.05923
1.8875
2.5166
a The bond distance and the interplane distance are represented by those of 3C (cubic) polytypic forms. D is defined as the deviation of c/(na)
from 0.816 where n is the number in the Ramsdell notation.
Figure 2. 2. X-ray diffraction pattern of the sample of Figure 1. Weak peaks in the high 2θ region are made distinguishable in the inset. This is
the raw data with no computer processing such as smoothing and background reduction.
TABLE 2: Analysis of the X-ray Diffraction Pattern Shown
of 3.0 keV indicated stoichiometric composition with no
in Figure 2 in Terms of the sp3-Bonded 5H Structure of BN
detectable impurities. A high-purity sintered pyrolytic BN disk
(N1 grade BN commercially available from DENKA Co., Inc.,
Japan) was used as a standard. X-ray intensity peaks from B
(KR) and N (KR) are found at around 0.18 and 0.39 keV,
respectively.
in Which the Lattice Parameters a and c Are 2.528 and
10.407 Å, Respectively
h k
l
d (Å) d (observed) error (%)
comment
0 0 3 3.4690
0 0 6 1.7345
1 0 1 2.1425
1 1 1 1.2548
0 0 9 1.1563
3.469
1.757
2.143
1.244
1.1512
0.01 very strong
-1.30 weak, broad
0.00 medium
0.87 medium weak
0.44 weak, broad, observed only
after smoothing and
back ground reduction
0.04 weak
An X-ray diffraction pattern for the sample of Figure 1 was
obtained as shown in Figure 2 by using a fully computerized
film X-ray diffraction system (RIGAKU RINT 2500) in which
the incident X-ray angle was fixed at 0.3° and the voltage and
current applied at the rotating Cu target were 40 kV and 400
mA, respectively. The scanning rate and step in the detector
were 0.02 deg/min and 0.02°, respectively. This pattern proved
to be consistent with a hexagonal lattice where the lattice
parameters a and c were 2.528 and 10.407 Å, respectively, as
shown in Table 2. The crystallite size is estimated to be very
2 0 2 1.0712
1.0708
fine, about 100 Å, from the broadness of the XRD peaks by
using the Scherrer’s equation.
This hexagonal lattice is best understood in terms of a 5H
polytypic form of sp3-bonded BN. The deviations of a from

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J. Phys. Chem. B, Vol. 103, No. 17, 1999 3291
TABLE 4: Analysis of the X-ray Diffraction Pattern Shown
in Figure 3 in Terms of the sp3-Bonded 5H Polytypic Form
of BN in Which the Lattice Parameters a and c Are 2.5431
and 10.3668 Å, Respectively
h
k
l
d (Å)
d (observed) error (%)
comment
0
0
0
1
0
0
0
0
3
6
9
1
3.4556
1.7278
1.1519
2.1543
3.456
1.724
1.151
2.154
0.00
0.23
0.06
0.00
very strong
very weak, broad
very weak, broad
medium strong
TABLE 5: Comparison of JCPDS-ICDD 26-0773 (Wultzite
BN) with the Sample of Figure 3
JCPDS-ICDD
26-0773
70805
intensity
h
k
l
d (Å)
intensity
d (Å)
1
0
1
1
1
1
1
2
2
0
0
0
0
0
1
1
0
0
0
2
1
2
3
0
2
2
3
2.211
2.114
1.959
1.528
1.188
1.277
1.980
0.980
0.870
0.840
100
70
45
18
16
25
12
<1
<1
<1
2.26
2.10
1.99
100
84
46
1.19
15
Figure 3. X-ray diffraction pattern of a sample indicating the growth
of wBN together with the 5H polytypic BN.
TABLE 3: Analysis of the X-ray Diffraction Pattern Shown
in Figure 3 in Terms of the Wurtzite Structure (2H) of BN
in Which the Lattice Parameters a and c Are 2.6069 and
4.1771 Å, Respectively
under the same condition, but for the laser irradiation, yielded
only amorphous films.
The enhancement of the growth of sp3-bonded BN by 193
nm laser irradiation was previously discussed using the molec-
ular orbital method, where the photochemical depassivation of
the nitrogen (100) surface of cubic BN under CVD conditions
was predicted.8 The passivation of that surface by atomic
hydrogen is regarded as one of the major obstacles to the CVD
growth of sp3-bonded BN2. Further reviews on the growth of
the cubic form of sp3-bonded BN from the vapor phase by
various techniques are found in the literature,9,10 while technical
aspects of BN preparation methods are reviewed in a recent
volume.11
h
k
l
d (Å) d (observed) error (%)
comment
1
0
1
1
0
0
0
0
0
2
1
3
2.2576
2.0886
1.9861
1.1851
2.258
2.103
1.988
1.185
0.00
-0.69
-0.08
0.00
medium strong, broad
medium strong, broad
medium, broad
weak, broad
the ideal a, which is based on the bond distance of cubic BN
(JCPDS-ICDD 35-1365), in this sample and wurztite form
(JCPDS-ICDD 26-0773) are -1.1% and -0.15%, respec-
tively. On the other hand, the deviations in c in this sample
and the wurtzite form are +0.67% and +1.27%, respectively.
The deviations in our sample may be considered to be within
the allowed values suggested by the data of the wurtzite form.
In an ideal close-packed structure, the ratio of interplane
Summary
A new phase of sp3-bonded BN of the 5H polytypic form
was found. It was grown under CVD conditions with the
assistance of 193 nm laser irradiation on the surface.
x
distance (c/5 in our case) to a is 2/3, i.e., 0.8165 (ref 1). The
deviation from this value is regarded as an indicator of the
degree of elongation (compression) of the bond along the c axis
if the sign is plus (minus). These data are also summarized in
Table 1. We at first notice that the bonds in the wurtzite BN
are not isotropic but elongated along the c axis. This seems to
support the data in our sample, +0.82%, in comparison with
those for the wurtzite form, 0.86 and 1.41%. The deviation in
5H polytypic SiC, 0.77%, is also very close to that of our
sample. We found these indications of the 5H polytypes in at
least 15 samples. We further notice that “diamond” polytypes,
which have no stoichiometric polarity, show ideally close-
packed structures, on the other hand.
We briefly refer to another sample, which was prepared under
almost the same conditions as above, indicating the growth of
wurtzite BN (wBN). The deposition duration was 60 min in
this case. The XRD pattern (Figure 3) is best understood in
terms of the mixture of sp3-bonded 5H BN and wBN as shown
in Tables 3 and 4. It is noteworthy that the intensity ratio of
the XRD peaks is in good agreement with those for the powder
XRD data (JCPDS-ICDD 26-0773) as seen from Table 5. The
critical condition to determine which phase should dominantly
grow is still not clear. It should be also noted that the depositions
Acknowledgment. We are grateful to Messrs. T. Wada and
M. Tsutsumi for their help in XRD and EDX, respectively. This
study was partially supported by Special Coordination Funds
for Promoting Science and Technology, the Science and
Technology Agency, Japan.
References and Notes
(1) Verma, A. R.; Krishna, P. Polymorphism and Polytypism in
Crystals; John Wiley & Sons: New York, 1966.
(2) See the references in Komatsu, S.; Yarbrough, W.; Moriyoshi, Y.
J. Appl. Phys. 1997, 81, 7798-7805.
(3) International Centre for Diffraction Data, PA.
(4) Bundy, F. P.; Wentorf, R. H., Jr. J. Chem. Phys. 1963, 38, 1144-
1149.
(5) Soma, T.; Sawaoka, A.; Saito, S. Mater. Res. Bull. 1974, 9, 755-
762.
(6) Wentorf, R. H., Jr. J. Chem. Phys. 1957, 26, 956.
(7) Wentorf, R. H., Jr. J. Chem. Phys. 1961, 34, 809-812.
(8) Komatsu, S. J. Mater. Res. 1997, 12, 1675-1677.
(9) Moriyoshi, Y.; Komatsu, S.; Ishigaki, T. Key Eng. Mater. 1995,
111/112, 267-280.
(10) Konyashin, I.; Bill, J.; Aldinger, F. Chem. Vapor Deposition 1997,
3, 239-255.
(11) Narula, K.; Chaitanya, Ceramic Precursor Technology and Its
Applications; Marcel Dekker: New York, 1995.