SILICON AND BORON CARBONITRIDE FIMLS OBTAINED
BY CVD METHODS
N.I.Fainera), M.L.Kosinovaa), V.S. Sulyaevaa), Yu.M.Rumyantseva),
E.A.Maximovskiia), B.M.Ayupova), B.A.Kolesova), F.A.Kuznetsova),
V.G.Kesler b), M.Terauchi c), K.Shibatac), F.Satoh c), Z.X.Caod)
a)
Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia,
630090, b)Institute of Semiconductor Physics SB RAS, Novosibirsk,
Russia, 630090, c)IMRAM, Tohoku University, Sendai, Japand)Institute of
Physics CAS, P.O. Box 603, Beijing 100080, P.R. China
Nanocrystalline hard silicon carbonitride films were synthesized
by RPECVD using the gas mixture of hexamethyldisilazane with
ammonia and helium within temperature range of 723-1073 K. IR and
Raman spectroscopy, AES, XPS, ellipsometry, XRD using the
synchrotron radiation, SEM, HREM, SAED, AFM, measurements of
hardness by nanoindenter and spectrophotometry measurements were
applied to study their physicochemical properties. The SiCxNy films
exhibit high optical transmittance in the spectra range of 1200-2200 nm.
Microhardness of these films increases from 18 to 28 GPa, while Young's
modulus changes from 135.5 to 185.5 GPa with Si-C bonds content.
Boron carbonitride films were deposited on silicon wafers by low
pressure chemical vapor deposition from gaseous mixture of
trimethylamino borane (TMAB) or triethylamino borane (TEAB)
complexes and ammonia, nitrogen or helium. BCxNy films with different
composition were obtained by varying composition of initial gas mixture
and deposition temperature. BCxNy films with microhardness up to 40
GPa was synthesized.
Part I. Nanocrystalline films of silicon carbonitride: chemical
composition and bonding and functional properties
Introduction
Si–C–N nanocomposite materials are of great scientific and
technological interest because of wide spectra of their remarkable
properties from high hardness, superplasticity to a high strength and
47
toughness depending on the composition as well as their excellent high
temperature properties, enhanced oxidation and corrosion resistance.
The enhancement of these properties has been attributed to complexcovalent chemical bonding and a low oxygen diffusion coefficient in the
structure of the silicon carbonitride. The nanocrystalline SiCxNy
materials are chemically and thermally stable, and they possess wide
bandgap and high hardness of 27-42 GPa. Currently, silicon carbonitride
films have been produced with ion sputtering deposition of carbon and
silicon in nitrogen atmosphere, N+ implantation into SiC surface, laser
vapor phase reaction of hexamethyldisilazane (HMDS) with ammonia,
chemical vapor deposition (CVD) and plasma enhanced CVD using
Si(CH3)4-NH3-H2,
SiH4-NH3(N2)-CH4
(or
N2 H 4)-H2(Ar),
SiCl 4+NH3+C3H8+H2 , as initial atmospheres (1-4). The use of
siliconorganic compounds has attracted interest due to these compounds
containing the silicon, nitrogen and carbon, can serve as precursors for
Si 3 N4 , SiC or Si–C–N ceramics, powders and films. The nature of the
organic groups bound to silicium influences the physical and chemical
properties of polysilazanes as well as the Si–C–N compounds after
conversion. The molecules of HMDS contain the -C-Si-N-Si-C- bridges
ready for preparation of the final nanocomposite material. The SiCxNy
obtained via the plasma enhanced chemical vapour deposition of
organometallic compounds exhibit improved thermo-mechanical
properties in comparison with conventionally processed.
The goal of our research is the study of physical and chemical,
functional properties of nanocrystalline SiCxNy films and determination
of correlation between functional properties and chemical composition
and bonding.
Еxperimental
Nanocrystalline SiCxNy films were synthesized in wide interval of
chemical composition: from composition close to SiC up to one close to
Si 3 N4 . The synthesis was carried out by remote plasma enhanced
decomposition of hexamethyldisilazane (HMDS) as single-source precursor
using two gas mixtures: (HMDS+He) and (HMDS+ NH3+He) in
temperature range of 723-1073 K and total pressure in reactor of (4-6)  102
Torr (5). Initial PNH3/PHMDS ratios were equal to 0.3, 0.73, 1.0, 1.7, and 2.1.
The effect of the growth temperature, chemical composition of the initial gas
48
phase, r.f. plasma power, total pressure in the reactor on the formation of
certain microstructure, chemical and phase composition of the growing films
were studied. The influence of chemical composition on physical and
chemical properties of the obtaining silicon carbonitride films was
investigated using a complex of modern methods: IR and Raman
spectroscopy, high-resolution electron micrography (HREM), selected area
electron diffraction (SAED), scanning electron microscopy (SEM), atomic
force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Auger
electron spectroscopy (AES), optical measurements, and XRD - SR. The
hardness of films was measured by the Vickers indentation method. The
indentation tests were carried out using a CSZM Nano Hardness tester
under a load of 5 and 10 mN.
Results and discussion
The thickness of synthesized silicon carbonitride films were
2003000 nm. Chemical composition of these films was examined using
spectroscopic methods: IR and Raman spectroscopy, AES and XPS.
IR-Spectroscopy. According to the data of IR spectroscopy, a
wide band of 450-1200 cm -1 is observed in the spectra of films
synthesized within the whole of investigated temperature range.
Hydrogen-related bonds were not detected. Mathematical analysis of the
IR spectra of SiCxNy films was carried out. For this purpose, the main IR
spectrum was approximated by a sum of three Gaussian curves and their
integral intensities were calculated. This analysis showed that the main
IR adsorption band mostly corresponds to the superposition of
asymmetric stretching vibration of Si-N-Si bonds at 450 cm-1,
symmetric stretching vibration of Si-N bonds at 950 cm-1, and stretching
vibration of Si-C bonds at 800 cm-1. Apparently, the above-mentioned
positions of vibration modes slightly differ in ternary films. The
incorporation of C into Si-N network damages the symmetric vibration
modes of Si-N bonds of binary compound, thus shifting their absorption
bands. Realized analysis of IR spectra revealed that the integral intensity
ratios as I(Si-C)/I(Si-N) depend on the growth temperature and the
PNH3/PHMDS ratios. The rise of the temperature up to 1073 K leads to the
monotonic increasing of these rations in IR-spectra of films grown in
(HMDS+He) gas mixture. Opposite the rise of ammonia concentration
in (HMDS+NH3+He) system and the growth temperature leads to
increase of concentration of Si-N bonds in films.
49
Raman Spectroscopy. Raman spectroscopy is a sensitive tool that
provides valuable structural information on the translation symmetry of
materials, and so is useful for the study of disorder and crystalline
formation. The Raman spectra of the SiCxNy films were analyzed in a
similar manner as that used for carbon films. The G mode is due to the
stretching vibration of any pair of sp2 atoms in both chains and rings,
whereas the D mode is related to the breathing vibration of sp 2 sites only
in rings. Thus, an increase in I(D)/I(G) is ascribed to an increase in the
number and/or in the size of sp2 clusters. Fig. 1a illustrates the typical
Raman spectrum of SiCxNy film. The band of 1200-1600 cm-1 was
deconvoluted, using Gaussian line shapes, into D and G bands. The
dependence of the integral intensity ratios of the D and the G bands on
the growth temperature and the PNH3/PHMDS ratios are given in Fig.1b and
Fig.1c, respectively. As appears from these data, the rise of temperature
leads to the decrease of the intensity of the D band, but the increase of
ammonia concentration promotes to an increase of the D band intensity.
These regularities seemingly connect with increase of nanocrystal size
with the growth temperature rise and decrease of nanocrystal size due to
the increase concentration of nitrogen in films.
b
G
Si(100)
2LO
c
- HMDS+NH3+He
4,5
- HMDS+He
4,0
4,2
I(D)/I(G)
5,0
D
)
I(D)/I(G)
Intensity
a
3,5
3,0
2,5
2,0
)
)
Tsynthesis= 873 K
4,0
3,8
(HMDS+NH3+He)
3,6
1,5
1,0
3,4
0,5
0,0
800
1000
1200
1400
1600
-1
Raman shift (cm )
1800
3,2
700
800
900
1000
1100
Tsynthesis, K
1200
1300
0,0
0,5
1,0
1,5
2,0
PNH /PHMDS
3
Fig. 1. Typical Raman spectra of SiCxNy film–(a); the I(D)/I(G) ratio as
function of the growth temperatures at PNH3/PHMDS=1.6 – (b) and
ammonia concentration in gas mixture– (c).
AES and XPS study. Characterization of the atomic bonding was
performed using XPS and AES. Before the measurements the SiCxNy
films were etching in weak dilution of HF acid to eliminate any surface
impurities adsorbed during air handling and no destruct any chemical
50
2,5
bonds in the films. AES study showed that the synthesized films are
characterized by good homogeneity of chemical composition over
thickness, as it follows from Fig. 2a. Because of the inherent
uncertainties in the energy referencing due to sample charging it was
impossible to determine the exact XPS and AES peak positions. Instead,
in order to circumvent this limitation for the Si component the Auger
parameter ( which is determined by measuring the energy difference
between the Si 2p (XPS) and Si KLL (bremsstrahlung-excited AES)
peaks was obtained. As the Auger parameter is an energy difference
value, it is charge independent and uniquely defines the bonding
configuration of the elements under analysis. The Auger parameters for
Si, SiO 2, Si 3 N4 , SiC are equal to 1716.1, 1712.2, 1714.45, 1716.05 eV,
respectively (6). It was found that linear dependence of the Si Auger
parameter values on the growth temperature is closely related monotonic
change of character of surrounding of Si atoms in SiCxNy films (Fig. 2b).
The Si Auger parameter of SiCxNy films grown from (HMDS+He)
mixture in the temperature region of 523 – 973 K change from 1714.2
up to 1715.0 eV which lie midway between that of Si3 N4 (1714.45 eV)
and SiC (1716.05 eV). The temperature rise leads to such Si electron
configuration which has a bonding scheme involving both mainly C and
negligibly N.
1,0
Concentration
0,8
1715,2
The Auger parameter, eV
0,9
a
0,7
0,6
C
0,5
0,4
0,3
0,2
0,1
0,0
Si
N
O
0
50
100
150
200
250
300
1715,0
b
1714,8
(HMDS+He)
1714,6
1714,4
1714,2
1714,0
1713,8
(HMDS+NH3+He)
1713,6
PNH / PHMDS =1.6
400
3
500
600
700
800
900
1000
1100
1200
Tsynthesis, K
Sputtering time (min)
Fig. 2. Typical AES depth profile of distribution of chemical elements in the
SiCxNy film grown from (HMDS+He) – (a). Dependence of the Si Auger
parameter on the growth conditions – (b).
51
2
C 1s
973
K
873
773
K
673
K
K
873
773
K
673
K
K
C(sp )-N
C-C
C-Si
Si-C
973
K
Si-N
N-Si
Si 2p
2
N 1s
N-C(sp )
At addition of ammonia to initial gas mixture the Si Auger
parameter of SiCxNy films grown in the temperature region of 673 – 973
K changes from 1713.7 up to 1714.3 eV. Last fact was explained that Si
- N bonds predominate in network with the temperature increase. XPS
analysis gives direct information about the composition and the bonding
type of atoms in solid phases. Chemical shift in bonding energy of
photoelectron peak occurs when there is a change in valence state of the
bonding atoms. Fig. 3 shows the evolution of N 1s, Si2p and C 1s XPS
spectra of SiCxNy films as a function of growth temperature in the region
of 673-973 K and chemical composition of initial gaseous mixtures.
673
K (HMDS+NH3+He)
773
K873
K PNH3/PHMDS=1.6
Intensity, arb.units
973
K
673
773
K
K
873
K
402
400
398
396
394
773
K
673
773
K
K
873
K
104
873
K
673
K
(HMDS+He)
102
100
98
288 286 284 282 280
Binding energy, eV
Fig. 3. N 1s, Si2p and C 1s XPS spectra of SiCxNy films as a function of
growth temperatures and chemical composition of initial gaseous
mixtures.
In case of films grown using (HMDS+He) mixture the N 1s spectra
could be deconvoluted into main peak with binding energy of ~ 397.5
eV, corresponding to N-Si bonding, and negligible peak with binding
energy of ~ 398.8 eV, corresponding to N-C(sp2) bonding. The Si 2p
spectra could be deconvoluted into 3 subpeaks with binding energies of
~ 102.8, 101.7 and 101.0 eV. The first component has less intensity and
52
corresponds to Si-O bonding (oxygen is impurity in SiCxNy films). The
component with binding energy of ~ 101.7 eV closes to peak of
stoichiometric silicon nitride. The third component with binding energy
of ~ 101.0 eV is intermediate position between Si-N and Si-C bonding.
Thus, in these films SiC compound was not disclosed but component
with binding energy of ~ 101.0 eV indicates to the existence of
polysubstituted tetrahedrons (CnSiN4-n) due to partial replacement of N
atoms in Si-N bonding by C atoms. The C 1s XPS spectra could be
deconvoluted mainly into 3 subpeaks with binding energies of ~ 283.2,
284.6, 286 eV, corresponding to C-Si, C-C and C(sp2)-N bonding,
respectively. With rise of the growth temperature, the total C
concentration in films increases up to 60 % exceeding initial
concentration in HMDS molecules (44.7%), and the total N and Si
concentrations monotonically decrease and become low then their
concentrations in HMDS. Addition of ammonia to initial gas mixture
promotes the formation of SiCxNy films of high concentration of
nitrogen from 30% up to 50% (more higher then in HMDS) with the
temperature rise. Contrarily, C concentration decreases from 28% up to
5% and becomes in these films more less then in HMDS at analogous
change of the growth conditions. The components of Si2p and C1s
spectra with binding energies of ~ 101.0 and 283.2 eV, respectively,
monotonically decrease with the temperature rise. This fact is evidence
of the primary tendency to the formation of SiCxNy films close to
stoichiometric silicon nitride at high temperatures.
Microstructural features. Investigation of the micromorphology of
surface by SEM and AFM showed that the films synthesized from gas
mixtures (HMDS+He) and (HMDS+NH3+He) exhibit uniform
distribution of tightly packed nanocrystals. Their size increases from 10
up to 20 nm with temperature rise. Besides, more large scale
conglomerate formations (50-100 nm) consist of tens of fine
nanocrystals were observed. Fig. 4 gives AFM images of SiCxNy films,
which show a very smooth surface with a root mean square roughness of
0.5-0.7 nm. The temperature rise leads to increase of average size of
grains a in the films prepared from (HMDS+He) gas mixture: at
temperatures of 773 and 973 K grain sizes are 20 and 80 nm,
respectively (Fig. 4a-b). Addition of ammonia to (HMDS+He) promotes
decrease size of grains until 40 nm in film synthesized at same
temperature of 973 K (Fig. 4, c). Transmission Electron Microscopy was
53
employed to investigate the microstructure of the SiCxNy films. In the
vicinity of the interface between the substrate and film the HREM images
and SAED pattern of these films were shown in Fig. 5a. It was clearly seen
that SiCxNy films are composed of nanocrystals embedded in the
amorphous phase. The SAED pattern consists of a halo and weak
diffraction rings indicating the presence of the amorphous and crystalline
constituents in this film. Their size depends on the growth temperatures and
initial gas composition: more large scale grains (~ 2 nm at 773 K) form in
case of using (HMDS+He) gas mixture (Fig. 5a); addition of ammonia leads
to decreasing of particles size (less 1.5 nm) at the same growth conditions
(Fig. 5c). The temperature rise until 823 K promotes increase of their size to
~ 5 nm. Fig. 5b shows the augmented HREM image of several nanocrystals
indicated in Fig. 5a. The d spacings appearing in the HREM image of
nanoparticles were measured to be 0.24 nm and 0.21 nm. These values are
consistent with the d-values calculated for the 1st and 2nd rings in the
SAED pattern. The d-spacing of the 3rd ring in SAED pattern is not
observed in this HREM image.
a
c
b
)
a = 20 nm
Rrms= 0.5 nm
a = 40 nm
Rrms= 0.6 nm
a = 80 nm
Rrms= 0.7 nm
Fig. 4. AFM images of SiCxNy films obtained using (HMDS+He) system at 773
K – (a) and 973 K (b) temperatures and using (HMDS+ NH3+He) gas
mixture at 973 K – (c).
It may be that the d-value of 0.15 nm is critical to resolve by the
performance of the TEM used. Obtained SAED d spacings are close to
-Si 3 N4 (7).
a
)
b
)
c
)
54
0,21
nm
0,24
nm
Fig.5. Cross-sectional HREM images of SiCxNy films grown at 773 K using
(HMDS+He)-(a, b) and (HMDS+ NH3+He)-(c) gas mixtures.
10
Si(400)
100
30
40
50
60

70
80
7000
6000
5000
4000
3000
2000
1000
0
10
20
(101
)
Intensity
?
55
(500)
(220)
1000
c
8000
(212)
(421)
(504)
Intensity
(512)
(203)
(103)
?
(312)
(303)
Si(400)
(114)
100
(210)
Intensity
1000
(302)
(222)
(312)
(320)
b
10000
(101)
a
(200)
10000
(322)
The structure and phase composition of SiCxNy films were
investigated at the station «Anomalous scattering» of the Siberian Center
of Synchrotron Radiation (INP SB RAS) by XRD-SR technique
specially developed by us for thin films containing of lightweighed
elements (8). Shown in Fig.6 the diffraction patterns of SiC xNy samples
are typical ones for all silicon carbonitrides films grown in all interval of
growth conditions. The comparison of the interplanar distances suggests
that the lattice parameters of hexagonal unit cells of SiCxNy and -Si 3 N4
(7) are close within the experimental errors (8). Inasmuch as, both IRspectroscopy and XPS analysis indicates on presence of complex
bonding between Si, N and C elements in the films we can imply that
carbon atoms substitute only for the silicon sites without changes in
valency in the -Si 3 N4 structure so that C and Si are always “bridged”
by nitrogen in the SiCxNy films. On the broadening of diffraction peak,
we estimated the size of nanocrystals. Their size varied from 5 to 50 nm,
depending on the growth conditions. There is good coincidence in
microstructural data obtained by SEM, AFM, TEM and XRD-SR
techniques.
Microhardness measurements. CSZM Nano Hardness tester was
used to determine the mechanical properties of SiCxNy/Si(100) samples
of 1-2 m thick. A Berkovich diamond pyramidal tip and a single
loading – unloading cycle in the coordinates: load – depth of the
indenter penetration were applied.
90
100
-1000
10
20
30
40
50

60
70
80
20,5

21,0
Fig.6. XRD-SR patterns of SiCxNy films grown at 1073 K using (HMDS+He) –
(a) and (HMDS+NH3+He) - (b) gas mixtures; =1.5405 A. (c) – the
enlarged image of (101) peak of XRD pattern (b).
Measurements were carried out with the maximal load of 5 and 10 mN
and with indenter penetration depth restricted up to 140 nm. The
analysis of these curves according to Oliver and Pharr’s procedure
allows determining microhardness and elastic modulus of these thin
films. Measurements showed that the microhardness of silicon
carbonitride films is from 18 to 28 GPa, while Young's modulus changes
from 135.5 to 185.5 GPa. The increase of concentration of Si-C bonds in
films grown in (HMDS+He) gas mixture is accompanied by the increase
of hardness values from 18 up to 28 GPa (Fig. 7). In case of films grown
in gas mixture with ammonia the increase of growth temperature leads to
the decrease of hardness values from 28 to 20 GPa that may be
connected with high concentration of Si-N bonds. Obtained results are
in good agreement with references for commercial silicon carbide (32
GPa) and silicon nitride (20 GPa).
The optical properties. The SiCxNy films grown on fused silica
substrates from (HMDS+He) mixture exhibited high optical transmittance
(~ 80-90 % for =1200-2200 nm). The SiCxNy films grown from
(HMDS+NH3+He) gas mixture have very high optical transmittance (~
85-95 % for =600-2200 nm). Adsorption of the SiCxNy films occurred in
the below 370 nm range of wavelength, beyond which these films
demonstrated excellent transparency, characteristic for wide band gap
materials. A progressive blue shift of the steepest part in the absorption
band was observed with adding of ammonia to initial gas mixture but
growth temperatures rise leaded to red shift. Tauc’s formula was used to
estimate bandgap of our films. The bandgap of the films change from ~ 4.2
eV for SiCxNy films having high concentration of nitrogen to ~ 2 eV for
samples having low content of N. The bandgap of Si3N4 is 5.0 eV which
indicates that the SiCxNy films with high content of N close to silicon
nitride.
56
2,0
Si2p(Si-N(C)/Si2p(Si-N)
Si2p(Si-N(C)/Si2p(Si-N)
2,5
2,4
2,3
2,2
2,1
(HMDS+He)
2,0
1,9
1,8
1,5
1,0
(HMDS+NH3+He)
0,5
0,0
1,7
650
700
750
800
850
650
900
700
750
800
850
26
24
HV of Si3N4 - 20 GPa
H, GPa
H, GPa
28
900
950
1000
T growth, K
T growth, K
SiC - 32 GPa
(HMDS+He)
28
27
HV of Si3N4 - 20 GPa
26
SiC - 32 GPa
25
24
22
23
HMDS+NH3+He
22
20
21
18
750
20
800
850
900
950
1000
760
780
800
820
840
860
880
Tsynthesis, K
Tsynthesis, K
Fig.7. Dependence of Si2p(Si-C)/Si2p(Si-N) ratio and hardness of
SiCxNy films on the growth conditions.
PART II. Synthesis, nanoindentation and AFM studies of CVD boron
carbonitride films
Introduction
Compounds of the B-C-N ternary system are of considerable
interest as promising materials for electrical, optical and mechanical
applications. During the recent years, much attention is paid to the
synthesis of thin films of boron carbon nitride (BCxNy) and to the
investigation of their physicochemical properties. However, the optical,
electrical, mechanical, and tribological characteristics, as well as their
dependence on chemical and phase composition of films are still
insufficiently investigated.
Some authors studied mechanical characteristics of boron
carbonitride films (9 – 15). BCxNy films were obtained by chemical
vapor deposition (CVD) from a mixture of diborane with methane and
nitrogen (9, 10). It was established that microhardness (Н) of the
samples of the composition B0,106-0,554C0,751-0,252N0,117-0,145 is changed from
57
5 to 29 GPa, while that of compositions BC1.1N1.4, BC1.5N1.2, BC1.6N2.5,
BC3.7N0.8 is changed from 7 to 13 GPa. The films obtained by reactive
pulsed laser ablation from graphite and h-BN were characterized by
microhardness 2,9 GPa (for the composition of BC2N) (11).
Nanocrystalline B0,42C0,33N0,25 films prepared using the electroncyclotron-wave-resonance plasma assisted deposition had Vicker’s
microhardness over 28 GPa, and Young’s modulus was 240 GPa (12).
BCxNy films synthesized by dual cesium ion sputtering had the hardness
30,6 GPa and stoichiometry BC0,9N0,7 (13). All the authors note regular
increase in microhardness of the samples with an increase in carbon
content in the boron carbonitride films. Influence of composition and
structure on the mechanical properties of BCxNy coatings was studied in
(14), where it was shown that microhardness of maximum 20 GPa was
achieved in the range of approximately 20-45 at.% carbon, affected by
the way of its incorporation into the hexagonal turbostratic lattice as well
as by the crystallite size and texture. The films of both c- BCxNy and hBCxNy were studied in (15). It was defined that with an increase in the C
content, the content of a cubic phase in films was reduced, and the
structure of films changed from cubic phase to hexagonal phase at more
than 13,1 at.% content of the carbon., while the hardness value of 60
GPa was reduced to 10 GPa, respectively. For comparison, according to
literature data, Vicker’s hardness of the h-BN is 20, of the c-BN – 53, of
the diamond – 88 GPa (16).
Experimental methods
In this work, synthesis of BCxNy layers was carried out by low
pressure chemical vapor deposition (LPCVD). The scheme of the
experimental set-up was described previously (17). The precursor was a
volatile elementorganic compound containing all the elements necessary
for the synthesis (B, C, N): trimethylamine borane complex
(CH3)3NBH3 or triethylamine borane complex (C2H5)3NBH3. These
compounds are uninflammable and stable to the action of the
atmosphere; their use in technology is preferable in comparison boron
trichloride or diborane. In addition, these compounds have rather high
vapor pressure, which allows using them as a single-source precursors in
gas-phase processes. The temperature of the TMAB and TEAB sources
was constant and equal to 0 oC and 20 oC, correspondingly. Polished
single crystal silicon plates Si(100) were used as substrates. Various
58
chemical composition of BCxNy films were realized by changing
precursor type, the composition of initial gaseous mixture and deposition
temperature. The films were deposited from the gas phase containing a
mixture of TMAB or TEAB with ammonia, nitrogen or helium within
temperature range of 400 - 700 oC. The process was carried out at low
pressure, P = (2  4)·10-2 Torr and with different TMAB:NH3 (He) and
TEAB: NH3 (N2 or He) ratios. Physicochemical and functional
characteristics of boron carbonitride films were studied with use of wide
variety of above-mentioned methods.
Results and discussion
The thickness values of the BCxNy films were in the range of 200 1000
nm. Refractive index had values from 1,9 to 2,8; growth rate was 50 
130 A/min within the investigated range of synthesis conditions. All
films had a good adhesion to the Si(100) substrate. Morphology of the
film surface was studied by means of SEM and AFM techniques.
Electron microscopic images of the film surface (Fig. 9a-9c) indicate
that the surface is smooth, uniform, has no pores and is tightly packed
crystallites. During CVD process from both TMAB and TEAB
nanocrystalline films BCxNy are formed. The size of crystallites
increases with increase of deposition temperature. AFM images of the
surface of these films (Fig. 10) show similar results. The size of the
particles increases with growth temperature from 10 nm (Tdep. = 400oC)
to 60 nm (Tdep. = 700oC). At the temperature above 500 oC it is observed
self-organization of grains to large-scale crystallites of pseudohexagonal form, size, which obtains 350 – 460 nm. Surface morphology
of the films is characterized by root-mean-square roughness, which is
within the range 1 - 4 nm. More information on microstructure of the
BCxNy films can be found with use of cross-sectional high resolution
transmittance electron microscopy. HREM image of a part of film near
interface shows the nanometer crystals with size of 2-3 nm embedded in
an amorphous matrix (Fig. 9d).
59
a
b
c
d
Fig. 9. SEM images of surface of BCxNy films (a, b, c), synthesized from
TMAB+He mixture at Tdep.=700 oC (a) and 600 oC (b), and from
TMAB+NH3 mixture at Tdep.=700 oC. HREM image of BCxNy film
deposited from TMAB+He mixture at T dep.=600 oC (d).
Chemical composition of films was studied by Auger electron
spectroscopy. Main components: boron, carbon, nitrogen as well as
oxygen (impurity at the level up to 3 at. %) are determined by this
method (Fig. 11a). AES studies revealed that films have a good
uniformity of chemical composition (Fig. 11b). BCxNy films synthesized
from a mixture of TMAB with helium at the temperature of 450 and 500
o
C had chemical composition B0,72C0,23N0,04O0,01 and B0,68C0,27N0,04O0,01,
respectively. Addition of ammonia leads to increasing of nitrogen
content in the films. Increase of deposition temperature promotes growth
of carbon content in the BCxNy films.
60
b
a
Fig. 10. AFM images of surface of BCxNy films deposited from TEAB+NH3
mixture (PNH3 = 4 x 10-3 Torr) at Tdep.=700 oC(a) and 500 oC (b).
AES spectra of the sample M 71:
(1)-surface, (2)-centre of the film.
b
2
1
O
B
C
AES depth profile of the sample M 71.
AES signal intensity d(ExN(E))/dE (arb.units)
AES signal intensity d(ExN(E))/dE (arb.units)
a
0
N
Si
B
C
N
O
50
100
150
200
250
Sputtering time (min)
0
100
200
300
400
Kinetic energy (eV)
500
600
Concentration
B
C
N
O
---------------------------------------------------------Surface
0.46 0.21 0.28 0.05
Centre of the film 0.54 0.14 0.29 0.03
Fig. 11. Typical AES spectrum of surface and profile of distribution of elements
in the BCxNy film, deposited from TMAB+NH3 at T dep. = 400 oC.
61
Depending on conditions of synthesis, boron carbon nitride films can
have different composition and structure: from boron nitride to a ternary
compound BCxNy. The IR spectra of the obtained films revealed the
presence of bonds characteristic for h-BN and BCxNy. The bands at 1380
and 800 cm-1 are characteristic to the hexagonal boron nitride and relate
to the in-plane B-N stretching and out-of-plane B-N-B bending
vibrations. Boron carbide has only one absorption band at 1100 cm-1.
The absorption band in the region of 1250 – 1450 cm-1 is assigned to
C=C and/or C – N stretching vibrations (18). The IR spectra of the films
synthesized at T = 700 oC with different partial pressure of ammonia in
the initial gas mixture were obtained (Fig. 12a). The spectrum is close to
the one of the hexagonal boron nitride. An increase in ammonia
concentration causes changes in the IR spectrum of the films; we
observe an increase in the intensity of the peak at 780 cm-1 which is
attributed to the interplanar vibrations of B – N – B. For the films
synthesized from a mixture of TMAB with helium, there is one broad
peak between 600 and 1600 cm-1 in the IR spectrum (Fig. 12b); the
fitting of this peak gives a superposition of two Gaussian curves
corresponding to the stretching vibrations of B-C and B-N bonds. This gives
us reason to assume that a ternary compound (boron carbon nitride) is
formed in this case. The same IR spectra were obtained for films grown
from mixture of TEAB+NH3.
We carried out X-ray phase analysis of the films using the
synchrotron radiation. The diffraction pattern obtained with -2
scanning procedure is shown in Fig. 13. The diffraction patterns contain
peaks which correspond to the phases of boron carbide and hexagonal
boron nitride and also unknown peaks. At higher concentration of
ammonia in initial gas mixture the films of hexagonal boron nitride were
obtained.
Micro-hardness of the samples was measured by nanoindenter.
The typical loading/unloading curves of 0.94 m thick BCxNy film is
shown in Fig. 14.
Maximal micro-hardness of boron carbonitride films synthesized
from a mixture of TMAB with helium at T = 500 and 700 oC is equal to
34 GPa, and from a mixture of TEAB with nitrogen at 700 oC - H=40
GPa.
62
60000
792
1372
TMAB + NH3
65000
Tdep = 700oC
60000
40000
1244
BCN / Si(100)
2522
-3
PHe = 4x10 Торр
-1
55000
, cm
, cm
-1
50000
30000
-2
P(NH3) = 1,7x10 Torr
20000
50000
45000
0
700 С
0
600 С
0
500 С
40000
-3
P(NH3) = 7x10 Torr
-3
P(NH3) = 4x10 Torr
35000
P(NH3) = 0
10000
30000
500
1000
1500
2000
2500
3000
3500
4000
4500
25000
-1
, cm
а
-3
TEAB + N2 (4x10 Torr)
0,9
IB-C/( IB-C + IB-N)
0,9
0,8
0,7
0,6
0,5
0,4
1000
1500
2000
,cm
1,0
1,0
IB-C/( IB-C + IB-N)
500
b
0,3
0,8
2500
3000
3500
4000
-1
TEAB + NH3
T = 700oC
0,7
0,6
0,5
0,4
0,3
0,2
0,2
0,1
0,1
0,0
0,0
500
550
600
650
0,000 0,004 0,008 0,012 0,016 0,020 0,024 0,028 0,032
700
PNH3, Torr
o
Tdeposition, C
d
c
-3
TEAB + N2 (4x10 Torr)
40
35
H, GPa
H, GPa
40
35
30
TEAB + NH3
o
T = 700 C
30
25
20
15
25
10
20
500
550
600
650
700
o
Tdeposition, C
e
0,000 0,004 0,008 0,012 0,016 0,020 0,024 0,028 0,032
PNH3, Torr
f
Fig. 12. The IR spectra of BCxNy films synthesized from a mixtures of
TMAB+NH3 (a), TMAB+He (b). Dependence of relative content of BC bonds in films (c, d) and hardness (e, f) on growth conditions.
63
1000
62,25-1,490B4C (303)
66,70-1,401B4C (220)
68,95-1,361
72,30-1,306h-BN (104)
58,10-1,586h-BN (103)
53,20-1,720B4C (205)
?
MC-80
41,75-2,162h-BN (100)
44,35-2,041h-BN (101)
?
23,55-3,774B4C (012)
13,40-6,602
16,50-5,368
19,00-4,667B4C (101)
Intensity
Intensity (a.u.)
10000
BCN/Si
Si
100
10
20
30
40
50
2-theta
60
70
80
Fig. 13. The X-ray diffraction pattern of the BCxNy film synthesized
from TMAB + NH3 mixture (PNH3 = 4·10-3 Torr)
Fig. 14. The typical loading/unloading curves of 0.94 m thick BCxNy
film.
These values exceed data given in the literature data (9-14) for
hexagonal phase BCxNy. Lower hardness is exhibited by the films
obtained from a mixture of TMAB (or TEAB) with ammonia, H = 10-15
GPa. The values of Young’s modulus, which characterizes the elasticity
of the films are 226 and 115 GPa for the films synthesized from TMAB
+ He and TMAB + NH3, respectively. There is correlation between
relative content of B-C bonds (IB-C/IB-C+IB-N) and hardness values. Rise
of deposition temperature leads to increase of both carbon content and
hardness values of the films (Fig. 12c, e). Addition of ammonia to initial
64
gas mixture leads to a decrease of carbon concentration and hardness of
BCxNy material (Fig. 12d, f).
Conclusions
So, hard nanocrystaline films of SiCxNy (H ~ 28 GPa) prepared by
RPECVD using HMDS with mixture of ammonia and helium possesed a
very complex bonding structure. Analysis of results obtaned by
spectroscopic methods such as IR spectroscopy, AES and XPS showed
the presence of chemical bonding among Si, N, and C elements. Thus, in
these films SiC compound was not disclosed but component with
binding energy of ~ 101.0 eV indicates to the existence of
polysubstituted tetrahedrons (CnSiN4-n) due to partial replacement of N
atoms in Si-N network by C atoms. According to data of XRD-SR, HREM,
and SAED the formation of the solid substitution solution SiCxNy occurs,
having lattice parameters close to those of the standard phase -Si3N4 in
which a part of silicon atoms is substituted by carbon atoms. The analysis of
structural, optical and mechanical properties of these films indicates
possibility for applications as wide band gap materials, hard protective
coatings, and transparent layers in wide region of visible and far infrared
region spectra.
The superhard nanocrystalline films of boron carbon nitride were
synthesized by low pressure chemical vapor deposition. Trimethylamine
borane and triethylamine borane complexes were used as the singlesource precursors. It was determined that chemical and phase
composition of films depends on growth conditions: deposition
temperature and content of initial gas mixture. Hardness of the films
correlates with content of B-C bonds in material. BCxNy films with the
maximal microhardness of 40 GPa was synthesized.
Acknowledgments
The present work was supported by RFBR grant N 06-03-32713,
Interdisciplinary Project of SB RAS N 67, Grant from the Presidium of
RAS N 8.14 and President of RF N NSh-4419.2006.3.
References
1. S.Boughaba, G.I.Sproule, J.P.McCaffrey et al, Thin Solid Films, 402,
99 (2002)
2. I.V.Afanasyev-Charkin, M.Nastasi, NIM, B, 206, 736 (2003)
65
3. A.Bendeddouche, J.Appl.Phys. 81, 6147, (1997)
4. A.Badzian, J. Am. Ceram. Soc., 85, 16, (2002)
5. N.I.Fainer, Yu.M.Rumyantsev, A.N.Golubenko, M.L.Kosinova,
F.A.Kuznetsov, J.Crys. Growth., 248C, 175, (2003)
6. X.M He, T.N.Taylor, R.S.Lillard, et al, J.Phys.:Condens.Matter, 12,
L591 (2000)
7. JCPDS Int. Center for Diffraction Data, 1988, USA, 41, card N 360
8. N.I.Fainer, E.A.Maximovskii, Yu.M.Rumyantsev, M.L.Kosinova,
F.A.Kuznetsov, NIMA, 470, 193, (2001)
9. M.C. Polo, E. Martinez, J. Esteve, and J.L. Andujar. Diamond Relat.
Mater. 7, 376 (1998)
10. T. Nasegava, K. Yamomoto, and Y. Kakudate. Diamond Relat.
Mater. 11, 1290 (2002)
11. M Dinescu, A. Perrone, et.al. Appl. Surf. Sci. 127-129, 692 (1998)
12. Z.X. Cao, and H. Oechsner. J. Appl. Phys. 93, 1186 (2003)
13. E.Byon, J.-R.Kim et al. Surf. Coat. Tech. 169-170, 340 (2003)
14. S.Stockel, K.Weise, D.Dietrich, T.Thamm, et al., Thin Solid Films.
420-421, 465 (2002)
15. S.Kurooka, T.Ikeda, M.Suzuki, and A.Tanaka. Diamond Relat.
Mater. 12, 1122 (2003)
16. X. Jiang, J. Philip, W.J. Zhang, P. Hess, and S. Matsumoto. J. Appl.
Phys. 93, 1515 (2003)
17. M.L. Kosinova, N.I. Fainer, et al. in Chemical Vapor Deposition/
2003, M.Allendorf and, Editors, 2003-08, p. 709, Electrochemical
Society Proceedings Series, Pennington, NJ (2003)
18. M.Kawaguchi. Advan. Mater. 9, 615 (1997)
66