N-Substituted hexamethyldisilazanes as new substances for the synthesis of functional films in the system Si-Ge-C-N-H

Article abstract of DOI:10.1134/S1070363211120140

N-Organylbis(trimethylsilyl)amines of the general formula RN(SiMe ₃)₂ (R = Me₃Si, Et₃Ge) were synthesized by reaction of sodium bis(trimethylsilyl)amide with the corresponding trialkylsilyl(germyl) halide. Their IR, UV, and ₁H, ₁₃C, and ₂₉Si NMR spectra were studied, and saturated vapor pressures and thermal stabilities were determined. The possibility of using the RN(SiMe₃)₂ compounds as precursors in chemical vapor deposition of films with specified composition was estimated by thermodynamic modeling. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S1070363211120140

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 12, pp. 2501–2505. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.V. Sysoev, L.D. Nikulina, A.O. Kolontaeva, M.L. Kosinova, A.A. Titov, V.I. Rakhlin, I.P. Tsyrendorzhieva, A.V. Lis, M.G. Voronkov,
2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 12, pp. 2055–2059.
N-Substituted Hexamethyldisilazanes as New Substances
for the Synthesis of Functional Films
in the System Si–Ge–C–N–H
S. V. Sysoeva, L. D. Nikulinaa, A. O. Kolontaevaa, M. L. Kosinovaa, A. A. Titova,
V. I. Rakhlinb, I. P. Tsyrendorzhievab, A. V. Lisb, and M. G. Voronkovb
a Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
e-mail: marina@niic.nsc.ru
b Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
Received July 7, 2011
Abstract—N-Organylbis(trimethylsilyl)amines of the general formula RN(SiMe3)2 (R = Me3Si, Et3Ge) were
synthesized by reaction of sodium bis(trimethylsilyl)amide with the corresponding trialkylsilyl(germyl) halide.
1
Their IR, UV, and H, 13C, and 29Si NMR spectra were studied, and saturated vapor pressures and thermal
stabilities were determined. The possibility of using the RN(SiMe3)2 compounds as precursors in chemical
vapor deposition of films with specified composition was estimated by thermodynamic modeling.
DOI: 10.1134/S1070363211120140
Organosilicon compounds are promising as starting
materials for the preparation of substances used in
various fields of science and technics. An example of
their application in microelectronics is their use as dry
vacuum resists [1–3]. Some organosilicon compounds
are used to obtain ultrathin aligning films for the
manufacture of display devices [4]. Much attention is
given to the synthesis of volatile organosilicon
compounds for the preparation of films and coatings
based on silicon nitride, carbide, and carbonitride
(SiCxNy) by plasma-enhanced chemical vapor deposi-
tion (PECVD) [5–8]; SiCxNy films possessing various
sets of functional properties were obtained. Introduc-
tion of germanium atoms into molecules of organo-
silicon compounds could give rise to new functional
materials with specific optical and electric properties,
as well as to biologically active substances [9, 10].
In the present work we examined specificity of the
synthesis of N-organylbis(trimethylsilyl)amines of the
general formula RN(SiMe3)2 (R = Me3Si, Et3Ge) and
their physicochemical parameters as precursors for the
preparation of thin-layer structures by vapor deposi-
tion. The target compounds were synthesized by reac-
tion of sodium bis(trimethylsilyl)amide with tri-
methylsilyl or triethylgermyl halide in toluene. The
products were colorless gel-like substances with a
specific odor, which readily liquefied on heating. Their
yield and purity depended on the initial organyl halide
and solvent nature. The yield of I was 82%, and the
yield of II was 77%.
PhCH=CH2
(Me3Si)2NH + Na
(Me3Si)2NNa,
(Me3Si)2NNa + R3MHlg → (Me3Si)2NMR3,
R3M = Me3Si (I), Et3Ge (II), Et3Sn (III).
We previously studied reactions of N,N-disub-
stituted carboxylic acid amides with iodotrimethyl-
silane and obtained
a series of aminosilanes:
The IR spectra of compounds I and II are given in
Table 1. Absorption bands were assigned according to
[12, 13]. Bands typical of vibrations of the Si–N–Si
fragment in disilazanes were observed in the region
Me3SiNEt2, Me3SiNNAll, Me3SiNHPh. These com-
pounds may be recommended for use as pre-cursors of
silicon carbonitride films in chemical vapor deposition
(CVD) processes [11].
2501

2502
SYSOEV et al.
ln P
λ, nm
1000/T
Fig. 2. Temperature dependences of saturated vapor pressure
of (1) N(SiMe3)3 and (2, 3) Et3GeN(SiMe3)2.
Fig. 1. UV spectra of compounds (1) I and (2) II.
837–962 cm–1. Strong bands in the regions 1252–1257
and 1354–1460 cm–1 resulted from stretching and
bending vibrations of the Si–C bonds. Stretching vibra-
tions of the C–H bonds gave rise to absorption at
2874–2956 cm–1. Compounds I and II displayed in the
UV spectra absorption maxima at λ 200–270 nm (Fig. 1).
The temperature dependences of saturated vapor
pressure of compounds I and II were determined by
the static method with the aid of a glass membrane
pressure gauge [14] (Fig. 2). Processing of the
experimental data with the sum of squared normalized
pressure deviations as target function [15] gave
temperature dependences of saturated vapor pressure
in the form ln P = A – B/T, and thermodynamic
parameters of vaporization processes (enthalpy and
entropy of vaporization at the mid temperature in the
examined range) were determined. The results are
collected in Table 2. Compounds I and II turned out to
be fairly stable within the examined temperature range,
as followed from good agreement between the data on
vapor pressure obtained upon heating and cooling. The
plots shown in Fig. 2 allowed us to estimate the
temperature and heat effect of the transition of Et3GeN·
(SiMe3)2 from jellous to liquid state: T = 340±3 K,
ΔH = 15±8 kJ mol–1. Qualitative volatility parameters
of organometallic compounds can be obtained by
integral thermal analysis; the corresponding data are
shown in Fig. 3. It is seen that the temperature of
maximal weight loss for compound II is higher than
for compound I, which is consistent with the obtained
quantitative data on vapor pressure.
Table 1. IR spectra (ν, cm–1) of compounds I and II
Assignment
νasim (CH) in CH3
I
II
2956
2902
2955
2907
2874
νsim (CH) in CH3
νasim (CH2) in CH2CH3
νsim (CH2) in CH2CH3
δ (Si–CH3), δ (Si–CH2–CH3)
1439
1406
1354
1460
1431
1379
1252
1007
962
δasim (CH2) in CH2CH3
ν(Si–C)
1257
918
844
ν(Si–N–Si)
916
879
837
766
679
620
397
758
δwagging (NH) + rocking vibrations
(– CH3) in Si(CH3)x
Thermodynamic modeling provides an efficient
method for the determination of optimal conditions for
chemical vapor deposition (CVD). It makes it possible
to predict the composition of deposited phase
complexes and partial pressures of components of the
equilibrium gas phase upon vide variation of the
698
673
617
575
382
twisting, in-plane,
and out-of-plane
vibrations in amines
vibrations of the M(Ge)–N bond,
composite lattice vibrations
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 12 2011

N-SUBSTITUTED HEXAMETHYLDISILAZANES AS NEW SUBSTANCES
Table 2. Thermodynamic parameters of vaporization of compounds I and II
2503
ln P(Торр) = A – B/T
Temperature,
ΔHvap, kJ mol–1
ΔS°vap, J mol–1 K–1
Compound
°C
А
B
Et3GeN(SiMe3)2
N(SiMe3)3
17.77
18.07
6072
5474
50.5±0.3
45.5±0.2
92.7±0.7
95.1±0.4
50–200
20–178
conditions (temperature, pressure) and compositions of
the initial gas mixture. The calculation procedure is
based on minimization of the ratio of the Gibbs energy
of a flow system to the amount of non-deposited
element (e.g., hydrogen or inert gas), which is
described in detail in [16]. It was believed that a
condensed phase has a constant composition and that
gaseous substances conform to the ideal gas law. As
initial data we used standard thermodynamic
parameters of individual substances: ΔfH°, S°, Cºp =
f(T). Unfortunately, thermodynamic parameters of
ternary compound (silicon carbonitride), germanium
carbide and nitride, and their possible compounds with
hydrogen are unknown. The set of consistent thermo-
dynamic parameters for all compounds was taken the
Electronic Technics Materials Database (Nikolaev
Institute of Inorganic Chemistry, Novosibirsk).
Thus the examined compounds are promising as
precursors for chemical vapor deposition of various
functional thin-layer structures from the viewpoints of
both their physicochemical properties (saturated vapor
pressure, thermal stability) and the possibility for
formation of silicon carbonitride (SiNxCy) over a fairly
wide range of conditions.
EXPERIMENTAL
The concentrations of carbon, hydrogen, nitrogen,
and silicon were determined by burning with the aid of
(a)
DSC, mW mg–1
TG, %
Start: 130.0°C
exo
Thermodynamic modeling of chemical vapor
deposition in the system Si–C–N–H was performed
over a wide temperature range (300–1300 K) at a
pressure of 0.01 to 10 mm using N(SiMe3)3 as initial
compound in a mixture with an inert gas and hydrogen.
Here, the input flows of the precursor and carrier gas
were treated as flows of elements, and an additional
gas flow (He, H2) was assumed to be possible in the
deposition zone.
Temperature, °С
(b)
DSC, mW mg–1
exo
The CVD diagram in Fig. 4 shows temperature
ranges for deposition of different phase complexes
under conditions ensuring thermal decomposition of
the reagent alone or its decomposition in an inert gas.
In the low-temperature region, joint deposition of
silicon carbide and nitride with carbon should be
observed. The process in the presence of hydrogen in
the low-temperature region should result in deposition
of silicon carbide and nitride without impurity of
carbon. Figure 5 shows the CVD diagram in the
system N(SiMe3)3–H2. Increase of the overall pressure
extends temperature range of phase equilibria.
Deposition of silicon nitride may be expected in the
low-temperature process with the use of ammonia.
TG, %
Start: 164.4°С
Temperature, °С
Fig. 3. Thermal analysis of compounds (a) I and (b) II:
(1) TG, (2) DTG, and (3) DSC.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 12 2011

2504
T, K
SYSOEV et al.
T, K
(a)
n(H2)/n[N(SiMe3)3]
n(He)/n[N(SiMe3)3]
T, K
(b)
Fig. 4. CVD diagram of the system N(SiMe3)3–inert gas;
pressure 0.01 mm.
a Thermo Finnigan Flash EA 1112 Series C,H,N
analyzer. The IR spectra (375–7800 cm–1) were
recorded from samples placed between KBr plates on a
Scimitar FTS 2000 (Digilab) spectrometer with Fourier
transform (resolution 1 cm–1). The UV spectra (λ 190–
400 nm) were measured on a Shimadzu UV-3101PC
scanning spectrophotometer from films applied to an
optically transparent quartz support. The refractive
indices were determined by spectrophotometry. The
1H, 13C, and 29Si NMR spectra were recorded on a
Bruker DPX 400 instrument at 400.13, 100.58, and
79.46 MHz, respectively, from solutions in CDCl3
using tetramethylsilane as reference. Thermal analysis
was performed in a helium atmosphere using a Netzsch
STA 409 thermal analyzer. The saturated vapor
pressures were measured by static method with the aid
of a glass membrane pressure gauge [14].
n(H2)/n[N(SiMe3)3]
Fig. 5. Temperature ranges for phase complexes in the
system N(SiMe3)3–H2 at different hydrogen flow rates at a
residual pressure of (a) 1 and (b) 0.01 mm.
%: C 46.19; H 10.98; N 5.38; Si 37.54. C9H27Si3N.
Calculated, %: C 46.28; H 11.65; N 6.00; Si 36.07.
Tris(trimethylsilyl)amine (I). A mixture of 36 g
(0.22 mol) of hexamethyldisilazane and 22 ml of
styrene was added dropwise under stirring to a
suspension of 5.1 g (0.22 mol) of metallic sodium in
250 ml of boiling toluene. The mixture was stirred for
3 h on heating under reflux, 24 g (0.22 mol) of
chlorotrimethylsilane was slowly added, the mixture
was stirred for 4 h under reflux, the solvent was
distilled off, and the precipitate was filtered off.
Vacuum distillation of the filtrate gave 41.6 g (82%) of
compound I with bp 98–100°C (13 mm); published
Triethylgermylbis(trimethylsilyl)amine (II) was
synthesized in a similar way from 31 g (0.19 mol) of
hexamethyldisilazane and 45
g (0.19 mol) of
bromotriethylgermane using 4.4 g (0.19 mol) of
metallic sodium and 20 ml of styrene. Vacuum
distillation gave 47 g (77%) of compound II with bp
100–105°C (2 mm). 1H NMR spectrum, δ, ppm: 0.14 s
(18H, SiCH3), 1.30 q (6H, CH2), 1.11 t (9H, CH3). 13C
NMR spectrum, δC, ppm: 5.65 (SiCH3), 8.60 (CH2),
9.64 (CH2CH3). 29Si NMR spectrum: δSi –2.2 ppm.
Found, %: C 45.73; H 10.61; N 3.68. C12H33GeSi2N.
Calculated, %: C 45.02; H 10.39; N 4.37.
1
data [17]: bp 216°C (760 mm). H NMR spectrum: δ
0.21 ppm, s (27H, CH3). 13C NMR spectrum: δC 5.34
ppm (CH3). 29Si NMR spectrum: δSi 2.34 ppm. Found,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 12 2011

N-SUBSTITUTED HEXAMETHYLDISILAZANES AS NEW SUBSTANCES
2505
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ACKNOWLEDGMENTS
The authors thank N.I. Alferova and I.V. Yushina
(Nikolaev Institute of Inorganic Chemistry,
Novosibirsk) for recording the IR and UV spectra. This
study was performed under financial support by the
Siberian Division of the Russian Academy of Sciences
(integration project no. 97).
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