ISSN 0012-5008, Doklady Chemistry, 2008, Vol. 421, Part 2, pp. 194–196. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © R.G. Mirskov, V.I. Rakhlin, S.N. Adamovich, M.G. Voronkov, 2008, published in Doklady Akademii Nauk, 2008, Vol. 421, No. 6, pp. 777–778.
CHEMISTRY
High-Purity Alkoxychlorosilanes as New Precursors
for Precipitation of Silica
R. G. Mirskov, V. I. Rakhlin, S. N. Adamovich, and Academician M. G. Voronkov
Received April 29, 2008
DOI: 10.1134/S0012500808080077
Organosilicon precursors containing Si–O–C,
Si−O–Si, Si–O–M (M = B, P, Sb, etc.), Si–N–Si, and lowing high-purity alkoxychlorosilanes: trimethoxy-
chlorosilane (CH O) SiCl (I), dimethoxydichlorosilane
To verify this assumption, we synthesized the fol-
Si−N–C groups were proposed in our previous study
1] for plasma-chemical deposition of nanosized silica
3
3
(
(
CH O) SiCl (II), methoxytrichlorosilane CH OSiCl
[
3 2 2 3 3
III), triethoxychlorosilane (C H O) SiCl (IV),
2 5 3
layers and M atom–doped silica and silicon nitride and
carbonitride layers, which are widely used in the design
of modern micro- and optoelectronic devices. They all
are environmentally safe, readily available volatile liq-
uids and may replace the traditional precursors, which
are toxic, explosive, and expensive gases (silane, dibo-
rane, phosphine, etc.), without loss of quality.
diethoxydichlorosilane (C H O) SiCl (V), and ethox-
2
5
2
2
ytrichlorosilane C H OSiCl (VI).
2
5
3
It is known that alkoxychlorosilanes are usually syn-
thesized by the reaction of silicon tetrachloride with
alcohols [3]. We used this method to prepare com-
pounds II, III, V, and VI in yields of up to 70%. How-
ever, for the synthesis of trialkoxychlorosilanes I and
IV in up to 92% yields, we proposed a method based on
the reaction of tetramethoxy- or tetraethoxysilane with
acetyl chloride in the presence of aluminum or zinc
chloride
Previously it was shown that decomposition of high-
purity heptamethylchlorocyclotetrasiloxane (HMCS)
in a high-frequency (HF) electric discharge plasma
gives rise to nanosized layers of chlorine-doped silica
on the surface of single crystalline silicon [2]. Electro-
physical properties of the resulting coatings were
higher than for coatings deposited from traditional pre-
cursors, namely, tetramethoxy- and tetraethoxysilane.
(RO) Si + ClCOMe
(RO) SiCl + ROCOMe,
3
4
R = CH (I), C H (IV).
3
2
5
Decomposition of alkoxytrichlorosilanes I–VI in an
The introduction of electronegative chlorine atoms into HF discharge plasma in an oxygen atmosphere gave
SiO layers during their formation counterbalances the SiO layers with thickness 0.1–0.4 µm, which were
2
2
fixed positive charge and improves the properties of the studied by Auger and IR spectroscopy. The layers
obtained from precursors I, IV, and V had the following
elemental composition (wt %) Si, 33–33.5; C, 0.5–1; O,
66; Cl, 0–0.1. Coatings of alkoxychlorosilanes II, III,
and VI have the composition (wt %) Si, 33; O, 66; Cl,
Si–SiO interface. However, due to a low saturated
2
vapor pressure of HMCS, the growth rate of SiO layers
2
–
1
was relatively low (0.063–0.14 µm h ).
This drawback and the relatively low yield of the up to 1.0 (no carbon). The IR spectra of SiO layers
2
–
1
exhibit absorption bands at 1070–1080 cm (Si–O–Si
stretching vibrations) typical of amorphous silica and
precursor during its synthesis, which hamper extensive
practical use of HMCS, can be easily eliminated. We
found that HMCS can be replaced by more readily
available volatile alkoxychlorosilanes (RO)4 – nSiCln,
where R = Me, Et; n = 1–3. By varying the ratio of Si
and Cl atoms in the initial alkoxychlorosilanes (from 1 : 1
to 1 : 3), it is possible to affect the magnitude and effi-
ciency of the mobile charge in silica layers formed from
them.
–
1
weak bands at 740 and 2350 cm (Si–C and Si–H
stretching vibrations, respectively). In the IR spectra of
the coatings after heat treatment at 1000°ë in an oxy-
gen or nitrogen environment, the major band shifts to
–1
–1
1
080–1090 cm and the bands at 747 and 2350 cm
disappear.
The table gives the deposition parameters and elec-
trophysical properties of SiO layers obtained from
2
alkoxychlorosilanes I–VI, namely, the pressure of the
vapor–gas mixture (VGM) P, the contents of alkoxy-
chlorosilanes in the VGM (%), the layer deposition rate
V, the relative dielectric permittivity Σ, the refractive
index n, and the dielectric strength of the coatings Es.
Favorskii Institute of Chemistry, Siberian Branch,
Russian Academy of Sciences, ul. Favorskogo 1,
Irkutsk, 664033 Russia
1
94