Specific Features of Structuring of Film-forming Silica Sols
in the Presence of Boric Acid and Four-Arm Polyol
with Hyperbranched Structure
I. V. Smirnova
, T. G. Movchan
, and O. A. Shilova
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia
Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia
Received November 19, 2009
Abstract—Results of a rheological study of colloid systems synthesized by the sol-gel technique are presented.
The method of rotation viscometry was used to examine the effect of boric acid and an organic modifier (polyol
with hyperbranched structure, introduced in various amounts of 0.7 to 2.0 wt %) on structuring processes in
sols based on tetraethoxysilane. Dilatant and thixotropic properties of the systems under study are described.
The range of optimal concentrations of the organic modifier, in which thin hybrid organic-inorganic films are
formed, was found.
OF SYSTEMS AND PROCESSES
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2010, Vol. 83, No. 12, pp. 2128–2134. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.V. Smirnova, T.G. Movchan, O.A. Shilova, 2010, published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 12, pp. 2001–2007.
The sol-gel technique is successfully employed in
microelectronics and optics as a method for deposition
of thin silicate films, sources for diffusion of a number
of doping impurities into materials used in electronics
(silicon, gallium arsenide) [1–10]. As the requirements
to properties of diffusant sources become increasingly
stringent, methods and approaches used in the sol-gel
technology are being improved [1, 3]. For example,
introduction of organic modifiers (polyols with linear
or branched structure), together with an inorganic
doping impurity (H
), enabled an increase in the
critical thickness of silicate films with high content of
boron without deterioration of the surface morphology
and thereby improved the reproducibility of diffusion
parameters, with the diffusion source made nearly
infinite [3, 5, 9, 10].
A number of requirements are imposed on the
properties of films used in the planar technology of
microelectronics: thickness uniformity, continuity or
solidity without breaks and cracks, structural
homogeneity without stratification and crystalline
inclusions, transparency, and possibility of removal in
selective etchants or by ion-plasma etching without
disruption of lower-lying layers.
To satisfy the above requirements, it is primarily
necessary to provide reproducible sol synthesis
conditions. The film-forming sols must be homo-
geneous mobile fluids that form no precipitates, do not
undergo stratification, and possess a necessary
viscosity [3–6, 9].
The time during which sols are suitable for forma-
tion of films satisfying the requirements of the planar
technology of microelectronics is determined, among
other things, by their viscosity [9–12]. The film-
forming properties of sols start to be manifested upon
structuring of a fluid, rather than immediately. Sols
with increased viscosity, close to a transition to a gel,
are unsuitable for formation of high-quality films. At
the same time, use of freshly prepared, yet unaged sols
is also undesirable.
Thus, the viscosity is an important characteristic of
film-forming sols [11–15]. This characteristic is to be
know for reproducible deposition of films with
prescribed thickness and structure in the planar tech-
nology of microelectronics. From the theoretical
standpoint, it is important to determine the con-
centration limit until which organic modifiers can be
introduced into sols without disintegration of the
network of the inorganic polymer formed in sols based
on tetraethoxysilane. Nevertheless, data on the
rheological properties of multicomponent silica sols