ARTICLE IN PRESS
Physica B 404 (2009) 5153–5155
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Physica B
Strain relaxation mechanism in the Si-SiO2 system and its influence on the
interface properties
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a
a
a
a
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D. Kropman a, , E. Mellikov , A. Opik , K. Lott , O. Volobueva , T. Ka¨rner , I. Heinmaa ,
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T. Laas d, A. Medvid e
a Tallinn University of Technology, 5 Ehitajate tee, 12618 Mustamae, Tallinn, Estonia
b Tartu University, Estonia
c Institute of Chemical Physics and Biophysics, Estonia
d Tallinn University, Estonia
e Riga Technical University, Latvia
a b s t r a c t
The results of the investigation of stresses relaxation by strain by means of EPR spectra, IR absorption
spectra, SEM and samples deflection are presented. It has been shown that stresses relaxation
mechanism depended on the oxidation condition: temperature, cooling rate, oxide thickness. In the Si-
SiO2-Si3N4 system the stresses relaxation by the strain occur due to the opposite sign of the thermal
expansion coefficient of SiO2 and Si3N4 on Si. Laser irradiation allows to modify the system stresses.
& 2009 Elsevier B.V. All rights reserved.
1. Introduction
nm, 10 MW/cm2) were performed after oxidation before Al
evaporation.
It is known that internal mechanical stresses due to the
differences in the thermal expansion coefficient between films
and substrates and lattices mismatch appear in the Si-SiO2 system
during the process of its formation and that point defects
generation and redistribution reduce partially the surface strain.
However, no investigation of this process on the atomic scale has
been carried out so far. The purpose of the present work is to
investigate the strain relaxation mechanism in the Si-SiO2 system
by means of EPR, IR absorption spectroscopy, scanning electron
microscopy (SEM) and samples bending measurements.
3. Results and discussion
It has been found that samples bending increases or decreases
simultaneously with EPR signal intensity depending on the
oxidation temperature, oxidation time and cooling rate (Fig. 1).
It may be due to the relaxation of stresses by the strain
accompanied by the point defects gettering and by creation of
point defects by the stresses [1]. It has been found that in case of a
lower oxidation temperature (1100 1C) the deflection of the
samples decreases with an increase of the Pa centers EPR signal
intensity (E0 centers in SiO2 and vacancy complexes in Si) while at
a higher oxidation temperature (1200 1C) the deflection of the
samples and EPR signal intensity increase simultaneously [2]. The
revealed differences in the strain dependence on the point defects
density (type) at different oxidation temperature allow to suggest
that relaxation mechanism of the internal mechanical stresses
(IMS) is different. During oxidation at 1100 1C oxygen diffuses
through the oxide to the interface where oxidation happens which
is associated with a volume expansion. Part of the volume is
released by injection of Si self-interstitials into the Si. At 1200 1C
diffusion of Si from the interface into the oxide occurs and the
oxidation reaction happens in the oxide. This process is associated
with vacancy injection into the Si. The decrease of the deflection
with an increase of the vacancies type point defects EPR signal
intensity indicates that self-interstitial Si atoms injection are
2. Experimental
Si n-type with 15
used. The oxides were thermally grown in dry oxygen at 1100–
1200 1C. The SiO2 film thickness varied from 0.2 m to about
0.5 m. The density of point defects was varied by varying the
O cm resistivity and (111) orientation was
m
m
cooling rate of the samples (3 of 25 1C/s). The EPR spectra were
taken at 115 K by an X-band ESR 231 spectrometer. To evaluate
the influence of the defects structure on the stresses in SiO2, the
measurements of SiO2 IR absorption spectra were carried out. The
strain in the Si-SiO2 system were investigated by means of SEM
and samples bending measurements. Laser irradiation (
l ¼ 520
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Corresponding author.
0921-4526/$ - see front matter & 2009 Elsevier B.V. All rights reserved.