ISSN 1063-7397, Russian Microelectronics, 2006, Vol. 35, No. 5, pp. 304–309. © Pleiades Publishing, Inc., 2006.
Original Russian Text © V.D. Popov, G.A. Protopopov, 2006, published in Mikroelektronika, 2006, Vol. 35, No. 5, pp. 355–361.
A silicon dioxide (SiO
) ﬁlm is a constituent part
that determines to a large extent the reliability and radi-
ation hardness of planar devices and circuits, particu-
larly ones made in metal–oxide–semiconductor (MOS)
technology. It has been found that screening of MOS
circuits for oxide defects can be done by gamma irradi-
ation followed by thermal annealing, taking place
before dicing [1–3] or after packaging . This proce-
dure is efﬁcient, easily controllable, repeatable, and
fully compatible with MOS technology. It enables both
point and macroscopic oxide defects to be detected .
If the conditions of irradiation and annealing are set
properly, the treatment does not damage or contaminate
the materials and in fact makes MOS circuits more reli-
able, as evinced in higher yields [1, 2, 4].
At the same time, there is some uncertainty over the
extent to which gamma irradiation and thermal anneal-
ing affect the stability of the atomic system of oxide
ﬁlms. As is well known, the state of an atomic system
can be described by its entropy, which, like energy, is
uniquely determined for each state and provides a
means to ﬁnd the probabilities of states.
This paper presents a theoretical investigation into
how gamma irradiation and subsequent thermal anneal-
ing change the entropy of the atomic system of a silicon
dioxide ﬁlm on silicon.
2. STRUCTURE OF A SiO
FILM ON Si
Structurally, silicon dioxide displays a very low
degree of symmetry and only a short-range order [6, 7].
The ﬂexibility of Si–O bonds controls formation of
defects, i.e., local disturbances of the short-range order
associated with a
tetrahedron. Defects in
ﬁlms may be classiﬁed as being either process-induced
or stress-induced .
A silicon dioxide ﬁlm on silicon experiences stress
due to the thermal-expansion mismatch between the
two materials, for oxide growth or deposition takes
place at a high temperature. As a result, a SiO
ture is subject to deformation, with the SiO
the Si subsurface region being compressed and
stretched, respectively . Structural differences
between the dielectric and the semiconductor can also
contribute to the stress .
Once a SiO
/Si structure has been cooled, the
atomic system becomes ﬁxed in a stress-induced non-
equilibrium state with strained Si–O bonds, i.e., ones
that exist on a scale different from the lattice spacing
and/or are oriented at an angle other than the optimal
one. Many defects are therefore likely to arise by break-
ing of the strained bonds. Thus, individual atoms occur
minima of free energy, being in metastable
A major difference of amorphous silicon dioxide
from its crystalline form is the dispersion of tetrahedral
and dihedral angles, as illustrated in Fig. 1. Taken as
random variables, the angles may be approximately
described by the normal distribution
Effect of Ionizing Irradiation and Thermal Annealing
on the Entropy of the Atomic System of a SiO
V. D. Popov and G. A. Protopopov
Moscow Engineering Physics Institute (State University), Moscow, Russia
Received November 25, 2005
—A theoretical investigation is presented into how gamma irradiation and subsequent thermal anneal-
ing change the entropy of the atomic system of a SiO
ﬁlm on Si.
PACS numbers: 81.40.Wx