ISSN 10637397, Russian Microelectronics, 2015, Vol. 44, No. 1, pp. 54–59. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © A.V. Sogoyan, V.A. Polunin, 2015, published in Mikroelektronika, 2015, Vol. 44, No. 1, pp. 65–70.
The degradation of the undergate dielectric in
MOS structures is one of the main factors determining
the service life of modern CMOS VLSIs. It can be
caused by electric loads (the injection of hot carriers
from the substrate and highfield injection) and by the
effect of the ionizing radiation (IR), particularly of
heavy charged particles. The influence of the effect of
heavy charged particles on the characteristics of thin
oxide layer was repeatedly observed experimentally
[1–4]. For example, the authors of  established the
substantial influence of the preliminary effect of heavy
charged particles on the electric strength of oxide.
Oxide films 2.2–3.3 nm thick, which were irradiated
by heavy charged particles, demonstrated an increase
in leakage currents and lowering the breakdown volt
ages. The effect is enhanced with an increase in the
linear energy losses (LEL) of heavy charged particles
and a decrease in the dielectric thickness. The irradia
tion of a dielectric 3.3 nm thick by Au ions led to the
lowering of the critical charge by two orders of magni
tude. The authors of  observed a decrease in the reli
ability characteristics of oxide (shortening the time
before the breakdown during electric stress
the effect of the Si, Br, I, and Au ions. A decrease in
was also mentioned in the devices, in which no sub
stantial leakage immediately after the irradiation was
observed. This result corresponds to the evident
assumption that the degradation of oxides is caused by
structural defects generated during the passage of
heavy charged particles.
The authors of  experimentally investigated the
appearance of leakage currents in the oxide of MOS
structures with a floating gate. The experimental
results indicated the appearance of permanent leakage
channels of undergate oxide due to the effect of ions.
The magnitude of ther leakage correlated with the
LEL of ions.
Thus, the available experimental data indicate that
the effect of heavy charged particles leads to lowering
the reliability characteristics of thin (thinner than
10 nm) dielectrics and the appearance of leakage cur
rents. The effects caused by the influence of heavy
charged particles turn out to be latent, manifesting
themselves in a form of a device fault somewhat after
In general, the defect formation in semiconductors
and dielectrics during the passage of heavy charged
particles is caused by the effect of primary knocked
out atoms (PKAs) and the thermal modification of the
structure near the track axis [5, 6].
The formation of separate structural defects by
PKAs can be analyzed using a numerical model .
Figure 1 shows the computed distributions of the
number of defects in an oxide film 10 nm thick (the
probability of generation of the number of defects
exceeding the specified magnitude per primary ion).
The distributions are normalized allowing for events
corresponding to the defect generation. Figure 2
shows the radial density distributions of defects gener
ated in the
layer during the ion passage. The pre
sented results of the calculation show that the average
density of a PKAcaused defect rapidly descends
remote from the track axis. At the same time, the anal
ysis shows that when implementing the events with
considerable damage, the formation of defect clusters
occurs according to traditional notions.
A Model for the Formation of Leakage Currents in the Dielectrics
of MOS Structures under the Effect of Heavy Charged Particles
A. V. Sogoyan and V. A. Polunin
National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia
Institute of Extreme Applied Electronics, National Research Nuclear University MEPhI
(Moscow Engineering Physics Institute), Moscow, Russia
email: email@example.com, firstname.lastname@example.org
Received August 11, 2014
—The degradation of the undergate dielectric of MOS structures belongs to the main factors deter
mining the service life of modern CMOS VLSIs. The experimental data indicate that the effect of heavy
charged particles leads to lowering the reliability characteristics of thin (thinner than 10 nm) dielectrics and
the appearance of leakage currents. As this takes place, the effects caused by the effect of heavy charged par
ticles turn out to be latent. In the article, a model of the formation of the leakage current of the dielectric
caused by the effect of heavy charged particles is proposed. The model is based on the solution of the set of
kinetic equations and makes it possible to overcome a series of limitations of the known percolation approach.