ISSN 10637397, Russian Microelectronics, 2015, Vol. 44, No. 1, pp. 33–39. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © A.A. Pechenkin, D.V. Savchenkov, O.B. Mavritskii, A.I. Chumakov, D.V. Bobrovskii, 2015, published in Mikroelektronika, 2015, Vol. 44, No. 1, pp. 41–48.
Currently, when performing the experimental stud
ies and tests of microelectronic devices for modeling
singleevent radiation effects under the influence of
heavy ions, tests based on focused picosecond laser
irradiation are widely used [1–3].
The multilayer metallization and the technology of
flipchip crystals in modern VLSIs substantially
restrict the application of classical frontside method of
laser irradiation – from the devicelayer side of IC.
Therefore, the alternative methods based on the laser
irradiation from the substrate side, i.e., through the
substrate, are potentially interesting . In this article,
we propose a modified local laser irradiation tech
nique [4, 5] to evaluate the sensitivity parameters of
CMOS LSI ICs to single event latchup effect, caused
by heavy ions. This technique is applicable for laser
irradiation from the back side of IC crystal.
2. OPTICAL FOCUSING ON A DEVICE LAYER
FROM THE BACK SUBSTRATE SIDE
The possibility to irradiate semiconductor struc
tures through the silicon substrate is based on the fact
that the laser radiation with a wavelength of 1064 nm
has relatively weak absorption in silicon (Fig. 1). For
example, even for silicon substrates with a thickness of
m, optical losses are only severalfold. When irra
diating the IC with a thinner substrate (200–300
there is the possibility to use shorter wavelengths .
Upon the irradiation through a silicon substrate of
IC, the plane of sharp focusing of the laser radiation is
displaced into the depth of the crystal due to the
refraction effect at the air–silicon interface (Fig. 2). In
silicon substrate the diameter of Gaussian beam waist
is the same as in vacuum, but the focal length (the
length of the beam region, where diameter is close to
that of beam waist) noticeably increases. This allows us
to modify the local laser irradiation technique [4, 5] to
make it useful for backside IC crystal irradiation.
The local laser irradiation technique application
requires providing the predetermined variation of the
effective diameter of the laser radiation spot in the sen
sitive region . The conventional way of varying the
laser radiation diameter is to move the IC crystal along
laser beam axis relative to the plane of sharp beam
focusing. Moreover, when irradiating the backside, the
refraction of the optical radiation at the air–silicon
boundary takes place. The interrelation of the effective
spot diameter with the value of the displacement along
laser beam axis can be established in the Gaussian laser
beam approximation taking into account that the
beam divergence angle changes at the airsilicon
boundary due to the refraction. Fig. 3 shows an exam
ple of the focused laser beam diameter variation with
the distance from the air–silicon boundary for two val
ues of numerical aperture
of the focusing optics.
Calculated values of minimal waist diameter
presented. Similar estimations for typical laser sources
revealed that their Gaussianbeam focal length value
in silicon is more than 10
m, and therefore one can
assume with sufficient accuracy that for most LSI ICs
their sensitive device layers are located just near the
opposite crystal surface. Thus, the problem of proper
focusing can be reduced to obtaining of laser beam
waist location on the opposite substrate surface just
near the deepest metallization layer.
Consequently, an important aspect, which provides
the correctness of applying the technique, is an exact
determination of the siliconsubstrate thickness. It is
Evaluation of Sensitivity Parameters for Single Event Latchup Effect
in CMOS LSI ICs by Pulsed Laser Backside Irradiation Tests
A. A. Pechenkin, D. V. Savchenkov, O. B. Mavritskii, A. I. Chumakov, and D. V. Bobrovskii
National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia
JSC Specialized Electronic Systems (SPELS), Moscow, Russia
email: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Received May 25, 2014
—The results of computationexperimental modeling of singleevent latchup effects under the laser
radiation focused on the IC crystal backside—the substrate side—are presented. Possibilities of applying the
technique of local laser irradiation to evaluate equivalent linear energy transfer of heavy ions in the case of the
laser irradiation from the substrate side of IC crystal are analyzed. The experimental results obtained using
the pulsed laser installation and accelerators of charged particles for a series of modern LSI ICs are compared.