1063-7397/04/3302- © 2004 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 33, No. 2, 2004, pp. 116–119. Translated from Mikroelektronika, Vol. 33, No. 2, 2004, pp. 148–152.
Original Russian Text Copyright © 2004 by Obolenskii.
Gettering is a very useful method for improving the
electrical properties of active layers, and many getter-
ing mechanisms have been identiﬁed. However, it is not
yet clear what causes the long-range action of ion-beam
gettering, which is detected at depths exceeding the ion
range by one or two orders of magnitude. The long-
range action has been ascribed to radiation-enhanced
diffusion, the inﬂuence of hydrogen complexes, or the
propagation of elastic waves [1, 2]. With respect to the
last model, it might be wise to assess the sensitivity of
semiconductor structures to elastic waves generated by
other agents, such as laser radiation absorbed by the
metallization pattern on the chip surface.
Gettering is intimately linked to the modiﬁcation of
lattice imperfections . It has been demonstrated that
ion-beam gettering improves the radiation hardness of
GaAs metal–semiconductor ﬁeld-effect transistors
(MESFETs) . It is now of interest to investigate get-
high-energy particulate irradiation
producing a large number of defects. This also applies
to laser long-range gettering.
With submicrometer feature sizes, lattice imperfec-
tions are strongly dependent on both the process tech-
nology and the shape of contact pads; this is particu-
larly true of chips with nanometer pads. Laser irradia-
tion has been shown to provide energy deposition
localized near metal edges . This ﬁnding offers a
way to independently determine the energy threshold of
Below we present a comparative experimental study
of the ion-beam and the laser long-range gettering of
GaAs MESFETs. Some of the MESFETs were preirra-
diated with high-energy neutrons.
The experiment was conducted on conventional and
V-groove GaAs MESFETs  with channel lengths of
0.5 and 0.1
m, respectively. A 1.06-
laser was employed, the photon energy being less than
the energy gap of GaAs.
The conventional MESFETs were made with or
without a metal ﬁlm on the back side of the substrate.
The ﬁlm thickness was such as to ensure total conver-
sion of a laser pulse into an acoustic wave. Without the
ﬁlm, laser radiation passed freely through the substrate
and was absorbed by metal pads on the front side, thus
heating the active region.
The V-groove MESFETs had a gate edge radius in
the range 10–15 nm. With back-side laser irradiation,
they experienced localized energy deposition within
50–100 nm from the edge, owing to diffraction . The
energy threshold of modiﬁcation was conveniently
determined with normally off MESFETs, whose cur-
rent–voltage characteristic is known to display a seg-
ment of negative differential conductance (NDC). The
reasons for this behavior and related high-frequency
oscillation are discussed elsewhere .
Prior to dicing, some wafers were thinned to 100
and irradiated with 90-keV Ar ions to a dose of
at an ion current density less than 0.5
the wafer temperature being close to room temperature.
The other wafers, with or without a back-side Au ﬁlm,
were subjected to front- or back-side pulsed laser irra-
diation of pulse width 10 ns, energy 30 mJ, and repeti-
tion period 1 min; the spot diameter was about 1 mm.
Each specimen had an area of
one MESFET. Some of the V-groove MESFETs were
treated with neutrons of mean energy 1 MeV to ﬂu-
ences ranging from
before laser irra-
The performance of irradiated MESFETs was eval-
uated from current–voltage and capacitance–voltage
characteristics. These were measured with the L2-56
recorder and the E7-12 capacitance meter, respectively.
Comparison between the Ion-Beam and the Laser Long-Range
Gettering of GaAs MESFETs
S. V. Obolenskii
Nizhni Novgorod State University, Nizhni Novgorod, Russia
Received April 28, 2003
—A comparative experimental study is presented of the ion-beam and the laser long-range gettering
in GaAs MESFETs using an n
structure. It is shown that the similarity of the two processes results from the
fact that both of them depend on the modiﬁcation of the interfaces by elastic waves generated in the structure.
It is demonstrated that the laser irradiation of quasi-ballistic MESFETs pretreated with neutrons allows one to
create a system of radiation-induced channel defects that improves the performance of the device.
ON ADVANCED GaAs FETs