ISSN 1063-7397, Russian Microelectronics, 2008, Vol. 37, No. 2, pp. 98–106. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.A. Zhukov, 2008, published in Mikroelektronika, 2008, Vol. 37, No. 2, pp. 111–120.
In the previous part of this study, we proposed a
strategy for achieving ultimate resolution in focused-
ion-beam (FIB) microscopy . It differs from the
well-known FIB technologies in some crucial respects:
(i) It employs a source of
or ions that has
the effective radius
1 nm, the ion-energy spread
eV, and an emitter current of 5 or 0.2 nA,
respectively [2, 3].
(ii) The ion energy at the target is as low as
30 keV in conventional FIB technologies.
The lower value provides an optimal relationship
between diffraction-aberration spot diameter and lat-
eral ion scattering in the target .
(iii) Potential secondary emission of ions and elec-
trons is used instead of kinetic secondary emission as a
means of imaging at the nanometer scale .
(iv) The strategy relies on a chromatic-aberration
correction system based on a combined electromag-
netic mirror .
We have shown that with only chromatic aberration
corrected the ﬁrst three factors acting simultaneously
allow one to obtain a resolution of 1.6 or 1.5 nm for
or ions, respectively .
In the present part, we propose a method for achiev-
ing a similar resolution without chromatic-aberration
correction. A classical theorem of charged-particle
optics states that any aberration of a lens varies as the
size of the lens [7, 8]. The size of an FIB system is
bounded below by two main factors:
(i) The dielectric strength of the insulators that sep-
arate the electrodes having the maximum level of mean
electric-ﬁeld strength for the FIB system concerned ;
(ii) The accuracy of existing lithographic processes
for vacuum micro- or nanoelectronics [9–11].
The ultimate goal of our study is to determine the
minimum possible size of an FIB system.
The aim of this paper is to calculate the aberrations
and resolution of an FIB system having the minimum
possible size as governed by the two factors. As we
shall see, the resolution differs little from that obtained
with the chromatic-aberration correction system .
Note also that the FIB considered is more properly
called a microFIB.
FORMULATION OF THE PROBLEM
As the basis of the ion-optical system (IOS) of the
micro FIB, let us accept a four-electrode emission lens
considered in the previous article . Note that, in the
previous article , under the conditions of the use of
the aberration corrector, an angular aperture at the tar-
get was determined by an oriﬁce in a special diaphragm
placed outside the four-electrode lens (inside the aber-
ration corrector). In the case considered in this article,
in the absence of the corrector, we should add this spe-
cial aperture diaphragm having the target potential to
the four-electrode (three-aperture) lens, effectively
Achieving Sub-1.6-nm Resolutions of a Low-Voltage Microscopic
Focused-Ion-Beam System Not Involving Aberration Correction
V. A. Zhukov
St. Petersburg Institute for Informatics and Automation, Russian Academy of Sciences, St. Petersburg, Russia
Received July 2, 2007
—The ﬁnal, second, part is presented of an investigation into possible methods of achieving the ulti-
mate resolution for focused-ion-beam (FIB) microscopes. Our strategy differs from the well-known FIB tech-
nologies in the following respects: (i) It employs an advanced ion source of effective radius
nm. (ii) The ion
energy at the target is as low as –300 eV. (iii) Potential secondary emission of ions and electrons is used as a
means of imaging at the nanometer scale. The version in part 1 relies on a chromatic-aberration correction sys-
tem based on a combined electromagnetic mirror. As an alternative, we here propose reducing the ion-optical
system to a scale of tens of micrometers. It is shown by computer simulation that the resolution thus obtained
should be as good as the one reported in part 1 (~1.6 nm). Under optimal imaging conditions, the ion-beam
current on a target is found to depend only on the properties of the ion source and to be the same as those of
macroscopic FIB systems regardless of their operating voltage.
PACS numbers: 81.16.Nd