Challenges and Opportunities for Focused Ion Beam
Processing at the Nano-Scale
J. Gierak
1
*, B. Schiedt
1
, D. Lucot
1
, A. Madouri
1
, E. Bourhis
1
, G. Patriarche
1
, C. Ulysse
1
,
X. Lafosse
1
, L. Auvray
2
, L. Bruchhaus
3
, and R. Jede
3
1
LPN/CNRS, Route de Nozay, F-91460 Marcoussis, France,
2
MPI, Université d’Évry Val d’Essonne, Bd. François
Mitterrand, 91025 Évry Cedex, France,
3
RAITH GmbH, Hauert 18, Technologiepark, D-44227 Dortmund, Germany
*
jacques.gierak@
lpn.cnrs.fr
Introduction High-Resolution Nano-Writing Instrument Using Ions
There is a solid consensus that new methods of structure A few years ago we decided to develop a FIB system
fabrication, placement, and organization within the sub-10-nm having global specifications compatible with nano-fabrication
resolution gap are urgently required to meet existing challenges experiments [1], that is, a deep sub-10 nm nano-device
in condensed matter, semiconductors, and biotechnologies. fabrication capability. In particular we were aiming at focusing
Standard top-down methods such as resist-based lithographies on a target—a FIB spot capable of fabricating directly and
even used at the shortest available wavelengths have clearly reproducibly nano-devices on materials as diverse as III-V
identified limitations. On the other hand, bottom-up semiconductors, metallic layers, thin- or ultra-thin films, or
approaches, like scanning probe manipulation techniques, even atomically thin suspended graphene sheets [2].
remain challenging when trying to generate reproducible, The ion emitter. The Liquid Metal Ion Source (LMIS) is
functional, and addressable nano-structures. Therefore, at the a simple, compact, and quasi-perfect point-type ion source.
laboratory level new routes must be explored. Therefore, we have examined several kinds of LMIS and
The patterning of samples using Focused Ion Beams (FIB) is decided to optimise a gallium ion emitter. This optimisation
a very popular technique in the field of inspection of integrated allowed us to obtain a record on-axis angular intensity of up
circuits and electronic devices. This is the case mainly for to 80 µA/str and an extreme stability of the emission process
prototyping devices. The FIB technique allows 3D patterning (current variations less than 0.5 percent per hour). At this
of target materials using a finely focused pencil of ions having stage, long unattended nano-fabrication processes without the
speeds of several hundreds of km/second at impact. Although need of thermal heating cycles to recover adequate emission
most metals can be used in FIB technology as pure elements characteristics can be envisioned, opening the route to practical
or in the form of alloys, gallium (the Ga
+
ion) is preferred in and reproducible nano-patterning applications.
most cases. Practically, FIB patterning can be achieved either by The ion optics. Our FIB column concept was built on a
local surface defect generation, by ion implantation, or by local patented concept where the source region is physically separated
sputtering. These adjustments are obtained easily by varying the from the focusing and transport optics via a beam-defining
locally deposited ion fluence with reference to the sensitivity of aperture. The lens designs, shapes, and operation modes have
the target and to the selected FIB processing method. been evaluated and selected against FWHM probe diameters
A B
Figure 1: (A) Schematic view of the high-resolution FIB nano-writer. A compact single beam ion column is placed perpendicularly to a laser interferometer controlled
stage (2 nm accuracy). (B) Picture of the instrument in our laboratory facilities.
14 doi: 10.1017/S1551929509000479
www.microscopy-today.com • 2009 September
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