ADVANCES
IN FOCUSED ION BEAM MICROSCOPY :
FIB 2001
Friday 30th March
2001
Department of Materials, Oxford University, U.K.
ABSTRACTS
The FIB preparation
of TEM samples: Methods and applications for semiconductor device
materials
S. Newcomb, University of Limerick, Limerick, Ireland
Focused ion beam
(FIB) microscopes have made a significant impact over the last few
years, particularly in the field of semiconductor device technology.
Usage of FIBs within the industrial senario is paralleled by the activities
of a number of academic laboratories and now extends well beyond routine
device modification and imaging applications. FIBs have found widespread
use in the preparation of TEM samples, for example, and this too has
in turn led to a diversification of the applications of TEM. Some
of the ways in which samples for both cross-sectional and plan-view
TEM examination can be prepared using a FIB will be described. The
range of problems that can be usefully addressed will be illustrated
with examples taken from recent TEM studies of semiconductor devices.
Whilst the FIB will be shown to have a number of advantages over traditional
methods for TEM sample preparation, some of the problems that can
occur will also be described and techniques by which artefacts can
be minimised discussed.
Focused ion beam
analysis of Cu/low-k metallisation structures
H. Bender, IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
The introduction
of Cu metallisation with low-k dielectric materials in the next generations
of electronic devices requires the investigation of the properties
of these materials during the different application modes of the Focussed
Ion Beam (FIB) analysis.
Cu has a high secondary electron yield during the Ga ion imaging and
the ion beam quickly removes the native oxide. Therefore excellent
channeling contrast can be obtained and applied to studies of the
spontaneous or annealing induced Cu grain growth, via and trench filling,
and voltage contrast analysis of shorts in devices. Some examples
related to process developments will be discussed.
Three different classes of low-k materials can be distinguished, i.e.
organic polymers, porous oxides and carbon doped oxides (Si-O-C).
Several low-k materials immediately show a FIB-contrast reversal indicative
of the formation of a conductive surface layer by the implanted Ga.
This behaviour, which is of concern for device editing applications,
will be discussed for some low-k dielectrics.
For device modifications, the behaviour of the Cu and low-k materials
during gas assisted etching, i.e. their selectivities, enhancements,
and etch rates are important. Data on some relevant materials will
be discussed. Cu shows an in-situ corrosion when exposed to halogen
gasses (I2, Cl2, Br2) and furthermore a long memory effect is present
due to I2 absorbed in the system.
For specimen preparation for transmission electron microscopy (TEM),
the FIB milling technique is a major choice for devices with low-k
materials as these are soft and therefore easily get deformed by the
conventional preparation procedures for TEM specimens, which involve
polishing techniques. Data on the smoothness of FIB specimens containing
Cu/low-k structures will be discussed.
FIB for MEMS and nanotechnology
P. Prewett, Microsystems Manufacturing and Nanotechnology Group, The
University of Birmingham, Edgbaston Birmingham B15 2TT, United Kingdom
The last decade
has seen a significant growth in microelectromechanics (MEMS), leaning
heavily upon the microfabrication tools and processes used in the
silicon semiconductor industry. Using a combination of optical lithography
with well established deposition and etch methods, centres such as
Sandia Laboratories have developed complex electromechanically actuated
mechanical systems based on polycrystalline silicon. Alternative fabrication
routes include the use of bonded single crystal silicon on insulator
(BSOI) wafer stacks and electroplated metal MEMS, manufactured using
X-Ray lithography, by the LIGA process. Integrated chip MEMS packages
are commercially available, such as the miniature accelerometers from
Analog Devices Inc. Applications range from accelerometers for vehicle
airbags to inertial guidance and control systems.
Just as focused ion beams have found use for repair and modification
of silicon ICs, they will be increasingly important in the MEMS field.
Their use for customised modification of MEMS devices and fast turnaround
prototyping will grow rapidly, particularly for the smallest devices
as MEMS research enters the realm of Nanomechanics.
Nanotechnology requires removal and deposition to produce features
of 100nm or less, which is within the range of FIB technology. With
advanced computer driven pattern generation systems developed for
electron beam lithography, FIB machines provide uniquely versatile
tools for Nanotechnology. The new NanoFIB programme at Birmingham
University is designed to exploit these capabilities for a range of
Nanotechnology projects over the next decade.
Focused ion beam nanolithography for metal masks
D-J Kang, G. Burnell, M. Blamire and W. Huck2, Department of Materials
Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ
2 Melville Laboratory, Department of Chemistry, University of Cambridge,
Pembroke Street, Cambridge CB2 3RA
Focussed ion
beam workstations are well known for their use as tools for direct
micromachining and TEM specimen preparation but they can also be used
to realise a large area nanoscale patterning method in a relatively
easy way. We have developed an ion beam lithographic technique with
which we can achieve ultrahigh resolution patterning in a metal mask.
We are applying this mask patterning technology to the fabrication
of a master that can be used for nanocontact (im)printing. This strategy
would allow large scale manufacturing of nanostructures.
Implanted Ga+ passivates Nb in a CF4 plasma, therefore Ga irradiation
can be used as a hard mask while unirradiated regions will be etched
in a conventional CF4 reactive ion etching system. We have obtained
a metal mask with deep sub-micron scale features by combining the
focussed ion beam lithography in metal mask and reactive ion etching.
We will discuss the details of this technique and its great potential
as a simple method for producing nanostructures.
3D analysis of deformed nanostructures using FIB
B. J. Inkson, T. Steer, H. Wu, O. Kraft2 and G. Möbus, Department
of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, beverley.inkson@materials.ox.ac.uk,
2MPI für Metallforschung, Stuttgart, Germany
Focused ion beams
can be used as a 'nanoknife', cutting materials into slices to examine
their internal structure. By cutting many parallel 2D cross-sectional
slices of known orientation, and aligning them in the computer, it
is possible to build up 3D maps of features such as grain boundaries,
phase boundaries and cracks. This technique provides completely new
information on 3D microstructures in the 100nm-30mm size range between
existing 3D TEM, X-ray and optical methods.
This paper details progress made in the quantification of the deformation
of nanomaterials, using the site-specific 3D mapping technique to
relate 3D microstructure to local mechanical property measurements.
The 3D FIB technique has been applied to (a) 3D mapping of deformation
under nanoindentation sites, (b) 3D analysis of crack modes in alumina-based
nanocomposites, and (c) evolution of 3D grain shape in intermetallic
nanocomposites. Errors inherent in the 3D FIB and 3D FIB-SEM techniques
are discussed.
FIB as a tool
for enhancement of depth sensing indentation test methods
P. Trtik and P. J. M. Bartos, ACM Centre, University of Paisley, High
St, Paisley , PA1 2LH, Scotland, UK. pavel.trtik@paisley.ac.uk
This paper provides
a summarised review of applications of focused ion beam (FIB) techniques
applied for enhancement of depth sensing indentation (DSI) test methods.
Nanotechnology-based DSI test methods are increasingly important tools
for characterisation of mechanical properties of materials. By utilising
the nanoscale resolution of the ion column, the FIB techniques show
a large potential for the improvement of depth sensing indentation
test methods. The applications can be categorised into the following
areas:
(i) Nanomachining of diamond probes - diamonds, the hardest naturally
occurring material, shaped into a three-sided pyramid are usually
used as indenter tips for DSI test methods. FIB milling techniques
show potential for production of the tip whose depth- area-function
is closer to the ideal shape than that produced by conventional methods.
Production of other specially shaped diamond probes, such as those
that are suitable for push-out tests of sub-10mm-diameter filaments
in fibre-reinforced composites, is also presented. The influence of
the FIB milling process on the mechanical properties of the FIB-machined
diamond probes is discussed.
(ii) Post-indentation observation (cross-sectioning of the indents)
- FIB techniques can be used for microstructural examination of micro/nanoindents.
An indent could hitherto be observed only from "above" as
an impression into the surface of the tested material. In its cross-sectioning
mode, the FIB workstation enables the material to be etched out in
such a manner that the previously unavailable but very important observation
of the microstructure of the material underneath the indent can be
carried out. Such cross-sections reveal entirely new information about
the 'third dimension' of the microindents and about the microstructure
of the sub-surface material surrounding the indent.
(iii) Pre-indentation preparation of the specimens - three-dimensional
objects of various sizes, such as beams, cantilevers, can be FIB-machined
in the structure of the specimen. Such a nano/microbeam or a nano/microcantilever
is then loaded in indentation apparatus. Since the dimensions of the
micromachined object can be measured with a high precision and the
deflection vs. load diagram is monitored during the DSI experiment,
the elastic modulus of the material of microbeam/microcantilever can
be derived from the classical beam bending theory.
A method for TEM specimen preparation from specific sites and its
application to materials science
T. Kamino, Hitachi Science Systems, Japan
A method for TEM specimen preparation from specific sites using a
combination of FIB and TEM microscopies has been developed. First,
a specimen is roughly FIB milled to the thickness of 3-5 mm, and then
transferred to a STEM microscope for localization of the site of interest
by STEM and SEM imaging at an accelerating voltage of 200kV. STEM
imaging tells us the fine structure of the site, and SEM imaging tell
us the depth of the site from both sides of cross sections.
After STEM and SEM characterisation, the specimen is brought back
to the FIB system for further milling to prepare the electron transparent
thin foil specimen. A FIB-TEM compatible specimen holder is employed
in the method, and both FIB milling and STEM/SEM imaging are possible
without remounting the specimen on the holder
The advantage of the method in comparison with the standard FIB technique
is that less damage is incurred due to no use of Ga+ ion beam for
localization of the site. Positional accuracy of the method in localization
of the site is 100nm or better. Applications of the method with respect
to failure analyses, evaluation and characterizations of various electronic
devices will be also discussed.
In addition, a micro-sampling technique to lift out small samples
directly from bulk samples inside a FIB system will be also discussed,
together with the details of the operations and the applications.
Fabrication of nanoscale superconductor-normal metal-superconductor
junctions by FIB
G. Burnell, R. H. Hadfield, C. Bell, D. J. Bell, D. J. Kang, S. J.
Lloyd and M. G. Blamire, Department of Materials Science, University
of Cambridge
We have developed
a reliable and versatile technique for fabricating SNS Josephson junctions
with a focussed ion beam microscope in conjunction with an in-situ
resistance measurement technique. This provides a simple method that
allows us to create a variety of single and multi-junction superconducting
devices (arrays, SQUIDs and 3 terminal devices) with desirable and
well controlled properties and high integration densities.
Here we discuss the development of this technique, demonstrating the
versatility of the FIB in this application with recent results from
arrays intended for use in voltage standards, SNS SQUIDs being developed
as particle detectors and superconductor-ferromagnet-superconductor
junctions.
IC passive component modification using Focused Ion Beam
B. Domenges*, B. Feron, J-P Gaslondes, H. Murray*, P. Descamps* and
A. Doukkali*,
Philips Semiconductors, *LAMIP, 2 rue de la Girafe BP 5120, F-14079
Caen Cedex 5, France
Beside multiple
applications of focus ion beam technology, device modification appears
to be of a high interest. Indeed, the combination of powerful imaging,
selective milling and metal deposition capabilities allows prototype
IC device modifications at component and metal circuit line scale.
Here, we present the use of FIB to validate the improvement of IC
performances through passive component modification.
The idea was to decrease the volume of resistive deposited components
in order to simulate higher resistance. Thus using the FIB, an IC
has been milled down to the component level, and an adequate volume
milled out. Subsequent electrical characterisations showed modified
performances but not as good as expected. Then, FIB cross section
of modified IC allowed to observe the conical shape of the drilled
area. Due to the depth of the component to be modified (5 microns),
it appeared thus necessary to take into account this conicity effect.
Further successful experiments allowed us to conclude that it is possible
to increase of a desired value the resistance of a passive deposited
component by milling part of its volume. FIB technology definitely
appears to be an adequate tool to IC device modification at component
scale.
Failure analysis of magnetic resistance head by an optical beam head
induced current method and Focused Ion beam
K. Sakaguchi, T. Sakata, S. Takasu and S. Aoyagi, JEOL Ltd., 1-2 Musashino
3-chome, Akishima, Tokyo 196-8558, Japan
Recent magnetic
recording devices, taking in and introducing new core technologies
for magnetic resistance (MR) head, feature an extremely high surface
recording density. Therefore, yield management has become a critical
issue in MR head production. Traditionally, magnetic devices were
inspected optically, and defective chips were selected by electrical
probing. However, these techniques are effective for inspection at
chip level, but are unable to identify defects confined in the chips
for further analysis. As the MR head pattern density is increasing,
the defects must be identified and analyzed to enhance yield. Presently,
review-systems are requested which are capable of accurate analysis
of such defects that conventional optical or electrical testing fails
to detect. Responding to this requirement, we experimented with a
laser microscope, and a focused ion beam (FIB) system. The defect
part of the MR head can be detected nondestructively by the OBHIC
method with a laser microscope. In addition, the OBHIC image is verified
with FIB by analyzing the detected defect part, and the cause of the
defect can concretely be specified at the same time. The automated
defect analysis, by which the laser microscope is coordinate-linked
with the FIB, is being promoted based on these results.
Direct observation of deformation under nanoindents by transmission
electron microscopy in focused ion milled specimens
S. J. Lloyd, J. M. Molina-Aldareguia and W. J. Clegg, Department of
Materials Science and Metallurgy, University of Cambridge, Pembroke
Street, Cambridge, CB2 3QZ, UK
Nanoindentation
is now widely used to measure the mechanical properties of nanostructured
materials. However to understand the hardness values obtained it is
necessary to examine the deformation processes occurring under the
indent. Transmission electron microscopy (TEM) is ideally suited to
examine the defect structures caused by indentation at the atomic
scale required but in the past its application has been limited by
the difficulty in making a cross-section through a specific site on
the specimen such as a nanoindent. This has recently been made much
more straightforward through the use of the focused ion beam (FIB)
microscope that allows electron transparent windows of uniform thickness
to be machined at local regions of interest in the specimen.
We shall describe the method used to prepare cross-sections through
nanoindents in the FIB. A variety of materials are being examined
including semiconductors, metals and ceramics as well as nitride multilayers.
TEM images of the region under the indent will be used to determine
the dominant deformation mechanism in each case with the aim of understanding
the relationship between the hardness and the flow stress in different
materials.
POSTERS:
TEM sample preparation
of compound semiconductor devices using an in-situ micromanipulator
and ion mill
T. Matsuda, Y. Murayama and K. Yabusaki, Yokohama R&D Laboratories,
The Furukawa Electric Co., Ltd., 2-4-3, Okano, Nishi-ku, Yokohama
220-0073, Japan
Compound semiconductors
which are represented by InP and GaAs, are widely used for optical
and electronic devices. For transmission electron microscopy (TEM),
these devices need to be prepared by focused ion beam (FIB) because
of their size. During the FIB preparation, the milled surfaces of
these devices suffer from two kinds of damage. One is the formation
of an amorphous layer that contains implanted Ga atoms. Another is
the precipitation of In and Ga particles on the surface. These damage
effects result in serious problems in high resolutional electron microscopy
(HREM) and the analytical electron microscopy (AEM) because of observational
obstruction and compositional fluctuations. Therefore, we have applied
ion milling after the FIB thinning to remove the damaged layers.
Although the sample shape for ion milling should be flat to keep low
incident angle, thinned samples by FIB have a general concave shape.
To make the whole sample have the same thickness, we picked up small
fragments that include the parts to be observed from the devices,
and joined the fragments to thin Al foils using a micromanipulator
inside the FIB chamber. The fragments were thinned to be designed
thickness with the Al foil using FIB. Lastly, ion milling was applied
to the samples only for a short time. As a result, TEM samples of
the specific desired region of the compound semiconductor devices
with little damage were obtained.
Preparation by FIB of TEM metal alloy specimens containing corrosion
cracks
S. Lozano-Perez, M. L. Jenkins, R. Langford and J. M. Titchmarsh Department
of Materials, University of Oxford
FIB systems can
be used for the preparation of TEM cross-section specimens of a wide
range of materials. A major potential advantage of using a FIB system
over established preparation techniques such as broad beam ion milling
is that a specimen can be prepared to within 50nm of a specific point.
This capability makes FIB an ideal tool for the preparation of TEM
specimens through cracks in metal alloys such as steels. However,
such use of FIB is not well documented. The study by TEM of the faces
and tips of the cracks should give insight into crack growth mechanisms,
especially when the cracks are the result of corrosion processes.
Here, we report on the preparation of specimens of cracks in steels
using a FIB system. Artifacts of FIB preparation such as ion implantation
and ion milling of the original surface/oxide and procedures used
to preserve the microstructural features of the cracks are discussed.
A comparison of a 3D FIB map and an AFM scan of the surface of a nanoindentation
deformation zone
T. J. Steer, G. M. Steer, G Möbus, O. Kraft2, T. Wagner2 and
B. J. Inkson, Department of Materials, University of Oxford, 2Max-Planck-Institut
für Metallforschung, Stuttgart, Germany
A novel technique
has been developed to examine site-specific, subsurface microstructures
in three dimensions (3D). A 3D data set is collected by successive
cross-sectional slicing using a gallium focused ion beam (FIB) and
imaging using ion-induced secondary electrons, enabling a 3D microstructure
map to be generated using computer-based reconstruction techniques.
This 3D FIB mapping technique has been applied to a copper-titanium
epitaxial metal bilayer coating which has been deformed by nanoindentation.
The 3D FIB map of the surface of the indent has been compared to the
equivalent map produced by an atomic force microscope (AFM). Although
the FIB technique is usually most advantageous when examining subsurface
structure, mapping the surface allows the errors to be discussed with
reference to the AFM scan. Ways in which the errors might be reduced
are suggested.
Since this 3D FIB mapping approach is not limited to multilayer coatings
or deformation caused by nanoindentation, and could be applied to
any material with subsurface structure of interest; it provides a
unique and exciting insight into site-specific, subsurface microstructure.
Preparation of CuInS2 Thin Film Solar Cell Cross Sections for HREM
C. Kaufmann, S. Gledhill2, R. Langford2, J. L. Hutchinson2, J. Klaer3,
R. Klenk2 and P. J. Dobson, Engineering Department, University of
Oxford, Parks Road, GB-Oxford OX1 3PJ, 2Materials Department, University
of Oxford, Parks Road, GB-Oxford OX1 3PH, 3Hahn-Meitner-Institut Berlin
GmbH, Glienicker Strasse 100, D-14109 Berlin
TEM cross sections
of CuInS2 thin film solar cells have been prepared using a FIB system.
The solar cells are multi-layered structures with a layer sequence
of Mo/CuInS2/BufferLayer/ZnO supported by a glass substrate. In the
past the highest efficiencies for CuInS2 thin film solar cells have
been reached using a CdS buffer layer. However, recently there is
growing interest in developing a Cd-free chalcopyrite solar cell with
alternative buffer materials, such as In(OH)xSy. Therefore an extensive
characterisation of the buffer layer structure is necessary. Here,
we report on our work to examine the structure of our Cd free buffer
layers deposited by chemical bath deposition using TEM. The TEM cross
sections have been prepared using a FIB system and the effect of broad
ion beam milling, chemical assisted milling and low energy milling
on the high-resolution TEM analysis have been investigated.
Nano Machining using Focused Ion Beam
F. Morrissey, FEI Electron Optics, Building AAE, Achtseweg Noord 5,
P.O. Box 218, 5600 MD Eindhoven, The Netherlands. fmorriss@nl.feico.com
Focused ion beam
systems have been used for site specific milling of micro structures
for some time. Recently there has been interest in machining on the
nano scale for MEMs applications. Modern FIBs can achieve milled features
~10nm on silicon.
During the milling process, these structures have conventionally been
imaged using the focused ion beam. For true nano-scale materials,
such ion beam imaging can give insufficient resolution and also sample
degradation. The combination of Field Emission SEM, coincident with
the ion column overcomes such restrictions. Examples of nano machining
and applications will be given with some particular examples coming
from the material science market.
FIB analysis of biological specimens
P. J. Heard, A. C. Oyedepo and G. C. Allen, Interface Analysis Centre,
University of Bristol, BS2 8BS
Biological specimens
are frequently difficult to analyse because of their complexity, their
electrically insulating nature and their incompatibility with ultra-high
vacuum. If their analysis requires high spatial resolution and high
sensitivity, the problems encountered are compounded. Quantitative
analysis of such specimens can be carried out only under carefully
controlled conditions and with appropriately chosen instrumentation
and calibration specimens.
Examples of the analysis of such specimens are discussed. SIMS has
been used in the detection of low levels of boron in animal tissue
in order to study a potential cancer treatment, boron neutron capture
therapy (BNCT). Also, the analysis of tissue surrounding artificial
hip joints, and the analysis of plant tissue are described.
One choice of technique in these cases is SIMS with a gallium focused
ion beam and a magnetic sector mass spectrometer. Such an instrument
gives the required sensitivity and spatial resolution, and dynamic
SIMS conditions are used here in a high-vacuum environment (10-8 mbar).
The acquisition of quantitative information requires the preparation
of standard samples.
Possible choices of technique are discussed, as well as issues associated
with sample preparation, analysis regimes and interpretation of results.
Application of a Focused Ion Beam system to sample preparation and
micro and nanoengineering
R. Langford and A. K. Petford-Long, Department of Materials, University
of Oxford, Parks Road, Oxford, OX1 3PH, UK
The capability
of focused ion beam systems to sputter, ion implant and deposit metals
and insulators in user defined areas make them ideal tools for micro-
and nanoengineering and sample preparation for microanalysis. Here
we discuss our current uses of a focused ion beam system for sample
preparation and micro- and nanoengineering and examples, such as the
preparation of transmission electron microscopy cross-sections for
high resolution electron microscopy and atom probe specimens and the
milling of 2D and 3D shapes are outlined.
Focused Ion Beam milling in the preparation of transmission electron
microscope specimens of non-semiconducting materials
P. Munroe, Electron Microscope Unit, University of New South Wales,
Sydney, NSW 2052, Australia
The focused ion
beam (FIB) miller is an instrument that is widely used, and accepted,
in the preparation and analysis of semiconductor materials and integrated
circuits. However, more recently, its presence has begun to expand
into more general materials science applications. Here, the FIB is
rapidly find applications in, for example, the study of thin film
structures, nanoindentation studies and the examination of wear surfaces.
One application of the FIB is the preparation of transmission electron
microscope (TEM) specimens from materials that have proven difficult
to prepare using more traditional techniques.
This paper will illustrate the scope of the FIB in the preparation
of TEM samples from a wide range of non-semiconducting materials including
internally carburized stainless steels, metallic and ceramic powders,
advanced ceramics, Raney catalysts, composite materials and coated
or implanted steels. The presentation will examine the development
of FIB-based preparation techniques to suit particular specimen types,
the significance of the microstructures observed, the type and extent
of any artifacts generated and the development of methods to minimise
or control artifacts.
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