Download FIB-based target preparations of complex material systems for

Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
FIB-based target preparations of complex material systems for advanced
TEM investigations
U. Muehle1, S. Jansen2, L.Hillmann3, H.-J. Engelmann2 and D. Rafaja1
1
TU Bergakademie Freiberg, Inst. of Materials Science, Gustav-Zeuner-Str. 5, D-09599 Freiberg
Globalfoundries Dresden, Modul One LLC & Co. KG, Wilschdorfer Landstraße 101, D-01109 Dresden
3
Infineon Technologies Dresden GmbH, Koenigsbruecker Str. 150, D-01099 Dresden
2
Increasing number of TEM-investigations and particularly the request for very special studies leads to a higher demand for
target preparations. The Focused Ion Beam technique (FIB) is able to cover a large amount of these requirements. In this
contribution the principles of FIB-based target preparations are demonstrated on some example from the semiconductor
technology. Using this technique several challenging sample preparations even for special techniques like TEM
holography and/or TEM tomography that requires a very high quality of the samples could be performed. Furthermore
possible consequences of the damage of the specimen by the ion beam and the possibilities, how to avoid this damage, are
discussed.
Keywords TEM; Preparation; Focused Ion Beam, Lift-Out
1.Introduction
In the last years the number of TEM investigations in material science strongly increased. This trend is caused by the
necessity of understanding the materials behaviour on the nanoscale and is supported by the vendors of the TEMs and
FIBs, who introduced more and more TEM-applications to reliable utilization [1, 2]. Furthermore several sectors of
industry are acting in dimensions, which require inspections by TEM. One of the key players in downgrading the valid
dimensions of the products is the semiconductor industry that went below 0.3µm in defined structures still in the early
1990’s [3], which required functional layers of less than 10nm thickness. Consequently, the dimensions of these
structures have to be controlled frequently by TEM, which led first to formation of TEM laboratories near to production
sites [4] and finally to the demand for more, faster and more reliable preparation techniques. Whereas a target
preparation of the single device down to 350nm is possible by a combination of the mechanical preparation and broad
ion milling [5], this approach fails in case of smaller sizes due to missing possibility of the optical control.
Fortunately in the early 1990’s Liquid Metal Ion Sources (LMIS) as the main feature of FIB machines were ready for
production [6]. These machines fulfill the demand of semiconductor industry for an exact control of the devices and
their features. The consequence was the dominance of semiconductors industry in development, technical design and
market share of FIB respectively FIB/SEM combinations mainly in the first decade of their availability on the market.
So a large amount of accessories was dedicated to handle wafers and pieces of them in this machines. The high
standards of industrial customers lead to a fast development of these machines to high quality and reliability, expressed
in uptimes rates larger than 90% and Mean Time between Failure (MTBF) values of several hundred hours.
One of the main utilizations of the FIB-machines from the beginning was the target preparation of TEM-samples [7].
The techniques for realization were improved very fast in terms of reliability and time to result [8], driven by the
expectations of industrial users, where the success of failure analysis directly influences the economical results. The
utilization of these experiences in other fields of application, especially in materials science, where composite materials
and the complex relations between their components and phases play a more and more important role, is the key for
TEM-characterizations at locations, which are hard or impossible to provide.
2.The H-bar technique
A very broadly applied kind of the TEM samples preparation by FIB is the so called H-bar technique, named according
to the appearance of the specimen from the top that is similar to the letter “H”. This technique enables any previously
defined target to be isolated in form of a slice, which will be attached to grid1, transferred in the preparation machine
and thin the requested location with a large amount of freedom in final geometry. [9]
The specified target on the wafer has to be isolated in a slice of about 1.5mm width a 50µm thickness using the
equipment of mechanical preparation like sawing and grinding (fig. 1). The availability of a commercial wafer saw
shortens this step down to about 15 minutes. The slice will be glued to a half moon grid of copper or a thrust ring half.
1
The expression “grid” does not refer to real grid with meshes. It is a more or less commonly used name for the part on which the specimen is
mounted and is responsible to a safe handling in the TEM samples holder as well as in the preparation machine.
1704
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
Some commercial equipment on the market overtakes all steps from the target definition to the optimized sample
geometry for FIB treatment [10]. The first step in the FIB preparation is to cover the target against ion beam damage by
deposition of a protective layer (fig. 2). This layer can be deposited using the Ion Beam Induced Deposition (IBID) or,
if the target of the analysis is situated close to the samples surface, by Electron Beam Induced Deposition (EDID) in a
FIB/SEM-combination and leads to sharp edges on the top during final cutting. The mostly used precursors for the
deposition contain platinum, tungsten or silicon oxides. The second step in the FIB preparation is the removal of larger
amounts of surrounding material using higher ion currents, creating the “H”. Utilization of gas injection systems (GIS)
for gas enhanced etching, e.g. I2 or XeF2, avoids redeposition and shortens the preparation time, but it can only be
applied if the sample contains no components, which are sensitive to the gases like Cu. For thinning of electron
transparent regions lower currents are to be used in two or three steps, where the option “polishing cross section” with a
slice by slice removal of material is recommended. In a FIB-SEM combination [11, 12] the achievement of the target
level can be controlled very exactly. Results of the TEM characterization can be supplemented by SEM images of both
sides of the foil, documenting the exact location of the lamella.
50µm
Cu grid
1.5 mm
Fig. 1 General method for isolation of a target (bright square) for the preparation of a H-bar specimen using a wafer saw and mount
it on a half moon grid.
Fig. 2 H-bar technique for preparation of a TEM-specimen: The target is protected by a platinum bar and large patterns using high
ion currents take care for a path for the TEM (left). Smaller ion current cut a fine lamella (centre). On the right part the whole
geometry of the sample is demonstrated.
TEM specimens prepared this way are usually very robust. Depending on the periodicity of the structures an
additional preparation of locations for comparison is possible as well as keeping parts as reserve for a 2nd attempt (fig.
3, right). For challenging analysis a sequence of a first “rough” preparation, stopping at 100…150nm thick foil, primary
inspection in TEM and careful final thinning until 50nm or less improves the success rates. Restrictions are given by
allowed range of tilting in the TEM due to the channel, which the TEM beam has to pass for imaging.
©FORMATEX 2010
1705
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
Fig. 3 Multilevel preparation of a plane view sample from an integrated circuit. The electron image (left) enables to control the
target levels. In the centre the different levels are demonstrated and the TEM-image (right) shows the functional details.
In order to be able to fulfill special requests like a preparation parallel to the surface (“plane view”) of the wafer a
mechanical polishing until a few µm to the target can be used. The milling direction parallel to the surface of the wafer
enables a very exact definition of the level of the TEM lamella in a complex structure. This can be done for several
levels at adjacent positions leading to a complete characterization of complex structures (fig. 3).
3.Lift-out techniques
The lift-out techniques do not require a special mechanical treatment of the sample to produce a geometry which is
suited for both the FIB and the TEM. The specimen can be extracted from the wafer (or any other material surface part)
using special equipment. So these approaches are preferred to extract a specimen out of the production line and keep the
wafer for further processing and possibly extracting additional specimen some production steps later [13]. A second
reason for development of these techniques was the intention to reduce the preparation time in order to realize the
demand to faster results and higher throughput of samples, required by technologists.
3.1
Ex-situ lift-out
These techniques are characterized by the involvement of a second machine for extraction of the specimen. The TEM
sample is completely prepared, including final thinning to electron transparency, while mounted with small bar at the
surroundings (fig. 4). The extraction of this specimen can be realized under an optical microscope with a large working
distance, enabling to manipulate between objective and sample. A second precondition is the availability of
manipulators with very reliable and sensitive movements. Former approaches used a needle of glass using a
combination of adhesion and electrostatic forces [14], which are strong enough to break the remaining attachment of the
lamella.
Fig. 4 TEM specimen, prepared for the Ex-situ lift-out method: The
specimen is completely thinned and separated from the surrounding
material. Two small connections, which will be destroyed during the
lift-out procedure keep the specimen in the right position.
The specimen extracted this way will be put on a TEM-grid with a carbon film2. Whereas the glass needle put the
sample without any possibility of control to the grid, newer solutions use a hollow needle for picking up and putting
down the specimen [15]. This enables a high precision management during removing the sample out of the wafer as
well a defined positioning at the grid (fig. 5). If necessary this technique is qualified for working on a whole wafer in
the production line. Preparation of the specimen can be done by single beam instrument and extraction of the sample
takes few minutes only. The presence of a carbon foil overlaying the sample reduces the contrast but this is not critical
2
Here a real grid mainly consisting of copper with meshes is used. To keep the specimen it is overlaid with a thin carbon foil. The best parts available
are regularly perforated, which gives the chance to transmit the sample without the influence of continuous carbon layer.
1706
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
for imaging only. For elemental analytics it may be a detractor. It might be an issue, that after preparation no more
corrective actions like additional thinning, plasma cleaning or other can take place.
Fig. 5 Ex-situ lift-out preparation: The TEM specimen is focussed by a visible light microscope (left). A needle approaches and
breaks it out of the sample (centre) and lays it down to TEM grid with a perforated carbon foil (right).
3.2
In-situ lift-out
In contrary to the technique described before, all steps of the in-situ lift out preparation have to be done inside the FIB
machine. The main feature is a micromanipulator, carrying the specimen out of its origin location to a special TEM grid
where it has to be attached. Some early approaches realized this operation in a single beam instrument [16], but the
availability of FIB/SEM combinations gave raise to a broader distribution of this technique.
First the target has to be covered and the surrounding material has to be removed using high ion currents. In contrary
to the procedure described in section 3.1 the specimen keeps a thickness of 1µm or more and remains at the
surroundings by a stable connection, small enough for interruption by the ion beam in a short time. There are different
versions for a proper geometry of the specimen to be extracted (fig. 6). In a following step a micromanipulator
approaches to the specimen and is be attached by IBID with the GIS-system (fig. 7). Now the specimen can be cut
completely free and the micromanipulator picks it up and moves to a safe position.
The second part of the procedure starts with changing the sample against a special TEM grid3, containing “teeth” for
mounting the specimen [17]. The micromanipulator with the specimen has to be approached carefully to the edge
(alternatively the top) of one tooth and the specimen will be mounted using IBID again. After that the connection
between the micromanipulator and the specimen is cut. Final thinning using low ion currents can be done similarly the
H-bar technique (fig. 8). All degrees of freedom including second time thinning, SEM imaging of surface etc. are
available.
Fig. 6 Two options of the primary preparation of an In-situ lift-out preparation: On the left side the sample is completely released
by large FIB-patterning, on the right image cuts from different directions meet each other in a deeper level.
3
See note a: The expression grid is here the commercial used name of the part again.
©FORMATEX 2010
1707
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
Fig. 7 Sequence of in-situ lift-out preparation: The micromanipulator approaches (top left), will be mounted on the separated
specimen (top centre), which is released (top right). Then the specimen will be moved away (low left), will be approached to the
TEM-grid (low centre) and is attached by Pt- or W-deposition (low right).
Fig. 8 TEM-specimen after in-situ lift-out preparation: The region of
interest is final thinned for application of the TEM-technique of choice.
It should be noted, that so prepared lift-out samples are well suited for some special techniques in the TEM. In
comparison to H-bar samples, the absence of surrounding material leads to lower amounts of secondary excitation in
EDX-analysis [18]. For investigations using diffraction and diffraction contrast the free standing sample enables large
tilting angles to adjust different excitation conditions [19]. In comparison to the ex-situ lift-out method, where
frequently losses of samples have to be taken into account, a success rate near 100% for the preparation can be
achieved.
4. Non-semiconductor applications
4.1 H-bar technique for any geometry
For applications in the semiconductors industry the conditions for H-bar technique are favoured. The thickness of a
wafer fits very well to dimension which is allowed by the geometry of the grid and the target is located on the top. Only
the lateral dimensions have to be achieved by mechanical preparation. In case of any geometry these conditions should
be created. This may be realized by preparation of a piece in the allowed dimensions. Figure 9 demonstrates the
preparation of Ti-based sheet material, where the H-bar preparation enables to investigate the deformation mechanisms
1708
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
depending on the distance to the surface, here in the central part of the sheet. A disadvantage of this method is the
possibility to define a target location, restricted to the options which are given by mechanical treatment.
Fig. 9 Titanium based sheet material (1), mounted on a
TEM half moon grid (2). For the final preparation (3) the
location can be selected at any level of depth.
Cross sections at layers systems can be prepared by FIB, when mechanical pretreatment until a proper thickness for
broad ion milling fails. Here grinding and polishing is only necessary until the dimensions of the slice to be mounted on
the half-moon grid. Especially in complex or thicker systems the FIB allows a very exact definition of the mostly
interesting location.
4.2 Lift-out of a metallographic section
In many cases the detachment of the target region as a slice with dimensions suited for FIB out of the system is
challenging or impossible. On the other hand metallography supports a lot of experiences in preparing metallographic
sections for Optical Microscopy (OM) or Scanning Electron Microscopy (SEM) of complex situations like small
bondings, tips of cracks etc. The desire of TEM investigations at several details after a characterization by visible light
microscopy, SEM or even X-ray diffraction (XRD) could be satisfied using the lift-out technique at the metallographic
section observed by the mentioned methods before. The preconditions for such an experiment are good due to the
excellent surface of a metallographic section.
Fig. 10 Metallographic section with a solder connection, prepared for in-situ lift-out preparation of a TEM sample at specified
location (left). The height of the sample is reduced to 3…5 mm, defined by the samples holder of the FIB tool. In a SEMcharacterization (right) the components solder material (1), intermetallic phase (2) and basic material (Ni - 3) is identified.
The first step for the realization is to reduce the samples dimensions to a value covered by the recipient, usually in
term of height and take care to a good conductivity to ground (figure 10). Sometimes it is recommended to mark the
region of interest by microhardness indentations because contrast behaviour in FIB may differ, complicating the
relocation. The following steps are equal to the described in-situ lift-out procedure and consist of (a) removing the
©FORMATEX 2010
1709
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
surrounding material, (b) approaching and mounting the micromanipulator, (c) cutting and removing the specimen, (d)
approaching and mounting it to the grid and (e) final thinning to electron transparency. It should be noted, that the
sputtering behaviour of complex material systems may differ strongly from well known samples (e.g. silicon). This has
to be taken into account in definition of pattern dimensions and depths. Figure 11 [20] demonstrates the results of
complex investigations of solder joint. Here the primary metallographic preparation including SEM characterization
was the best choice to meet the target region before starting the TEM preparation.
Fig. 11 Result of complex TEM characterization after lift-out preparation: The specified grain of the intermetallic compound (1 in
left picture) was investigated by electron diffraction in three zone axis. In combination with an EDX-analysis the phase could be
recognized as Cu6Sn5, where Cu is partly substituted by Ni [20].
4.3 Applications at complex materials systems
Based on the experiences of chapter 4.2 a broad variety of materials and systems can be prepared by lift-out technique.
In many cases it is not required to prepare a perfect metallographic section. The existence of a well polished surface,
meeting the target region, is the only precondition. Examples for application are the cross sections of layers, where the
substrate was too brittle for the isolation of a TEM sample by sawing and/or grinding (fig. 12) or grain boundaries of a
solar cell with conspicuous behaviour in electrical tests (fig. 13). In general it should be noted that the lift-out
techniques enlarges the possibilities of TEM-target preparations to all cases, where a reliable preparation of an exact
metallographic preparation succeeds. The availability of in-situ lift-out techniques extends the TEM preparations to
almost every location like tips of cracks etc.
Fig. 12 TEM preparation of a brittle substrate (SiN) with a Si-layer for investigation of phase boundary behaviour and orientation
relations: Two parts of the sample were glued “face to face” and polished using metallographic techniques (left) for the extraction of
a TEM specimen (centre), thinning and TEM-observation (right).
1710
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
Fig. 13 Grain boundary in solar silicon, to be recognized by the
etching behaviour: The deposited Pt bar defines the location of the insitu lift-out for characterization of the grain boundary. It should be
noted, that the lift-out preparation can be applied without a
mechanical treatment of the sample.
5. Requirements of special TEM techniques
The development of special techniques in the broad field of TEM requests special ways for specimen preparation taking
into account the special circumstances of these techniques. Due to the control by FIB and/or SEM imaging the
requirements of well defined thickness (e.g. for spectroscopic and diffraction methods) can be fulfilled, much better
than by other methods. Additional requirements are formulated by techniques like off-axis holography or 3D
investigations using tomography of multiple views.
5.1 Electron holography
The electron holography is a powerful tool for a more detailed microstructure analysis, as it allows not only the
intensities but also the phase shift to be observed [21, 22]. One application is the imaging of variations in the mean
inner potential of doped regions in semiconductor devices [23], leading to a better understanding of the technological
steps. The FIB technique is indispensable for the sample preparation and opens a wide field for holographic
applications, although some additional challenges are to be taken into account [24]. It is necessary to allow a vacuum
beam travel within the field of view, which is restricted to less than one µm to the detecting system. Furthermore the
method is very sensitive to variations in sample thickness, so that in practice no curtaining effects (see below) are
allowed.
The key to avoid the curtaining effect, which is mainly caused by cutting through very different material, is to make
sure that the ion beam meets only homogeneous material. This can be performed by removing all material with different
sputtering behaviour before starting the FIB steps [18] or by changing the geometry in a way that the ion beam comes
not from the top direction [25]. The excellent possibilities for controlling the ion beam in a FIB/SEM-combination
brought the required region in the TEM lamella and achieved the desired samples thickness. The results are specimen
with MOS transistors in a short distance to the edge of the sample (fig. 14), enabling a path of the vacuum beam to
bring it to interference.
Fig. 14 Two examples for FIB-based target preparation of electronic structures for electron holography: At the left hand side the
transistor structure was situated at the edge of a H-bar sample and the vacuum beam could be situated beside. In the centre a lift-out
technique was used and the final polishing was realised by a direction, which was former horizontal. The right picture shows the
visualisation of the doped areas (white arrows).
©FORMATEX 2010
1711
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
5.2 Electron tomography
For 3D-investigations using electron tomography high tilting angles are necessary [26]. Whereas the electrochemically
thinned or broad ion milled samples can fulfil these conditions in most cases, FIB processing is restricted in removed
volumes due to the long preparation times for removal of larger amounts of material. Using the lift-out techniques the
material surrounding the target has a smaller volume and a complete dispensation can be done. The positioning of the
extracted slice on top of the tooth and the selection of a parallel direction to the rotation axis allows the full range of tilt
angles of the tomography holder (fig. 15).
As shown recently [27] it is recommended to prepare a specimen with pillar shape for tomography. This leads to a
constant thickness at the whole range of acquisition angles.
Fig. 15 TEM-specimen for electron tomography: The left picture demonstrates the principle of the free standing sample and the
rotation over a wide angular range (+/- 70°). The preparation of 3 identical pillars is to seen in the centre, looking down parallel the
ion beam. TEM-overview of the pillar system is demonstrated at the right.
5.3 TEM in multiple viewing directions
There are issues, in which the exact definition of the location of the target cannot be realized before starting the
preparation, like in complex electronic devices, where several transistors are working together in a manner that doesn’t
allow to specify, which transistor is responsible for a dysfunction. Then a rough TEM observation of the whole system
using larger foil thickness and a low magnification can lead to more detailed assumptions about the origin of the failure.
A complete understanding of the failure mechanism can be achieved by a more detailed investigation from another
point of view. Using a careful Electron Beam Induced Deposition (EBID) for protection of the specified location
enables further preparation steps in order to detach a specimen perpendicular to the first plane by second lift-out [28].
The present example shows a partial plane view of an integrated circuit covering the levels from silicon substrate to the
lowest contacts (fig. 16), identifying the probable location of the fail. A lift out of this region from the plane view
sample allows the detailed description of the origin of the fail.
Fig. 16 TEM preparation for two directions of observation a one location: At the left the preparation for plane view of a larger area
before application of lift-out is shown. In the centre the area of special interest (squares) was found by TEM plane view imaging. The
dashed lines describe the location of the cross section, prepared out of the plane view specimen and shown on the right.
1712
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
6. Samples damage
6.1 Amorphisation and Ga-penetration
The bombardment of a specimen with 30kV accelerated Ga ions doesn’t occur without strong influences on the
structure. Ga ions penetrate deep in the hard core and destroy the bindings in the same manner as any sputtering process
like in case of a Secondary Ion Mass Spectrometry (SIMS) measurement [29]. The depth for direct and lateral
penetration can be calculated using Monte Carlo Simulations [30].
Fig. 17 Cross section of a TEM lamella, demonstrating the
amorphous region due to influence of highly accelerated Ga ions:
Amorphisation above the silicon occurred during deposition of the Ptbar and at the sidewall during final polish using 30kV and a small
current density.
For a TEM sample this leads to amorphisation of the upper regions and the side wall of the TEM lamella (fig. 17,
[31] [32]). The range of amorphisation depends on the material and achieves more than 20nm in silicon in lateral
direction. Other materials like tungsten or crystals with a high amount of packing density like TiN are less sensitive.
Whereas the destruction on the top of the sample can be easily avoided by deposition of a protective layer or EBID, the
amorphous layers at the sidewalls reduce the amount of useful information in the specimen and downgrade the signal to
noise ratio. Especially for sensitive investigations like High Resolution Imaging and EELS, where often very thin foils
are necessary, this layers should be removed. Actual tools offer the reduction of acceleration voltages for the ion
column down to 1 or 2 kV, applied to the final polishing steps. The reduction of the acceleration voltage to 5kV and 2
kV leads to noticeable thinner amorphous layers, demonstrated at a Si single crystal (fig. 18 [33]).
Fig. 18 Effect of reduced acceleration voltage on the lateral amorphisation of a Si-specimen during FIB-polishing
Using the Time-of-Flight Secondary Ion Mass Spectroscopy (ToFSIMS [34]) an investigation of the penetration
depth detected Ga deeper than the amorphous layer [35]. The so measured Ga depth profile depends on the acceleration
voltage too (fig. 19 [35]). Using the FIB preparation the appearance of Ga in an elemental analysis (e.g. by EDX)
should be always taken into account as a preparation artefact. For investigations, where effects of band structure
influence the result the presence of impurity traps due to low concentrations of Ga cannot be neglected [36].
©FORMATEX 2010
1713
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
Fig. 19 Lateral depth of Ga
penetration during final FIB polishing
for different acceleration voltages: It
should be noted that the Ga
penetration exceeds the thickness of
the amorphous region significantly.
6.2 Curtaining
An additional effect in FIB preparation is the so called “curtaining” effect [37]. Materials with different sputtering
behaviour above the region of interest influence the angle at the edge of the FIB cut, resulting in different foil
thicknesses below (fig. 20 [19]). Unfortunately this effect increases with lower acceleration voltages (fig. 21) like used
for high quality samples.
Fig. 20 FIB-prepared TEM-sample: The wedge-like
interference patterns (a, marked by the white line) allow
an estimation of the regions of equal foil thickness.
Below the presence of more heavy material like WSi2
(b) they come closer to the upper edge of the substrate
and below cavities (c), offering no resistance to the ion
beam, they appear in a larger distance to the edge of the
substrate.
In order to avoid this effect, all different material, especially structured details, above the region of interest [38] has
to be removed. Alternatively the direction of the ion beam with respect to the objects to be prepared may be changed,
which requires some special ideas about the samples geometry and the planned kind of TEM-investigation [25].
Fig. 21 Influence of reduced acceleration voltage on curtaining effect: Whereas the full voltage of 30kV polishes leads to minor
curtaining effect, which would be only visible in the TEM (left), a 2kV-polish leads to strong curtaining still at locations with small
differences in the material above (right, see white arrows).
1714
©FORMATEX 2010
Microscopy: Science, Technology, Applications and Education
A. Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
7. Summary
The utilization of the FIB preparation, particularly in a combination with SEM, enables to solve a lot of very different
requests for TEM investigations at very restricted locations and at challenging combinations of materials. Standard
techniques like the H-Bar technique were developed for the semiconductors industry, where FIB machines are fast and
wide distributed in many laboratories and manufacturing sites. This technique can be applied to a lot of issues in
material science.
The availability of lift-out equipment, especially of micromanipulators for in-situ lift-out enlarges the variability of
preparation techniques and simplifies the mechanical preparation to that of the usual preparation of a metallographic
section.
Acknowledgements Parts of this work were supported by by the Ministry of Education and Research of the Federal Republic of
Germany (Project No. 13N9432). Furthermore the authors thank the company FEI for the cooperation during common tool
development projects and tool demos. Special thanks to the staff of the TEM laboratories of Qimonda/Infineon Dresden and
Globalfoundries Dresden for providing us with of unpublished results and to the technical staff of the Institute of Materials Science at
the TU Bergakademie Freiberg for support.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
Williams, D.B., Carter, C.B.; Transmission Electron Microscopy; New York: Springer Science+Business Media, 2009
Reimer, L., Kohl, H.; Transmission Electron Microscopy; Springer; New York: Science+Business Media, 2008
http://www.itrs.net/Links/2009Winter/Presentations/Conference/ORTC_121609.pdf
Stegmann, H., Engelmann, H.-J., Zschech, E.; Transmission Electron Microscopy in Semiconductor Manufacturing;
Microscopy Book Series, Vol. I; 2006; http://www.formatex.org/microscopy1/content.htm
Cerva, H., Huber, V., Eckers, W., Mitwalsky, A.; Specific preparation procedures for failure analysis of (sub)micron areas in
silicon devices; ultramicroscopy 52 (1993): 127-140
Forbes, R.G.; Understanding how the liquid-metal ion source works; Vacuum 48 (1997): 85-97
Giannuzzi, L.A., Stevie, F.A.; Introduction to Focused Ion Beams; New-York: Springer Science+Business Media Inc., 2005
Engelmann, H.-J., Volkmann, B., Blum, W., Zschech, E.; TEM-Zielpräparation in einer Stunde – Utopie oder realistisches Ziel;
Praktische Metallographie 39 (2002): 139-149
Basile D, et al. "FIBXTEM - Focussed Ion Beam Milling for TEM Sample preparation."Specimen Preparation for Transmission
Electron Microscopy of Materials 111, (ed.) R. Anderson, Materials Research Symposium Series 254, pp 23-41 (1992).
http://www.camtek.co.il/php/index.php?option=com_content&task=view&id=314&Itemid=250
http://www.fei.com/products/dualbeams/
http://www.smt.zeiss.com/C1256E4600305472/Contents-Frame/9C02420A02765BC1C1256E5800335569
Muehle, U., Jansen, S., Schuetten, R., Prang, R., Schampers, R., Lehmann, R. ; High volume TEM-sample preparation using a
wafer saving in-line preparation tool; 14th emc Aachen 2008
Giannuzzi LA, Drown JL, Brown SR, Irwin RB, Stevie FA. Focused ion beam milling and micromanipulation lift-out for site
specific cross-section TEM specimen preparation. In: Anderson RM, Walck SD, editors. Materials Research Society
Symposium Proceedings, vol. 480. Pittsburgh, PA: Materials Research Society, 1997.
http://www.fei.com/uploadedFiles/Documents/Content/2008_05_TemLink_ds.pdf
Kamino, T., Yaguchi, T., Kuroda, Y.,Hashimoto, T., Ohnishi, T., Ishitani, T., Umemura, K., Asayama, K.; A newly developed
FIB system for TEM specimen preparation; microsc.& microanal. 8 (2002); 48-49
http://estore.omniprobe.com/m1webgear/ProductSearch.aspx?Group=GRIDS
Huebner, R., Engelmann, H.-J., Zschech, E.; Effect of TEM sample preparation on quantitative EDXS analysis of SiGestructures; submitted to Appl.Phys. Lett.
L. de Abreu Vieira, M. Döbeli, A. Dommann, E. Kalchbrenner, A. Neels, J. Ramm, H. Rudigier, J. Thomas, B. Widrig:
„Approaches to influence the microstructure and the properties of Al–Cr–O layers synthesized by cathodic arc evaporation”,
Surface & Coatings Technology 204 (2010), 1722-1728
Muehle, U., Jansen, S., Leinert, S., Breuer, D.; Preparing a TEM sample from a polished metallographic section; Pract. Met. 43
(2006); 306-315
Lichte, H., Lehmann, M.; Electron holography - basics and applications; Reports on Progress in Physics 71 (2008): 1-46
Midgley, P.A.; An introduction to off-axis holography; micron 32 (2001): 167-184
Rau, W.D., Schwander, P., Baumann, F.H., Höppner, W., Ourmazd, A.; Two-Dimensional Mapping of the Electrostatic
Potential in Transistors by Electron Holography; Physical Review Letters 82 (1999): 2614-2617
Lenk, A., Lichte, H., Muehle, U.; 2D-mapping of dopant distribution in deep sub micron CMOS devices by electron holography
using adapted FIB-preparation; Journal of Electron Microscopy 54 (2005): 351-359
Muehle, U., Sickmann, J., Hillmann, L.; Focused Ion Beam (FIB)-basierte Zielpräparation an Transistoren der 70 nmGeneration zur Elektronenholographie; Praktische Metallographie 46 (2009): 509-520
Midgley, P.A., Weyland, M.; 3D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM
tomography; ultramicroscopy 96 (2003): 413-431
Ritz, Y., Stegmann, H., Engelmann, H.-J., Zschech, E.; Zielpräparation von Proben für 3D-TEM mittels Mikromanipulator;
Praktische Metallographie 44 (2004): 180-189
Hillmann, L., Prang, R., Muehle, U., Oesterreicher, I.; TEM-Präparation in drei Raumrichtungen zur Defektanalyse; Praktische
Metallographie 46 (2009): 292-302
©FORMATEX 2010
1715
Microscopy: Science, Technology, Applications and Education
A.
Méndez-Vilas and J. Díaz (Eds.)
______________________________________________
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
1716
Oppolzer, H., Rehme, H., Fuchs, E, Particle Beam Microanalysis. Fundamentals, Methods and Applications; Wiley-VCH; 1991
Ziegler, J.; http://www.srim.org/
Engelmann, H.-J.; Vor- und Nachteile der TEM-Probenpräparation mittels FIB; Praktische Metallografie 40 (2003) 163-174
Rubanov, S., Munroe, P.R.; FIB-induced damage in silicon; Journal of Microscopy 214 (2004) 213-221
Mühle, U., Steinhoff, J., Hillmann, L.; Influence of FIB-acceleration Voltage on Lateral Damage of Silicon based TEMsamples; Microscopy Conference 2007; Saarbruecken
http://www.ion-tof.com/technique-sims-IONTOF-TOF-SIMS-TIME-OF-FLIGHT-SURFACE-ANALYSIS.htm
Mühle, U.; Steinhoff, J.; Estimation of Lateral Ga-Penetration in FIB using ToF-SIMS and EDS in TEM; Workshop "Focused
Ion Beams in Research, Science and Technology" Dresden; 22.5.2006
Lenk, A.; Quantitative Messung von Dotiergebieten in FIB-präparierten Silizium-Halbleiterbauelementen mittels
Elektronenholographie; PhD-Thesis; TU Dresden; 2008
Schwarz, S., Kempshall, B., Gianuzzi, L., McCartney, M.; Avoiding the Curtaining Effect: Backside Milling by FIB INLO;
Microscopy & Microanalysis 9 (2003); 116-117
Mühle, U., Lenk, A., Lehmann, M., Lichte, H.; Visualisation of Electrically Active Areas Using Electron Holography; ISTFA
2002
©FORMATEX 2010