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Focused Ion Beam (FIB)
A Focused Ion Beam (FIB) makes use of Ga-ions to remove
material with a very high spatial precision. In this way cross-
sections can be made on a specifi c location. The resulting
samples can either be studied directly in the FIB or they can
be transferred to a SEM or TEM for more detailed analysis.
When both Ga-ions and certain gases are applied, it is also
possible to deposit material. Therefore, the FIB can be used
as a multifunctional tool in a broad range of applications.
•TEM/SEMsample
preparation
•Failureanalysis
•Cross-sectionanalysis
•Sub-micronmodification
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Fig. 1: Using the FIB, holes with various shapes were
sputtered in a Mo-covered Si3N4 film. The large circle
at the top part of the image was sputtered at the
highest current. For the smaller features visible at the
bottom lower currents were used.
Basic principle
AFocussedIonBeam(FIB)isinmany
wayssimilartoaSEM(ScanningElectron
Microscope).Themaindifferenceisthat
ionsareused,insteadofelectrons.MostFIB
instrumentsareequippedwithaGaLiquid
MetalIonSource(LMIS).Bycombining
heatingwithacertainextractionvoltage,a
Ga-ionbeamisobtained.Asetofmagnetic
lensesfocusestheionsandallowsscanning
oftheionbeamoveradedicatedarea.The
ionbeamcanbeusedforlocalremoval
(“sputtering”),localdeposition,aswellasfor
imaging of material.
Sputtering
ThemostcommonapplicationoftheFIBis
theremovalofmaterialbysputtering.Aset
offileswithmaterial-dependentsputterrates
andpre-programmedshapes(i.e.donuts,
rectangles,polygons)makesitpossibleto
remove material at a desired location with
desired dimensions.
Fig. 3: The route for preparation of cross-section
samples for SEM or FIB as illustrated by SE images
acquired in the FIB. In (A) a patterned poly-Si
structure on a SiO2 covered Si-wafer is visible.
The thin line visible at about the middle of the image
had to be imaged in cross-section in the SEM. In (B)
the Pt-protection layer is deposited on the feature
of interest. In (C) the staircase-like construction is
sputtered. In (D) the sample is tilted 45º and hence
the cross-section can be imaged.
Varyingthecurrentoftheionbeam
influencesthesputterrate.Ahigherbeam
currentincreasesthesputterratebut
decreasestheresolution.Therefore,higher
currentsareusedtoremovelargeamounts
ofmaterial,whereaslowercurrentsareused
forprecisesputteringoffeatureswithsmall
dimensions(seefig.1)andforthefinalstage
inthesputterprocess.
Deposition
By means of a needle a gas can be injected in
the sample chamber. Depending on the gas
components,sputterratescanbeinfluenced
ormaterialcanbedeposited.Forexample,by
crackingavolatilemetal-organicPt-precursor
athinstripconsistingofplatinumcanbe
deposited.Similartosputtering,thedesired
locationanddimensionsofthePt-stripcan
beadjusted.SuchaPt-stripcanbeusedas
an electrical contact or as a protection layer.
TheelectricalcontactscanbeusedforIC-
modification or for realising electrical test
structures,e.g.toelectricallyaddresssemi-
conductingnanowires.
Pt
A B Pt
SiO2
Cu
Cu
poly-Sicontact
A B
C D
Pt-protection
staircase-likeconstruction
Si-substrate
Si
poly-Si Pt
SiO2
SiO2poly-Siline
Fig. 2: (A) a three-layer system viewed in cross-section in the FIB. In the bottom part of the images a thick Cu-
layer is visible: the different shades in grey correspond with different crystallographic orientations. (B) displays a
detailed view of (A). On top of the Cu-layer a black comb-like structure is visible. This is a hole-pattern in the
Cu filled up with SiO2. The top (grey) layer is the Pt-protection layer.‘
Imaging
Whenanionbeaminteractswithmaterial,
secondaryelectronsaregenerated.These
secondaryelectrons(SE)canbedetected
andusedtoformanimage.TheSEyield
depends on the kind of material and
crystallographicorientation.Grainsthatdiffer
in their crystallographic orientation with
respect to the ion beam will have different
brightnessintheSEimage(seefig.2).Hence,
information on grain size and crystallographic
distributioncanbeobtained.
Sample preparation
Manymethodsexisttopreparecross-
sectionalsamplesforSEMorTEMstudies.
Amongstthemarefracturing,cutting,
polishingorthe‘Schlieff ’-method.However,
theabove-mentionedmethodsarenot
sufficientifeither
1)theopticalmicroscopyassisted
preparationfailsbecausethefeatureof
interest is too small or hidden in between
non-transparentlayers,or
2)delaminatingorsmearoutoffeatures/
layersofinterestoccurs.Inthesecases,
FIB-preparationisessential.
Sample preparation for SEM or FIB
Beforesputteringisstarted,aPt-based
protection layer is deposited on the location
ofinterest(seefig.3AandB).UsingtheFIB
itispossibletosputteraholeinthesurface
withonesteepedge(oriented
perpendicularlytothesamplesurface)
at the region of interest and a step like
constructionattheoppositeside(seefig.
3C).Inthiswayitispossibletomakeacross-
sectionthatcanbestudiedbytiltingthe
sample45°.Thecross-sectioncanbestudied
eitherdirectlyintheFIB(seefig.3D)orin
theSEM.Repeatedlysputteringandimaging
thecross-sectioncanreveal3D-information.
AdvantagesofaFIBcross-sectionanalysisare
1)thegoodcontrastincrystallinematerial
and2)thefactthatthesampleisnot
exposedtoairaftermakingacross-section.
However,limitationsaretheresolutionof
~7nm(dependingonthematerialspresent),
thesputteringofthecross-sectionsurface
while imaging and the lack of possibilities
toobtaincompositionalinformation.These
might be reasons to choose for the SEM to
performthecross-sectionanalysis.
20µm 20µm 20µm
20µm 50µm 10µm
A B C
D E F
Fig. 4: Lift-out TEM sample preparation example. (A) displays the surface of a sample in which two parallel trenches are sputtered. In between the trenches a membrane
is situated containing the feature of interest. In (B) the sample is tilted 45º and the bottom of the membrane is cut loose by sputtering. (C) displays the membrane after
attachment (by means of Pt-deposition) to the lift-out needle: the membrane is cut loose from the right side now. After cutting loose the left side of the membrane
the sample can be lifted-out, like shown in (D). In (E) the sample is attached to a supporting grid that fits in a TEM-holder. After cutting loose the lift-out needle, the
membrane gets its final thinning to obtain optimal electron transparency. In (F) the supporting grid is tilted 45º and the cross-section made can be checked in the FIB.
The sample is now ready for TEM study.
©2012 Koninklijke Philips Electronics N.V.All rights reserved.
Characteristics
Sample type:
•Solidmaterial;non-conductive
materials have to be coated with a
20nmconductivelayer(Pt).Additional
protection/contrast layers of Al or
Si3N4aredepositedifrequiredoutside
the FIB.
•Biologicalmaterial(tissue)whenitis
chemically fixated.
Sample size:
•4x4x2cm(lxwxh)maximum
Magnification:
•300x-800,000x(FIB);
•32x-1,280,000x(SEM)
Imagingresolution:
•7nm(FIB),1.1nm(SEM)
Sputtercharacteristics:
•Lateralresolution:<15nm
•Largestdimensions:lateraldimensions
upto100x100µm,depth:30µm
Deposition:
•Pt,WandTEOScanbedeposited
Layerthickness:20µmmaximum
Width:50nmminimum
Length:100µmmaximum
(dependingonwidth)
FinaldimensionsofSEM/TEMsample:
•Minimumfeaturesize:50nm(inonly
one direction: the other direction
needstobebigger)
•Width:maximally60µm
•Depth:30µmforSEM;8µmforTEM
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TechnicalNote19
May 2012
Sample preparation for TEM
ForTransmissionElectronMicroscope(TEM)
analysisaverythinsample(membrane)
isneeded(thickness~100nm).Sucha
thickness is necessary to allow transmission
oftheelectronsthroughthemembrane.At
the desired location on a sample a membrane
containingthefeatureofinterestislifted-out
(seefig.4AtoD).Thismembraneisattached
toasupportgridthatfitsinaTEM
specimen-holder(seefig.4EandF).Both
atomicresolutionimagingaschemicalanalysis
onnanometerscalearepossibleonsuch
membranesinaTEM.
Small Dual Beam (SDB)
TheSDBisamachinethatisequipped
withbothaSEMandaFIBcolumn.This
combination has several advantages.
1)Across-sectionmadeusingtheFIBcan
beimageddirectlyusingtheSEMwithout
exposuretoair.
2)Automationsoftwareenablestheserial
sectioningandimagingthroughasite-
specificvolume.Theacquiredimage
series can be merged into a movie or
reconstructedtoa3D-image.Inthisway,
3-dimensionalmorphologicalinformation
isobtained,forexampleonlocaldefects,
crack propagation or delamination.
3)Inaddition,electronbeamassisted
depositionofPt,WandTEOSispossible.
Applications
•troubleshooting
•layerthicknessdetermination
•cross-sectionanalysis
•thicknessmodification
•nanometerscalefeaturefabrication
Ni/P surface in which a pattern is milled based on a bitmap-file.