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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Materials Analysis

offersafullrangeofanalyticalmethodsand

expertisetosupportbothresearchand

manufacturing,servingcustomersbytaking

anintegral,solution-orientedapproach.

World-class expertise – working for youFor more information:

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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.