FIB Machining

Focused Ion BeamMicroscopy andMicromachining

C.A.Volkert and A.M. Minor, Guest Editors

ion–solid interactions that lead to the var-ious functionalities of FIBs. In the topicalarticles that follow, the major subspecial-ties of FIB research are discussed.

The FIB InstrumentThe basic functions of the FIB, namely,

imaging and sputtering with an ion beam,require a highly focused beam. A consis-tent tenet of any focused beam is that thesmaller the effective source size, the morecurrent that can be focused to a point.Unlike the broad ion beams generatedfrom plasma sources, high-resolutionion beams are defined by the use of a fieldionization source with a small effectivesource size on the order of 5 nm, thereforeenabling the beam to be tightly focused.

The ion source type used in all com-mercial systems and in the majority ofresearch systems designed with microma-chining applications in mind is the liquid-metal ion source (LMIS).6,7 Of the existingion source types, the LMIS provides thebrightest and most highly focused beam(when connected to the appropriateoptics). There are a number of differenttypes of LMIS sources, the most widelyused being a Ga-based blunt needlesource. Ga has decided advantages overother LMIS metals such as In, Bi, Sn, andAu because of its combination of lowmelting temperature (30∞C), low volatility,and low vapor pressure. The low meltingtemperature makes the source easy todesign and operate, and because Ga doesnot react with the material defining theneedle (typically W) and evaporation isnegligible, Ga-based LMISs are typicallymore stable than other LMIS metals.During operation, Ga flows from a reser-voir to the needle tip (with an end radiusof about 10 mm), where it is extracted byfield emission. A large negative potentialbetween the needle and an extractionelectrode generates an electric field ofmagnitude 1010 V/m at the needle tip. Thebalance between the electrostatic forcesand the Ga surface tension wetting thetapered W needle geometry results inthe formation of a single Taylor cone at theneedle tip. For typical emission currentsused in FIB microscopes (~2 mA), a cuspforms at the tip of the Taylor cone with atip radius of approximately 5 nm.

The simplest and most widely used ionbeam columns consist of two lenses (acondenser and objective lens) to definethe beam and then focus it on the sample,beam-defining apertures to select thebeam diameter and current, deflectionplates to raster the beam over the samplesurface, stigmation poles to ensure aspherical beam profile, and a high-speedbeam blanker to quickly deflect the beam

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AbstractThe fairly recent availability of commercial focused ion beam (FIB) microscopes has

led to rapid development of their applications for materials science. FIB instrumentshave both imaging and micromachining capabilities at the nanometer–micrometer scale;thus, a broad range of fundamental studies and technological applications have beenenhanced or made possible with FIB technology. This introductory article covers thebasic FIB instrument and the fundamentals of ion–solid interactions that lead to themany unique FIB capabilities as well as some of the unwanted artifacts associated withFIB instruments. The four topical articles following this introduction give overviews ofspecific applications of the FIB in materials science, focusing on its particular strengthsas a tool for characterization and transmission electron microscopy sample preparation,as well as its potential for ion beam fabrication and prototyping.

IntroductionThe focused ion beam (FIB) microscope

has gained widespread use in fundamen-tal materials studies and technologicalapplications over the last several yearsbecause it offers both high-resolutionimaging and flexible micromachining in asingle platform.

The FIB instrument is similar to a scan-ning electron microscope (SEM), exceptthat the beam that is rastered over thesample is an ion beam rather than an elec-tron beam. Secondary electrons are gener-ated by the interaction of the ion beamwith the sample surface and can be usedto obtain high-spatial-resolution images.In most commercially available systems,Ga ions are used, and their sputteringaction enables precise machining of sam-ples. In conjunction with the gas-injectioncapabilities on these systems, whichenable ion-beam-activated deposition andenhanced etching, a range of sample fabri-cation schemes are possible.

During the last 25 years, FIB instrumen-tation has become an important technol-ogy for a wide array of materials scienceapplications, from circuit editing andtransmission electron microscopy (TEM)sample preparation to microstructuralanalysis and prototype nanomachining.Most modern FIB instruments supple-

ment the FIB column with an additionalSEM column so that the instrumentbecomes a versatile “dual-beam” platform(FIB–SEM, see Figure 1) for imaging,material removal, and deposition atlength scales of a few nanometers to hun-dreds of microns. The FIB instrumentbecomes a powerful tool for nanomanipu-lation and fabrication through the aug-mentation of an FIB instrument withmicromanipulators and gas injection forlocal chemical vapor deposition (CVD).

The first FIB instruments evolved fromadvances in field ion microscopes1 andthrough the development of high-resolution liquid metal ion sources(LMISs).2–4 In the 1980s, FIB instrumentswere embraced by the semiconductorindustry as offline equipment for mask orcircuit repair. It was not until the 1990sthat FIB instruments began to be used inresearch laboratories, and today there arecommercial instruments available frommultiple manufacturers.5 With the popu-larity of FIB instruments for TEM samplepreparation, microstructural analysis, andnanomachining, dual-beam FIB instru-ments are becoming a versatile and pow-erful tool for materials researchers.

This introductory article focuses onthe FIB instrument itself and the basic

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off the sample and onto a beam stop suchas a Faraday cup. Because the focusingstrength of an electromagnetic lens isdirectly related to the charge/mass ratioof a particle, it is impractical to build elec-tromagnetic lenses for ions (which wouldweigh thousands of kilograms); thus,focusing and steering are performed usingelectrostatic components rather than theelectromagnetic components used forelectrons.

The size and shape of the beam intensityprofile on the sample determines the basicimaging resolution and micromachiningprecision. Generally, the smaller the beamdiameter, the better the achievable resolu-tion and milling precision, although therequirements for the two applications arenot exactly the same.8 For the energies,currents, and acceptance angles used intypical FIB systems, the beam spot size islimited mostly by the chromatic aberrationthat results primarily from the energyspread of the beam due to space chargeeffects at the ion source and secondarilyfrom the spherical aberration of the lenses.However, the ultimate spatial resolutionfor FIB imaging is, in fact, limited by sput-tering and is thus sample-dependent.9 Inmodern FIB systems, the imaging resolu-tion determined by the sputter-limited sig-nal/noise usually is about 10 nm.

The sample is mounted on a groundedstage with three-axis translation, rotation,and tilt capabilities. The stage is designed

to have a eucentric point (i.e., a well-centered point such that the field of viewis maintained when tilting the specimen)at the location where the two beams cross(or at the working distance of the ionbeam, in the case of a single-beam FIB).The region of interest on the sample ismoved to the eucentric point using trans-lation and rotation and then tilted for thedesired angle of beam incidence. The totalcurrent on the sample (sum of the incom-ing ion or electron beam and all emittedcharged particles) is measured at thestage.

Depending on the application, the vari-ous emitted particles or radiation can bedetected with appropriate detectors in thesample chamber. Traditional detectorssuch as those in an SEM can be used todetect the electrons or x-rays created bythe interaction of the ion beam with thesample. The ions sputtered from the sam-ple can also be detected using a variety ofdetectors such as charge electron multipli-ers, and mass selection of the sputteredcharged particles is also possible (second-ary ion mass spectrometry). FIBs derivean important additional functionalitythrough the use of gas-injection sources todeliver gas locally to either enhance theetching rate or result in site-specific CVD.Secondary electrons generated by the inci-dent ion beam (or, alternatively, theincident electron beam in dual-beam sys-tems) can crack hydrocarbon precursor

gases, leading to local deposition of theconducting material (W, Pt, or C) or insu-lating material (SiO2); see the article byMoberlyChan et al. in this issue. The localdeposition of material also enables sophis-ticated micromanipulation within the FIBchamber, made possible through micro-manipulation accessories and the abilityof the FIB to cut (sputter), paste (deposit),and watch (image) during a manipulationprocess within the chamber. The result is asystem that can image, analyze, sputter,and deposit material all with very highspatial resolution and controlled throughone software program. In a large part, it isthis multifunctional versatility that hasmade FIB instruments popular amongmaterials researchers.

Ion–Solid InteractionsIon–solid interactions play an important

role in many different endeavors, rangingfrom fabrication of microelectronic devicesto understanding distributions of cosmicgases. This brief introduction will belimited to the processes and conditionsrelevant to the use of FIB systems in mate-rials science. For more detailed descrip-tions of ion–solid interactions, the readeris referred to books and review articleson the subject 6,10–12 as well as to literaturespecifically on FIB.13–15

When an ion impinges on a solid, itloses kinetic energy through interactionswith the sample atoms. This transferof energy from the ion to the solid resultsin a number of different processes (seeFigure 2):� ion reflection and backscattering� electron emission� electromagnetic radiation� atomic sputtering and ion emission� sample damage� sample heating

The ion typically comes to rest in thesolid, leading to implantation of the ion.With the possible exception of electromag-netic radiation generation, all of theseprocesses are important to FIB andFIB–SEM system applications and aredescribed in the next sections.

Collision CascadeIon kinetic energy and momentum are

transferred to the solid through bothinelastic and elastic interactions. In inelas-tic interactions (called electronic energyloss), ion energy is lost to the electrons inthe sample and results in ionization andthe emission of electrons and electromag-netic radiation from the sample. In elasticinteractions (called nuclear energy loss),ion energy is transferred as translationalenergy to screened target atoms and canresult in damage (displacement of sample

Focused Ion Beam Microscopy and Micromachining

390 MRS BULLETIN • VOLUME 32 • MAY 2007 • www/mrs.org/bulletin

Figure 1. Schematic illustration of a dual-beam FIB–SEM instrument. Expanded viewshows the electron and ion beam sample interaction.


atoms from their initial sites) and sputter-ing from the sample surface.

The most widely accepted concept forion–solid interactions is the collision cas-cade model16,17 (Figure 2). For the case of5–30 keV Ga impinging on most solids,the collision cascade involves a series ofindependent binary collisions (the linearcollision cascade regime). If the transla-tional energy transferred to a target atomduring a collision exceeds a critical valuecalled the displacement energy, the atomwill be knocked out of its original site, for

example, creating an interstitial–vacancypair in a crystalline sample. This primaryrecoil atom may have sufficient energy todisplace further sample atoms (secondaryrecoils), thus generating a volume wherelarge numbers of atoms have excesskinetic energy. If a displacement collisionoccurs near the surface, the recoil atommay be emitted from the solid and lead tosputtering. The displacement energy (typ-ically on the order of 20 eV) is much largerthan the binding energy for the atoms (ofthe order of 1 eV), reflecting the fact that

the collisions are nonadiabatic, because ofthe very short time scale.

After approximately 10–11 s, the 5–30keV Ga ion comes to rest in the solid, andthe energies of all particles participating inthe cascade have decreased below the dis-placement energy. At this point, the colli-sion cascade has ended. What remains arethe emitted particles and radiation, andion beam damage such as lattice defects,incorporated Ga, and heat, all of whichmay continue to interact and evolve.

Molecular dynamics calculations areideally suited for simulating collisioncascades, because of the short length andtime scales. Monte Carlo calculations arealso well suited to simulating ion–solidinteractions by including the “frictional”electronic stopping and stochastic elasticcollisions. The most widely used MonteCarlo simulation is the program TRIMor SRIM (transport, or stopping range, ofions in matter).18 Such calculations for 30keV Ga into elements from Li to Bi showthat roughly two times as much of the ionenergy is lost to nuclear energy losses thanto ionization energy losses (the formerfrom interactions with the nucleus of anatom and the latter from interactions withthe electrons). Of the nuclear energylosses, the majority is lost through sampleatom vibrations or heating rather thanthrough vacancy formation.

The projected and lateral ranges of the30 keV Ga scale inversely with the sampledensity and are between 10 nm and 100nm (projected) and between 5 nm and 50nm (lateral). TRIM sputtering yields(sputtered target atoms per incomingion) are between 1 and 20 for normal-incidence 30 keV Ga and increase some-what with atomic number.6 However,sputtering yield predictions depend criti-cally on surface binding energies, whichare not well known and are sensitiveto surface structure and chemistry. TRIMvacancy generation predictions between300 and 1000 vacancies per incomingion are overestimates because defectdiffusion and interactions are ignored. Inaddition, discrepancies between experi-mental and simulated ranges and colli-sion cascade shapes in crystals can beexpected, because TRIM samples areisotropic and cannot capture channelingeffects. Despite these limitations, such cal-culations are invaluable in predictingtrends and in estimating the effects ofion–solid interactions.

Ion Beam ImagingIn the same manner that images are

generated in an SEM, the ion beam can berastered over a sample surface and theemitted electrons, particles (atoms and



Figure 2. Schematic illustration of a collision cascade generated by a 30 keV Ga+ ionincident on a crystal lattice, showing the damage created in the collision cascade volume,and the projected range Rp and lateral range Rl of the implanted ion.


ions), and electromagnetic radiation canbe detected. Conventional SEM imaging isbased on detecting the secondary elec-trons (SEs). To date, most imaging in a FIBis based on detecting the low-energy elec-trons, often referred to as ion-induced sec-ondary electrons (ISEs). Typically, 1–10electrons with energies below 10 eV aregenerated per incoming 5–30 keV Ga ion.These electrons are created by both kineticand potential emission from the top fewatomic layers where the primary ionimpacts the solid as well as wherebackscattered or sputtered particles exitthe sample. The total low-energy electronyield depends strongly on surface oxida-tion and contamination and thus willchange as the surface is sputter-cleanedand Ga is incorporated.

Ion beams are not as finely focused aselectron beams and, partly for this reason,they generally offer lower resolution.However, the contrast mechanisms for ISEgeneration are different from those forSE generation and can offer complemen-tary information about a sample surface.SE and ISE images of the same sample areshown in Figure 3. Both the SE (Figure 3a)and the ISE (Figure 3b) images show con-trast due to surface topography and mate-rial differences. However, ISE imagingtypically delivers stronger channeling con-trast from crystals than SE imaging. Thecontrast due to crystal orientation is easilydistinguished from material contrast,because crystal contrast changes with theincidence angle of the ion beam and mate-rial contrast does not. In ideal samplessuch as Cu or Au, ISE channeling contrastcan reveal twin lamellae as narrow as 20nm and grains as small as 50 nm.

The different contrast mechanisms areillustrated in Figure 4. A comparison ofFigures 4a and 4b shows that when thecrystal is oriented so that the ion “chan-nels” along crystal planes, there are fewerion interactions with sample atoms near thesurface and thus fewer electrons are emit-ted. Figure 4c illustrates that heavier sam-ples typically result in more ISEs (and SEs).Figure 4d shows that surface topographycan lead to increases in the number of ISEs(and SEs), because of the increase in thenumber of ion–solid interactions near thesample surface. The SE and ISE images arealso often distinguished by the amount ofcharging generated in insulating samples.

Presumably because of differences inthe low-energy/secondary electron yieldsand to the fact that the Ga implantationcreates a thin conducting layer at the sam-ple surface, the FIB can often be used toimage uncoated samples that are difficultto image even with low-voltage SEM.However, it is important to remember that

ion beam imaging always results in someGa implantation and sputtering of thesample surface.

Ion Beam SputteringBecause of the sputtering action of the

ion beam, the FIB can be used to locallyremove or mill away material. For exam-ple, a Sn sphere is progressively sputteredover a defined area in Figure 5. For directmilling, the limiting feature size is typi-cally about 10 nm9,19,20 (see the articles byMoberlyChan et al. and Langford et al. inthis issue). Quantitative aspects of sputter-ing are complicated and depend on thematerial, crystal orientation, ion beamincidence angle, and the extent of redepo-sition.

As the incidence angle of the ion beamis increased, the intersection of the colli-sion cascade with the sample surfaceincreases, and the number of sputteredatoms per collision cascade increases(a similar effect of geometry on electronemission is shown in Figure 4d).However, at the same time, the fractionof reflected or backscattered Ga ionsincreases. The combination of these twoeffects leads to a maximum in sputteringyield at an incidence angle of approxi-mately 75–80∞. This effect has been con-firmed for 25–30 keV Ga into a variety ofmaterials, including single-crystal Si,19–22

amorphous SiO2,21,22 and polycrystallineAu and W21 and shows good agreementbetween experiment and theory. Si oramorphous solids are ideal for such astudy because the effects of crystal chan-neling are avoided (the surface region ofSi amorphizes under the Ga beam7). Thebehavior is more complicated in crys-talline material where both incident angleand channeling effects are present.21

The sputtering yield at a given inci-dence angle can vary by as much as a fac-tor of 10 for strongly channeling crystalorientations in materials such as Cu.23 Thisis because for easy channeling orienta-



Figure 3. (a) Secondary electron (SE)and (b) ion-induced secondary electron(ISE) images of an FIB-cut crosssection in brass. Surface topographygenerated during the FIB milling andphase contrast are visible in bothimages. The heavier second-phaseprecipitates are bright in the SE imageand dark in the ISE image.37 Channelingcontrast showing the grain structure isvisible only in the ISE image.

Figure 4. Schematics showing the influence of (a), (b) crystal orientation, (c) atomic mass,and (d) surface geometry on 30 keV Ga+ collision cascades and ISE image contrastformation. The orange atoms in (c) are more massive than the yellow atoms in (a), (b), and(d). Similar concepts influence sputtering yields.


tions, the ion experiences only inelasticglancing-angle collisions with the atomslying in a crystal plane and travels deeperinto the crystal before causing elastic colli-sions, so that fewer atoms are sputteredfrom the surface. This is analogous to theeffect of crystal orientation on low-energyelectron yields illustrated in Figures 4aand 4b. Channeling effects on sputteringat a vertical grain boundary in Cu areshown in Figure 6. The grain with thesmaller electron yield appears dark inFigure 6. Its lower sputter yield results ina shallower sputter profile than thatobserved for the brighter neighboringgrain.

The sputter profiles also depend on theexact sequence in which the ion beam is

rastered over the surface.22 For instance,the sputter profile of a ring cut by rapidand repetitive scanning (“multi-pass”scanning) differs from that obtained byslowly scanning the beam just once overthe same area (“single-pass” scanning)(Figure 6). Despite an identical totalion dose (ions per unit area) for both ringsin Figure 6, the slow single-pass scan,spiraling from outside to inside, results ina deeper cut, because of effects of ionfocusing, incident angle effects, and rede-position.

Redeposition decreases the effectivesputter yield and changes sputter profiles.The decreased yield comes about becauseredeposited material lands in the areabeing sputtered and must be sputtered asecond time. Redeposition is also given asa reason why completely vertical side-walls cannot be cut with the FIB withoutover-tilting the sample,13,24 but it is cer-tainly also partly because of the intensitytails of the ion beam profile and of thedecrease in sputter yield at high incidenceangles.19,20,25 Many details of redepositioneffects remain open, such as the develop-ment of crystal orientation and channelingeffects seen in the redeposited material(e.g., Figure 6, single-pass ring).

In addition to redeposition, surfaceroughening and shadowing effects areprevalent during sputtering. An exampleof a shadowing effect on topology duringcross-sectioning with the FIB, the so-called

“curtain effect,”13 is seen in the lower halfof the images in Figure 3. Surface rough-ening, specifically ripple formation, iswidespread during ion bombardment9,26

and is attributed to competition betweensmoothing by surface diffusion or viscousflow and roughening because of surface-curvature-dependent sputter yields. (Thesputter yield depends on local curvaturefor the same reasons it depends on angleof incidence.)

Even during normal-incidence sputter-ing, surface roughening can occur and isdependent on the crystal orientation, asshown in the multi-pass ring cut acrosstwo differently oriented grains in Figure6. Such crystal-orientation-dependentrippling is attributed to anisotropic sur-face diffusion.27 Other unusual effectsof sputtering and redeposition on surfaceevolution continue to be discovered.28,29

Nonetheless, progress is being madetoward models that can predict surfaceevolution during sputtering and can beused to achieve desired sputter profiles(see the article by Langford et al. in thisissue).

Ga IncorporationImaging and milling with Ga ions

always result in Ga incorporation near thesample surface. As the sample surface issputtered away at a rate proportional tothe sputtering yield and the ion flux (ionsper area per time), the Ga is implanted



Figure 5. (a)–(c) Secondary electronimages during sputtering of a large Snsphere surrounded by Sn droplets,using a 30 keV Ga beam rasteredacross a 10 mm ¥ 10 mm area.

Figure 6. Ion-induced secondary electron image of rings milled with 30 keV Ga at a grainboundary in Cu. The single-pass ring shows an enhanced sputtering yield (deeper trough)and redeposition (sloped, thicker sidewalls); the multi-pass ring shows channeling effectsand surface roughening.


further into the sample, and a steady-stateprofile of Ga is reached. The maximum Gaconcentration occurs at steady state afterthe removal of target material to a depthroughly equal to the ion range and is con-stant over a depth also roughly equal tothe ion range. Ignoring the effects frompossible diffusion of Ga in the target mate-rial, differences in molar volume, andpreferential sputtering, the Ga atom frac-tion at steady state is

fGa = 1/(aY), (1)

where a is the fraction of ions that arenot reflected or backscattered from thesample surface, Y is the sputtering yield(number of sputtered atoms/ions perincoming ion)10 and aY is the sputteringyield per implanted ion. Based on thisequation and typical TRIM sputteringyields (from 1 to 20 sputtered atomsper incoming ion), atom fractions from1 at.% to 50 at.% Ga are expected near thesample surface. Because of the increase insputter yield with incident angle, thesteady-state Ga concentration is expectedto be roughly 5–10 times smaller duringglancing-angle sputtering than normal-incidence sputtering. In contrast, channel-ing is expected to raise the steady-state Gaconcentration.

Most studies report Ga concentrationsin good agreement with simulations andtheory, although a few claim to see almostno Ga. Unless the Ga diffuses away oris reflected, it must end up in the surfaceregion of the sample. Some studies wereperformed with energy-dispersive spec-troscopy in an SEM, which for typical elec-tron beam parameters will look throughthe thin Ga-doped layer at the surface andunderestimate the actual Ga concentration.Other studies have used surface Augeranalysis (without sputtering) that mayalso underestimate the Ga concentration,because of the presence of carbonaceous oroxide surface layers. Carbon-based surfacelayers are particularly prevalent in sam-ples that have been imaged in the SEMafter FIB milling.30 In contrast, Augerdepth profiles or chemical analysis inthe TEM give reasonable agreementwith predictions for both Ga concentra-tion and range (allowing for channelingeffects).

All of these considerations becomemuch more complicated in alloys or if Gadiffusion or reactions take place. Oneunusual example is the formation of Ga-containing surface phases during imagingof certain fcc metals (see the article byMayer et al. in this issue). This phenome-non, which is coupled with sample crystalstructure and channeling effects, limits the

ability to obtain high-quality images fromcertain materials.

Ion Beam DamageA major drawback of FIB imaging and

machining, particularly for TEM samples,is the damage created by the ion beam(again, see Mayer et al. in this issue).As the ion dose increases, the individualdisordered cascade regions overlap anda damaged surface layer is formed.Depending in particular on the samplematerial and temperature, the ion beamdamage can take the form of sample sur-face amorphization, point defect creation,dislocation formation, phase formation,grain modification, or other unusualeffects. With the exception of Si amor-phization, systematic investigations of FIBdamage are just beginning. Nonetheless,several trends can be identified based onliterature results for broad beam ions andon anecdotal FIB observations.

Ion beam amorphization is a well-known phenomenon and has been exten-sively studied for covalently boundmaterials such as Si, Ge, GaAs, and C(diamond). Because of the highly direc-tional nature of the atomic bonds incovalent materials and in certain alloys,the atomic rearrangements necessary toheal the disorder created by the ion beamare often hindered. In contrast, pure met-als have nondirectional bonding and donot amorphize. Thus, thin amorphouslayers sometimes observed at the edgeof pure metal TEM samples made byFIB presumably contain impurities suchas Ga, C, or O. Some oxygen gets inbecause of the relatively poor quality ofthe vacuum.

Point defects and dislocation loopscan also be created during FIB imagingand machining. Systematic studies of FIB-induced defects have not been under-taken, although there are many isolatedobservations, both published and unpub-lished. For example, Cu is prone to exten-sive FIB damage,31 as shown in the TEMimage in Figure 7, but Al is not andeven provides reasonable-quality high-resolution TEM samples.32 Tooth enamel(hydroxyapatite) is resistant to FIB-induced damage,33 but other apatitecrystals that decompose at lower temper-atures amorphize easily. Several addi-tional and unusual types of damagehave been observed in FIB-milled sam-ples. These include the formation of Ga-containing surface phases (see Mayeret al., this issue) as well as ion-beam-induced grain growth in fine-grained Niand Ni alloys.34 Preferential sputtering,which is prevalent during FIB milling ofmaterials that decompose at low tempera-

tures, can lead to chemical changes in thesurface region and influence the ease ofdamage formation and amorphization.

Ion Beam HeatingDuring ion implantation, almost all of

the ion kinetic energy is eventuallyconverted to heat, with only a small frac-tion stored as defects in the sample oremitted as energetic particles or radia-tion.14 For times longer than approxi-mately a nanosecond and distances largerthan around 100 nm, the ion beam canbe approximated as a continuous heatsource. At shorter times, there are largetemporal variations in heating, and attimes of less than 10–12 s, the atoms barelyhave time to interact with each other, andthe temperature of the solid is not welldefined.15 The maximum temperaturereached in a sample depends on the beampower P, sample thermal conductivity k,sample geometry, and contact to a heatreservoir.15,35 Beam powers in commercialsystems have maximum values of 1 mW.



Figure 7. (a) Transmission electronmicroscopy (TEM) image of a Cu film,showing that the existing dislocationstructure was modified by FIB milling.(b) Schematic illustration of the millinggeometry. (TEM image courtesy of G.P.Zhang.)


When the ion beam is incident on a flatsurface, the transfer of heat away from theincidence point is so effective that even inthe absence of a heat reservoir (e.g., for asemi-infinite sample), a finite steady-statetemperature increase is reached given by36

T = P/(pak), (2)

where a is the radius of the circular ionbeam profile on the sample surface. Forvalues of P/a available in commercialFIBs, between 1 W/m and 1000 W/m, thetemperature rise predicted by Equation 2can range from entirely negligible for sam-ples with good thermal conductivity tohuge for poor conductors. For example,for Si (k = 148 W/m K) the temperatureincrease is <2∞C even for the most extremebeam conditions. In contrast, for poly-meric or biological materials (k ~ 0.1 W/mK), such small temperature rises are onlyachieved with P/a values of <2 W/m,which is at the low end of what is avail-able in commercial FIBs.

Beam heating can be diminished byplacing samples in good contact with aheat reservoir. On the other hand, whenimaging or machining TEM lamellae,membranes, or other structured samples,much higher temperatures may bereached when the sample geometry limitsthe transfer of heat.35 An extreme exampleof this is when the heat transfer is reducedto one dimension, such as for a cylindricalpillar with a diameter equal to the beamdiameter. In this case, the temperature riseis given by Equation 2 multiplied by theheight-to-diameter ratio of the pillar.Thus, by determining the length-to-widthratio of the thermal path in a structuredsample, a worst-case estimate of the actualtemperature rise can be obtained and usedto select appropriate beam conditions.However, imaging or cutting of high-aspect-ratio features in low-conductivitymaterials may lead to unacceptably hightemperatures, even for the most mildbeam conditions in commercial systems.

In This IssueFour articles follow this introduction

and are intended to cover the most widelyused FIB applications as well as the cur-rent state of the art in FIB materialsresearch. In the first article, by Mayeret al., one of the most important applica-tions of the FIB is presented. The FIB notonly enables the preparation of site-specific samples of uniform thickness, but

it also facilitates the fabrication of lamellaefrom composite samples consisting ofmaterials with very different properties.The strengths of the method as well as theproblems, such as FIB-induced damageand Ga contamination, are illustrated withexamples. The second article, by Uchicet al., describes how the FIB can be used asa tool for three-dimensional characteriza-tion by complementing 2D imaging ormapping with serial sectioning at asubmicron level. The third article, byLangford et al., is organized according tothe general technological area, such asmicroelectronics, photonics, microelectro-mechanical systems, and rapid prototyp-ing. The strengths and limitations of FIBmicro- or nanostructuring are illustratedthrough representative examples, and thearticle ends with a brief summary and alook to the future of FIB nanostructuring.In the fourth and final article, byMoberlyChan et al., advanced topics suchas single-ion implantation, surface mor-phology during ion-induced erosion, andion-induced CVD are discussed.

We hope that this issue of MRS Bulletinwill inform readers about the fundamentalscience and current applications of focusedion beam microscopy and micromachin-ing and give them a sense of the futurepotential of FIB in materials science.

AcknowledgmentsA.M. Minor was supported by the

Director, Office of Science, Office of BasicEnergy Sciences, of the U.S. Departmentof Energy under contract DE-AC02–05CH11231.

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10. M. Nastasi, J.W. Mayer, J.K. Hirvonen, Ion-Solid Interactions: Fundamentals and Applications(Cambridge University Press, Cambridge, UK,1996).11. E. Chason et al., Appl. Phys. Rev. 81, 6514(1997).12. J.S. Williams, J.M. Poate, Ion Implantationand Beam Processing (Academic, Sydney, 1984).13. J. Orloff, M. Utlaut, L. Swanson, HighResolution Focused Ion Beams: FIB and itsApplications (Kluwer Academic, Dordrecht,2002).14. L.A Giannuzzi, F.A. Stevie, Introduction toFocused Ion Beams: Instrumentation, Theory,Techniques, and Practice (Springer, New York,2005).15. J. Melngailis, J. Vac. Sci. Technol., B 5, 469(1987).16. P. Sigmond, Phys. Rev. 184, 383 (1969).17. P. Sigmond, J. Mater. Sci., 8, 1545 (1973).18. J.F. Ziegler, J.P. Biersack, U. Littmark, TheStopping Range of Ions in Solids (Pergamon Press,New York, 1984). The SRIM code is availableonline at www.srim.org (accessed February2007).19. C. Lehrer, L. Frey, S. Petersen, H. Ryssel,J. Vac. Sci. Technol., B 19, 2533 (2001).20. L. Frey, C. Lehrer, H. Ryssel, Appl. Phys.A 76, 1017 (2003).21. X. Xu, A.D. Della Ratta, J. Sosonkina,J. Melngailis, J. Vac. Sci. Technol., B 10, 2675(1992).22. D. Santamore, K. Edinger, J. Orloff,J. Melngailis, J. Vac. Sci. Technol., B 15, 2346(1997).23. B.W. Kempshall et al., J. Vac. Sci. Technol., B19, 749 (2001).24. B.I. Prenitzer et al., Metall. Trans. A 29, 2399(1998).25. T. Ishitani, H. Tsuboi, T. Yaguchi, H. Koike,J. Electron Microsc. 43, 322 (1994).26. E. Chason, M.J. Aziz, Scripta Mater. 49, 953(2003).27. H.X. Qian et al., Appl. Surf. Sci. 240, 140(2005).28. H.H. Chen et al., Science 310, 294 (2005).29. M. Castro, R. Cuerno, L. Vázquez, R. Gago,Phys. Rev. Lett. 94, 016102 (2005).30. C.A. Volkert, E.T. Lilleodden, Philos. Mag.86, 5567 (2006).31. J. Marien, J. Plitzko, R. Spolenak, R. Keller,J. Mayer, J. Microscopy 194, 71 (1999).32. W. Sigle, private communication (2002).33. C.A. Volkert, S. Busch, B. Heiland, G.Dehm, J. Microscopy 214, 208 (2004).34. C.M. Park, J.A. Bain, J. Appl. Phys. 91, 6380(2002).35. T. Ishitani, H. Kaga, J. Electron Microsc. 44,331 (1995).36. H.S. Carlslaw, J.C. Jaeger, Conduction of Heatin Solids (Oxford University Press, Oxford, UK,ed. 2, 1959) p. 264.37. T. Ishitani, Y. Madokoro, M. Nakagawa, K.Ohya, J. Electron Microsc. 51, 207 (2002). ■■






Cynthia A. Volkert Andrew M. Minor David P. Adams Michael J. Aziz Yongqi Fu

Cynthia A. Volkert,Guest Editor for this issueof MRS Bulletin, is aresearch scientist andgroup leader atForschungszentrumKarlsruhe in Germany,where she specializes inmicrostructure andmechanical propertiesstudies of small metalstructures. She received abachelor’s degree inphysics from McGillUniversity and her PhDdegree from HarvardUniversity. Volkert thenspent 10 years working asa staff scientist at BellLaboratories before mov-ing to Germany, first tothe Max Planck Institutefor Metals Research inStuttgart and then toKarlsruhe.

Volkert can be reachedat Institut fürMaterialforschung II,ForschungszentrumKarlsruhe, Postfach 36 40 76021, Karlsruhe,Germany; tel. 49-7247-82-3577, fax 49-4247-82-2347, and e-mail [email protected].

Andrew M. Minor, GuestEditor for this issue ofMRS Bulletin, is a staff sci-entist and principal inves-tigator at the NationalCenter for ElectronMicroscopy at LawrenceBerkeley NationalLaboratory in Berkeley,California. He received abachelor’s degree in eco-nomics and mechanical

engineering from YaleUniversity and MS andPhD degrees in materialsscience and engineeringfrom the University ofCalifornia, Berkeley. Hisresearch group focuses onthe mechanical propertiesof small volumes, in situTEM technique develop-ment, and sample manip-ulation and preparationmethods for electronmicroscopy investigationsof both hard and softmaterials.

Minor can be reachedat Lawrence BerkeleyNational Laboratory, 1Cyclotron Rd., MS 72,Berkeley, CA 94720 USA;tel. 510-495-2749, fax 510-486-5888, and [email protected].

David P. Adams is a dis-tinguished member oftechnical staff at SandiaNational Laboratories.Adams received his bach-elor’s degree in physicsfrom the University ofVirginia and his PhDdegree in materials sci-ence and engineeringfrom the University ofMichigan.

Throughout his techni-cal career, Adams hasbeen involved with thin-film deposition, studies ofmicrostructure and mor-phology evolution duringfilm growth, and materi-als analysis. His currentactivities involve focusedion beams, includingrapid prototyping, devel-opment of in situ metrol-

ogy techniques, investiga-tions of surface morphol-ogy during ionirradiation, and surfacemicromachining. He hasauthored or co-authoredmore than 50 publicationsand is a member of theMaterials ResearchSociety.

Adams can be reachedat Sandia NationalLaboratories, 1515Eubank Blvd. SE, MS1245, Albuquerque, NM,87123 USA; tel. 505-844-8317 and [email protected].

Michael J. Aziz is theGordon McKay Professorof Materials Science atHarvard University. Azizhas made significant con-tributions to the self-organization and kineticsof formation, thermal sta-bility, and decay ofnanoscale structures; thin-film growth by pulsedlaser melting and pulsedlaser deposition; growth,diffusion, and viscousflow in stressed solids;and the kinetics of rapidalloy solidification.

Aziz is a recipient ofthe Presidential YoungInvestigator Award, theONR Young InvestigatorAward, and the SauveurMemorial Lectureship. Healso is a fellow of APSand AAAS.

Aziz can be reached atthe School of Engineeringand Applied Sciences,Harvard University, 29Oxford St., Cambridge,

MA 02138 USA; tel. 617-495-9884 and [email protected].

Yongqi Fu is a researchfellow and leader of thefocused ion beam groupin the PrecisionEngineering andNanotechnology (PEN)Center at NanyangTechnological University(NTU) in Singapore. Hereceived his BEng(mechanical engineering,1988), MSEng (optoelec-tronics, 1994), and PhD(optical engineering,1996) degrees from JilinUniversity, ChangchunUniversity of Science andTechnology, and theChinese Academy ofSciences, respectively. Fuworked in the State KeyLaboratory of AppliedOptics from 1996 to 1998as a postdoctoral fellow.He then worked in thePEN Center at NTU asa research fellow from1998 to 2001. Fu alsoworked in theInnovation inManufacturing Systemsand Technology (IMST)Program of theSingapore–MIT Allianceas a research fellow from2001 to 2005. Fu is aguest professor at theInstitute of Optics andElectronics, ChineseAcademy of Sciences,and has authored morethan 80 peer-reviewedjournal papers and 21conference proceedingpapers.

Fu can be reached atPrecision Engineeringand NanotechnologyCenter, School ofMechanical andAerospace Engineering,Nanyang TechnologicalUniversity, 50 NanyangAve., Singapore 639798;tel. 65-67906336, fax 65-67904674, [email protected], andURL www.ntu.edu.sg/home/yqfu/fyqpage.htm.

Lucille A. Giannuzzi is aproduct marketing engi-neer for focused ion beamand DualBeam™ systemsat FEI Co. in Hillsboro,Oregon. She received herBE and MS degrees fromSUNY–Stony Brook andher PhD degree from thePennsylvania StateUniversity. Giannuzzijoined the University ofCentral Florida in 1994and is founding directorof the MaterialsCharacterization Facility.She joined FEI Co. in2003.

Her research interestsinclude ion–solid interac-tions, grain-boundary dif-fusion and segregation,and structure–propertyrelationships of materialsusing ion and electronbeam microscopy. She hasreceived an NSF CAREERAward and is a memberof numerous societiesincluding the MaterialsResearch Society.Giannuzzi has authoredmore than 100 publica-tions, is an instructor at




the Lehigh MicroscopySchool, and is co-editor ofthe book Introduction toFocused Ion Beams.

Giannuzzi can bereached at FEI Co., 5350NE Dawson Creek Dr.,Hillsboro, OR 97124 USA;tel. 321-663-3806, fax 503-726-7509, and e-mail [email protected].

Jacques Gierak is respon-sible for focused ion beamresearch activity atLaboratoire dePhotonique et deNanostructures (LPN)in Marcoussis, France.He graduated from thePhysics–ElectronicsDepartment atConservatoire Nationaldes Arts et Métiers inParis, where he earnedhis DEA and PhD degreesin instrumentation.Gierak has been involvedin FIB research since 1984and was the coordinatorof the EuropeanCommission–fundedNanoFIB project. In 2004,Gierak was awarded theCNRS Crystal, a prize forexceptional engineeringand technical achieve-ment. He is the mainauthor of several interna-tional CNRS patentsrelated to ion sources, ionoptics, and their control.

Gierak can be reachedat Laboratoire dePhotonique et deNanostructures–CNRS,Route de Nozay, 91460Marcoussis, France; tel.

33-1-69-63-60-75, fax 33-1-69-63-60-06, e-mail [email protected], andURL www.lpn.cnrs.fr/fr/PHYNANO/NanoFIB.php.

Gerhard Hobler is anassociate professor ofsemiconductor electronicsat the Vienna Universityof Technology. Hereceived his Dipl-Ing,PhD, and venia docendidegrees from ViennaUniversity of Technologyin 1985, 1988, and 1997,respectively. From 1996 to1998, Hobler was a visit-ing scientist at BellLaboratories, LucentTechnologies. His currentresearch interests includeatomistic modeling ofion–solid interactionsand thermal processes fol-lowing ion implantation.He has authored morethan 100 papers in thisfield.

Hobler can be reachedat the Institute of SolidState Electronics, ViennaUniversity of Technology,Floragasse 7/362, A-1040Vienna, Austria; tel. 43-1-58801-36233, fax 43-1-58801-36291, and e-mail [email protected].

Lorenz Holzer is a seniorscientist at Empa, theFederal Institute forMaterials Testing andResearch, in Dübendorf,Switzerland. He is leaderof the 3D-Mat Group,

which deals mainly with3D microscopy andimage-based modelingfor quantitativemicrostructure analysis.For the last three years, heworked on FIB tomogra-phy methods for thetopological characteriza-tion of complex granulartextures and porous net-works in cementitiousand ceramic materials.

Holzer can be reachedat 3D-Mat Group, EmpaMaterials Science andTechnology, Dübendorf,Switzerland; tel. 41-44-823-44-90, fax 41-44-823-40-35, and [email protected].

Beverley Inkson is a sen-ior lecturer and head ofthe NanoLAB groupat the Department ofEngineering Materialsat the University ofSheffield. Inksonreceived her MA degreein physics and her PhDdegree in materials sci-ence from the Universityof Cambridge. Her PhDstudies were followed byan Alexander vonHumboldt fellowship atthe Max Planck Institutein Stuttgart, Germany,and a Royal Societyresearch fellowship innanomechanics at theUniversity of Oxford.She is director of theU.K. NanoFIB Networkand director of theRCUK Basic TechnologyProgramme inNanorobotics. Her

current research interestsare centered on thenanomanipulation andmechanical properties ofnanostructured materials,including in situ FIBand TEM nanotesting,3D tomography, NEMS,and nanowire physics.

Inkson can be reachedat the Department ofEngineering Materials,Mappin St., Sheffield, S1 3JD, United Kingdom;tel. 44-114-2225925, and e-mail [email protected].

Takeo Kamino is techni-cal advisor of the NakaApplication Center atHitachi High-Technologies Corp. inJapan. He received hisPhD degree in materialsscience and engineeringat Ibaraki University in1997. Kamino’s currentwork focuses on thedevelopment of a tech-nique for 3D structureobservation of nanomate-rials using a combinationof FIB and high-resolu-tion STEM or TEM. Inaddition, Kamino’sresearch includes thedevelopment of TEMtechniques allowingobservation of atoms during sintering,reaction, and deposition.He has been a memberof the board of directorsof the Japanese Society ofMicroscopy since 2005.

Kamino can be reachedat Naka ApplicationCenter, Hitachi High-

TechnologiesCorporation, 11-1,Ishikawa-cho,Hitachinaka-shi, Ibaraki-ken, 312-0057, Japan; tel. 81-29-354-2970, fax 81-29-354-1971, and e-mail [email protected].

Joachim Mayer is a pro-fessor of physics atRWTH Aachen Univer-sity, where he is head ofthe Central Facility forElectron Microscopy. Hestudied physics at theUniversity of Stuttgartand received his PhDdegree in 1988. Mayerspent two years as a post-doctoral researcher in theMaterials Department atthe University ofCalifornia, Santa Barbara.Afterward, he returned toMax-Planck-Institut fürMetallforschung inStuttgart. In 1999, Mayerjoined RWTH AachenUniversity. In addition tohis work at RWTHAachen, Mayer is co-director of the newlyfounded Ernst RuskaCenter for Microscopyand Spectroscopy withElectrons at the ResearchCenter Jülich, Germany.

Mayer can be reachedat the Central Facility forElectron Microscopy(GFE), RWTH AachenUniversity, Ahornstr. 55, D-52074 Aachen,Germany; tel. 49-241-80-24345, fax 49-241-80-22313, and e-mail [email protected].

Lucille A. Giannuzzi Jacques Gierak Gerhard Hobler Lorenz Holzer Beverley Inkson




Richard M. Langfordworks in the MaterialsScience Centre at theUniversity of Manchester.He received his PhDdegree from the ElectricalEngineering Departmentat Imperial College. Forthe last decade,Langford’s mainresearch interests havebeen in using focusedion beams for nano-engineering and nanofab-rication and developingmethods for samplepreparation for electronmicroscopy.

Langford can bereached at the MaterialsScience Centre, Universityof Manchester,Manchester, UnitedKingdom; tel. 44-161-3065914, fax 41-161-3065912, and [email protected].

Joseph Michael is a dis-tinguished member oftechnical staff in theMaterials and ProcessSciences Center at SandiaNational Laboratories. Hereceived his BS, MS, andPhD degrees in materialsscience and engineeringfrom Lehigh University.Before joining Sandia,Michael was employed asa senior research engineerat Bethlehem Steel’sHomer ResearchLaboratory. His researchinterests involve theapplication of advancedelectron microscopies tothe study of materials.

Recently, Michael hasbeen interested in theuse of focused ion beamtools for the preparationof samples for electronbackscatter diffraction,and for determining the3D structure of materials.He has received theBurton Medal from theMicroscopy Society ofAmerica and theHeinrich Award fromthe Microbeam AnalysisSociety. Michael also haspublished many paperson the application ofelectron microscopy tomaterials.

Michael can be reachedat Sandia NationalLaboratories, MS 0886,PO Box 5800,Albuquerque, NM 87185USA; tel. 505-844-9115and e-mail [email protected].

Warren J. MoberlyChanis a microscopist atLawrence LivermoreNational Laboratory inthe Chemistry, Materials,and Life SciencesDivision. He received hisPhD degree in materialsscience and engineeringfrom Stanford Universityin 1991, and his ScBdegree from BrownUniversity. MoberlyChanhas worked in the infor-mation storage industryat ReadRite, Komag,Quantum, MPI, and SSL.His research interestsinclude thin-film inter-faces and surfaces and theapplication of micro-

scopy, FIB, and spec-troscopy to study theirchemical and mechanicalproperties.

MoberlyChan can bereached at LawrenceLivermore NationalLaboratory, MS L372,7000 East Ave.,Livermore, CA94550–9234 USA; tel. 925-424-2721 and [email protected].

Paul Munroe is a profes-sor of materials scienceand engineering anddirector of the ElectronMicroscope Unit at theUniversity of New SouthWales in Sydney,Australia. He received hisPhD degree from theUniversity ofBirmingham in 1987, andfor his thesis topic hecharacterized themicrostructure ofadvanced titanium alloys.His principal researchinterests includestructure–property rela-tionships in thin-film andcoated materials, and inthe behavior of inter-metallic alloys. Munroereceived the Cowley–Moodie Award from theAustralian Society forMicroscopy andMicroanalysis for“outstanding physical sci-ences electronmicroscopy.” He has pub-lished more than 160 jour-nal papers and serves onthe editorial board ofMicroscopy Research andTechnique.

Munroe can be reachedat the Department ofMaterials Science andEngineering, Universityof New South Wales,Sydney, NSW 2052Australia; tel. 61-2-9385-4435 and [email protected].

Philipp M. Nellen worksat RUAG Aerospace inWallisellen, Switzerland.He received his PhDdegree in physics fromETH Zurich, where healso worked in the OpticsLaboratory at the Instituteof Quantum Electronicson the subject of inte-grated optical chemo- andbiosensors. Afterward, hejoined Empa Switzerland.As a senior scientist atEmpa, his interestsstarted in the field offiber-optical sensor sys-tems for materials andstructures, and the relia-bility of such systems.Following this research,he worked in the field ofFIB micro- and nanostruc-turing of photonic andother devices.

The published workwas done at Electronics/Metrology/ReliabilityLaboratory, Empa, SwissFederal Laboratories forMaterials Testing andResearch, Überlandstrasse129, CH-8600 Dübendorf,Switzerland. Nellen canbe reached by e-mail [email protected].

Edward L. Principe is thefocused ion beam applica-

tions manager within theNanotechnology SystemsDivision of Carl ZeissSMT. He received his PhDdegree in engineering sci-ence from thePennsylvania StateUniversity with researchin the development ofcorrosion-resistant thinfilms. Before joining CarlZeiss, Principe was amember of technical staffat Applied Materials,working on processdevelopment and materi-als characterization across a broad range ofsemiconductor processes.He also worked as a staffscientist at Charles Evansand Associates, specializ-ing in XPS and Augerspectroscopy. Hiscurrent work includesthe development of 3Dmetrology, automatedsample processing, and3D nanofabrication.Principe received theISTA/EDFASOutstanding PaperAward in 2005 and theMicroscopy and Micro-analysis Best PaperAward in 2003. In addi-tion, he has authored twotext chapters on FIBapplications and morethan 20 journal publica-tions.

Principe can bereached by e-mail [email protected].

Thomas Schenkel is astaff scientist in theAccelerator and FusionResearch Division of

Joachim Mayer Richard M. Langford Joseph Michael Warren J. MoberlyChanTakeo Kamino




Lawrence BerkeleyNational Laboratory. Heearned his PhD degree inphysics from the JohannWolfgang Goethe–University of Frankfurtam Main in 1997.Following his postdoc-toral research in theChemistry and MaterialsScience Department atLawrence LivermoreNational Laboratory,

Schenkel joined LBNLin 2000. His currentresearch is focused onthe development andtesting of silicon-basedquantum computerschemes.

Schenkel can bereached at LawrenceBerkeley NationalLaboratory, 1 CyclotronRd., 05R12, Berkeley,CA 94720 USA; and

by e-mail [email protected].

Michael D. Uchic is amaterials research engi-neer in the MetalsDevelopment Group ofthe Air Force ResearchLaboratory, Materialsand ManufacturingDirectorate, at WrightPatterson Air ForceBase. He received his

PhD degree fromStanford University,where he characterizedthe low-temperaturemechanical properties ofthe intermetallic alloyNi3Al. Uchic startedworking with theMetals DevelopmentGroup in 1998, and forthe past five years hisresearch efforts havefocused on the develop-

ment of new experimen-tal methods to rapidlyassess both the micro-structure and mechanicalproperties of aerospacemetals.

Uchic can be reached atAFRL/MLLM, 2230 10thSt., Wright Patterson AFB, OH 45433 USA; tel. 937-255-4784 and [email protected]. ■■

Paul Munroe Philipp M. Nellen Edward L. Principe Thomas Schenkel Michael D. Uchic


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