Yao N. Focused Ion Beam Systems: Basics and Applications

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stage is tilted and the cutting plane is viewed at an angle dictated by the

angular separation between the FIB and SEM column. The image data are

properly tilt compensated during the acquisition to correct for the geometric

tilt. The image data may also be adjusted using electronic beam shift during

the acquisition in order to compensate for the translational shift in the SEM

image. Automatic image registration is also part of data acquisition software.

Image processing may involve contrast enhancement, segmentation,

threshold operations, or any other combination of standard image processing

steps. For the results presented in this chapter image processing was not

extensive and consisted of contrast adjustment or pass ﬁlters to facilitate

transparency mapping. However, in future more sophisticated image pro-

cessing will likely be employed to develop quantitative metrology applica-

tions as the ﬁeld of 3D FIB-SEM nanotomography continues to emerge.

A variety of commercial software and freeware is available to complete 3D

reconstructions that vary in sophistication and capability, including the

integrated Smart3D software. Reconstructions of the type depicted on the

following pages can be processed within one hour. The quality and ease of

data processing is strongly dependent upon the quality of the original image

data volume. Strong contrast and good signal intensity translate into an

easily processed and high quality data set.

6.7 High density quantitative FIB-SEM nanotomography results

A series of examples follow that demonstrate the application of FIB-SEM 3D

nanotomography including real-time data acquisition during the milling

process. There is an inherent challenge capturing the experience of a dynamic

process in the static format of a text. The reader should bear in mind that

one can interrogate the data interactively including the ability to rotate the

object freely, zoom in or out and even generate a ‘‘ﬂy-through’’ path on the

region of interest. It is common to animate the ﬁnal results for presentation

purposes.

6.7.1 FIB-SEM 3D reconstruction of a superconducting thin ﬁlm

Figure 6.8 depicts a High-Tc superconductor thin ﬁlm with second phases

(dark areas in cross section). The top panel is a frame from the original AVI

capture and the second panel is the volumetric reconstruction with selective

transparency applied to display only the second phase material. This example

demonstrates the ability to investigate a very complex and irregular structure.

Interpolative schemes are generally not necessary due to the high data density

Focused ion beam systems168

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(b)

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Figure 6.8 3D FIB-SEM nanotomographic reconstruction of a High-Tc

superconductor thin ﬁlm with second phases (dark areas in cross section).

Panel (a) is a frame from the original AVI capture and the panel (b) depicts

the volumetric reconstruction with selective transparency applied to

highlight the second phase material. Common features in each image are

marked by the arrows. Panel (c) is a different view but also shows a different

section plane from the full transparen cy. The section plane is indicated by

the dashed marker. Panel (d) is a transparency section plane close to the

bottom of the reconstruction volume and highlights the nucleation density

of second phases along the interface. (Sample courtesy of Dean Miller and

Jon Hiller, Argonne National Laboratory.)

High-density FIB-SEM 3D nanotomography 169

and a user speciﬁed slice thickness in the typical range of 5–20 nm. The solid

reconstruction (no transparency applied) is not shown. In addition, it is

possible to ‘‘slice and dice’’ either the solid reconstruction or data with

applied transparency any way desired, allowing considerable freedom in the

analysis and study of the subject. This capability is illustrated through the

third and fourth panels of Figure 6.8 where the transparency data are taken

at two different x–z planes in the transparency. This particular example was

completed from 100 image frames and covered a distance of approximately

0.75 mminthey-axis direction.

Using the same live imaging techniques, method of quantiﬁcation, and

equipment as described here a team of researchers have applied volumetric

analysis to a solid oxide fuel cell sample [16]. They applied the 3D recon-

struction to determine volumetric fractions of the material constituents and

porosity. In addition, with aid of an application speciﬁc code the lengths of

contiguous three phase boundaries in the volume and the connectivity of sub

phases were mapped in the ﬁrst volumetric analysis of its kind. In this way

quantitative correlation of microstructure with electrochemical performance

was enabled via a quantitative FIB-SEM 3D reconstruction. This example

points to the potential of the technique and future directions and highlights

application of the method beyond visualization.

6.7.2 FIB-SE 3D reconstruction of a second phase in a stainless

steel heat affected zone

In Figure 6.9 the top two panels depict two images extracted from the ori-

ginal data stack. The precipitate phase is represented by the dark features in

the cross section and provided strong contrast relative to the bright intensity

of the matrix. The sample was embedded in epoxy and the top surface was

polished prior to FIB-SEM reconstruction. A platinum layer was deposited

on the surface to protect the portion of the structure at the surface. The

ﬁducial marks for quantiﬁcation (not shown) were also etched into the pla-

tinum layer outside the ﬁeld of view. Again, the FIB-SEM nanotomographic

reconstruction faithfully reproduces details in the original structure. The

reconstruction is 563 · 135 pixels and consists of 200 frames over a y-axis

linear dimension of approximately 1.4 mm to yield a 4 nm slice thickness

encompassing a volume of approximately 25 mm

. Growth, shape, and

nucleation parameters can thus be studied in three dimensions. Several data

sets were obtained from this material at different sections of the weld. The

different shapes and structures of the phases frozen into the material reﬂected

Focused ion beam systems170

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Figure 6.9 3D FIB-SEM reconst ruction with transparency applie d to

highlight phases formed in a heat affected zone of a stainless steel weld. The

top two images (a, b) are frames extracted from the original movie .

Reconstruction views are shown in (c) and (d). A common feature detail is

identiﬁed by the arrows. Axes units are micrometers in (d). (Sample courtesy

of Mahesh Chaturvedi, University of Manitoba.)

High-density FIB-SEM 3D nanotomography 171

the thermal histories from the various regions of the weld. Quantiﬁcation of

all three axes has been applied to this volume, as shown in the fourth panel.

6.7.3. Stereolithographic printing of the second phase

in stainless steel HAZ

In cooperation with the State University of New York, Stony Brook

(SUNYSB) the ﬁrst 3D stereolithographic print was produced from an

FIB-SEM 3D tomography dataset. The 3D model shown in Figure 6.10 was

produced from the data set shown in Figure 6.9. Originally approximately

10 mm in length the physical model measures over 25 cm to allow a virtual

nanoscale to macroscale conversion. Using a routine to convert the original

intensity matrix into a format compatible with the 3D printer (STL format)

it was a fairly straightforward process to produce a quantitative three-

dimensional solid model. Following a similar approach it is also possible to

scale replicate an object using the deposition capabilities within the CrossBeam.

Figure 6.10 The ﬁrst 3D stereolithographic print of an FIB-SEM nanotomo-

graphic reconstruction. The original object dimension was less than 10 mm

across while the macroscale model of that original object is over 10 inches in

length and repres ents the same structure shown in Figure 6.9. The project to

convert one of the 3D nanotomography data sets into a stereolithography

format (STL) for printing was motivated by Dr. Jim Quinn at SUNY, Stony

Brook. Dr. Quinn produced the ﬁrst examples in his laboratory, including

the one shown. The ﬁle translation routine into the STL format was

completed by Peter Sobol of Monona Analytical Services in Madison,

Wisconsin.

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Integral software on the CrossBeam platform allows the user to reslice the

3D reconstruction following data reduction and then rebuild the object at a

chosen scale layer by layer using any of the selected deposition materials,

including metals, oxides or carbon precursors. A potentially interesting

application of this technology is to scale replicate pattern templates using

FIB-SEM reconstructions produced from natural structures. Objects could

range from diatoms to the interlaced ladder-like structure of the cross section

from a butterﬂy’s wing. The stereolithographic 3D models also make lovely

bookends.

6.7.4 3D reconstruction of a multi-layer semiconductor device

Figure 6.11 depicts a multi-layer semiconductor device with copper inter-

connects. The top panel is a cropped portion of a frame from the original

movie. Voltage contrast is apparent in the SEM image data where some

interconnects are bright while others are dark. Since these reconstructions

are intensity-based, the dark interconnects do not display clearly throughout

the selective transparency volume. Collection of a BSE image is one

approach to eliminate the voltage contrast when desired. The second and

third panels represent solid reconstructions depicting different section planes.

Recall that the top surfaces are planes perpendicular to the cutting plane.

Note the detail of the copper grain structure in the third panel highlighted by

the arrow. It is possible to trace the copper grain structure throughout the

volume.

FIB-EDS 3D reconstruction of a multi-layer semiconductor device

Figure 6.12 depicts an FIB-EDS reconstruction of the same device shown in

Figure 6.11. The information vector in this reconstruction is associated with

X-ray intensity data for the copper L line. These data were acquired at 5 kV

in order to excite the Cu

X-ray. The reconstruction is based upon 18 data

slices and has an inherently lower resolution than the FIB-SE data due to the

larger analytical volume associated with the X-ray signal at 5 kV. The key

beneﬁt of FIB-EDS is the opportunity to combine high-resolution image data

with compositional information.

6.7.5 FIB-BSE 3D reconstruction using the in-lens EsB

backscatter detector

Figure 6.13 is an FIB-BSE nanotomographic reconstruction of a multi-layer

semiconductor device. Figure 6.13(a) shows a single frame from the image

High-density FIB-SEM 3D nanotomography 173

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Figure 6.11 3D FIB-SEM reconstruction of a multi-layer semiconductor

device. Panel (a) is a cropped frame extracted from the original AVI movie.

Panels (b) and (c) are solid 3D reconstructions sectioned along different

planes and perpendicular to the FIB cutting plane. Note the detail in the

cross section, particularly in the panel (c), where the copper grains are

clearly visible (marked by the arrow). Note also the voltage contrast seen in

the image. Panel (d) presents the volume reconstruction with transparency

applied to highlight the copper interconnects. (Sample courtesy of Bernie

Levine, SUNY at Albany Nanotechnology Center, College of Nanoscale

Science & Engineering.)

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data stack showing the total cross section, which extends approximately

40 m m in width. The data set was collected using a 20 pA milling current

and acquired in less than 2 hours. The highlight area in Figure 6.13(a) is the

sub-volume from which the 3D reconstruction shown in Figure 6.13(b) and

350 frames with a 15 nm slice thickness encompassing a volume of 22 m m ·

3.5 mm · 4 mminthex, y,andz-axes respectively. The data were acquired using

the in-lens backscatter (EsB) at a primary voltage of 0.8 kV. The brightest

contrast regions in the EsB image stack, such as the eight areas seen in Figure

6.13(a) correspond to the via material. The next brightest contrast is from the

metal interconnects and the lowest contrast level is from the interlayer

dielectric. In the reconstructions in Figure 6.13(b) and upper image in Figure

6.13(c) the via material is mapped to blue while the interconnects are mapped

to red. In Figure 6.13(b) transparency mapping is applied to remove the

(a)

(b)

Figu re 6.12 FIB-EDS reconst ruction of the struc ture sh own in Figure 6.11 .

Ori ginal EDS da ta maps were acqu ired by James Evertsen, SUNY at

Albany Nanotechnology Center using a PGT EDS spectrometer.

High-density FIB-SEM 3D nanotomography 175

interlayer dielectric completely. Upper panel in Figure 6. 13 (c) is a three color

composite with a lower degree of transparency applied to the dielectric (green)

to provide additional depth contrast. The view in the upper image of Figure

6.13(b) is at positive elevation viewed from the rear of the volume with respect

to the orientation in Figure 6.13(a) while the lower image is a negative ele-

vation view (bottom view) as seen from the front. The lower image in Figure

6.13(c) is the same view as the upper image in Figure 6.1 3( c ) r ep re se nt ed a s a n

isoclinic surface that maps the 204 intensity level from the 0–255 range in the

data and thereby shows exclusively the via material throughout the volume.

The image in Figure 6. 13 (a) represents a single plane of the data stack that

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Figure 6.13 FIB-BSE 3D nanotomography of a multi-layer semiconductor

device using in-lens EsB detection. The backscatter image data stack was

captured using a primary voltage of 0.8 kV. The EsB detector produces

high-resolution z-contrast, which is favorable for separating different

materials in the 3D reconstruction while suppress ing voltage contrast and

edge enhanced contrast effects.

Focused ion beam systems176

bisects the approximate center of the eight via structures seen along the back

plane region of the isoclinic view in Figure 6. 13 (c ). T he a rr ows i de nt if y a

corresponding structure in each image. Figure 6.14 provides another example

of FIB-BSE reconstruction representing a BW of 65 nm dual damascene

structures. Various views in the ﬁgure illustrate that volume reconstructions

can be combined with a surface mesh mapped to speciﬁc intensity values.

6.7.6 FIB-EBSD

The EBSD technique is too rich in information and complexity to give a full

accounting in the scope of this text. A general overview is given to facilitate

presentation of the FIB-EBSD methodology and results. The interested reader

should consult references for further study [17]. In the EBSD technique an

incident electron beam forms an angle of approximately 20



with the sample

plane, as shown in Figure 6. 15 . The beam voltage is generally 15–20 kV to

obtain a properly scaled pattern. The glancing angle geometry of the electron

beam facilitates production of strong intensity electron channeling patterns

(commonly called electron backscatter diffraction patterns) which escape from

the near surface region of the sample. The projected patterns are captured onto

a phosphor screen. The EBSD pattern consists of multiple pairs of Kikuchi

lines. Each pair forms a Kikuchi band that corresponds to a speciﬁc plane

Figure 6.14 FIB-BSE 3D nanotomography example from a 65 nm node dual

damascene structure. Note that a volume reconstruction can be completed

by a surface mesh over the same region of interest. Several reconstructions

also can be combined from different sub-volumes within the same dataset.

High-density FIB-SEM 3D nanotomography 177