Yao N. Focused Ion Beam Systems: Basics and Applications

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4 µm

Vector scan

Raster

Etching Deposition

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Figure 14.16 (a) Array of 5 · 5 circles, (b) results of etching and depo sition.

-scan signal

Blanking signal

Waveforms

Top view

Cross section

Figure 14.17 3D shaping.

Focused ion beam systems368

14.3 Role of FIB in nanotechnology

14.3.1 Nanotechnology

Figure 14.18 shows that to establish nanotechnology as an industrial product,

technology to create structures at the order of nanometers must be effectively

fused with mass production technology. For example, information available

on Intel’s home page shows the realization of manufacturing microscopic

devices by applying nanotechnology to integrated circuit manufacturing

technology, and by technological trends predicted by Moore’s law [7]. In

considering the role of the FIB tool in the development of nanotechnology,

the FIB tool can create structures of the order of micrometers to nanometers,

and since creating a photo mask is not required, the work takes compara-

tively less time resulting in an extremely useful tool.

14.3.2 Etching process

The biggest features of processing by FIB use the same ion beam in obser-

vation and processing. As shown in Figure 14.5, the observation region is

sputter etched as observation continues. This function lets you accurately and

precisely process extremely microscopic regions.

Microscopic etching process

In recent years, research into the shapes of electrodes with extremely small gaps

has greatly advanced. Objectives are many, including trying to make new

elements and trying to observe the types of phenomenon that occur in gaps at an

order of nanometers.

One experimental result [8] gives an example of a 5 nm width gap formed

by applying FIBs. Here the objective is to measure the electric properties of

high polymer materials at molecular levels using a manufactured electrode.

Mass production

Photo lithography

Prototype

Developing

New material

Miniaturization

Integration

Commercialization

Nanotechnology

Fusion

Figure 14.18 Nanotechnology as an indust rial product.

Focused ion beam systems as a multifunctional tool for nanotechnology 369

At the time the gap is made, the ﬁrst step is to form a 12 nm wide gap in Ti by

sputter etching with the FIB, and the second step is milling of Ti on the mask

with Ar and etching the Au.

An SMI9200 (JFIB2300) FIB tool of SII with 7 nm secondary electron

resolution was used in this process. The latest tool was improved to have a

secondary electron resolution of 4 nm. In the case of the ion beam, the sec-

ondary electron resolution is almost the same as the beam diameter. This

performance has allowed even narrower gaps to be formed, compared with the

SMI9200.

Ordinarily, when expressing process performance with the FIB, there is a lot

of dispute over the maximum current and maximum current density because

of the desire to increase process throughput. However, if using the FIB tool as

an experimental tool for nanotechnology, using a beam current with a beam

diameter of less than 10 nm is essential. Processing microscopic areas precisely

and rapidly is required by setting a beam current that is optimized for making

structures.

Etching using graphic information

Processing must be performed as you monitor process conditions without

regard to size.

Figure 14.19 shows an example of a mask repair. The mask is made from a

light-penetrating glass board and a shading ﬁlm such as light-shading chrome

ﬁlm. Figure 14.19 shows an example of white defects where chrome originally

should have been, but are now missing. In this case, carbon is deposited at

the white defect area using the FIB deposition function [9].

In the case of a mask repair, you must avoid causing damage to the light

penetrating part by irradiating it with the ion beam more than is necessary.

The mask stage locates a

defect position using

the inspection system

coordinate and grabs

the defect ima

The operation

software automatically

enhances

the edge signal.

The software defines the

repairing position from

the processed image, and adds

the repair area

to the SED ima

Figure 14.19 An example of a mask repair.

Focused ion beam systems370

The ion beam must not irradiate the unnecessary part to prevent damage

being caused to the light penetrating glass. Consequently, graphic informa-

tion is used. In this example, a secondary ion detector is used in the detector.

Secondary ions are analyzed and the image is made binary from the presence

of chrome. Ion beams irradiate and carbon ﬁlm is formed at the spot where

chrome should originally exist within the binary image; in other words,

only at the white defect area. Figure 14.20 shows the results of two types of

mask repair observed by an atomic force microscope (AFM). Both were

repaired using the FIB deposition function. A Cr binary mask is a type of

conventional mask, whereas a MoSi mask is a type of phase shift mask.

The technology developed for mask repair is explained in the following. This

technology makes use of graphical information to ensure precise processing.

As shown in Figure 14.9, it is difﬁcult to obtain a ﬂat bottom after Cu

milling. To improve the ﬂatness of the bottom, graphic information was used.

The lower insulating ﬁlm can be seen as etching of the Cu wire progresses.

Figure 14.21 shows the secondary electron image of Cu during the process.

The bright area is Cu and the dark area is SiO

Observation of the processed region during processing at a ﬁxed period

seeks a binary image that is separated into bright regions and dark regions.

This binary image corresponds to whether there is Cu in the wire. Bitmap and

process data ﬁles are created from the binary image and ion beam irradiation

is performed by dot blanking scanning (Figure 14.22).

Observations are successively done during the process, bitmap and process

data ﬁles are updated, and the process advances.

Observation performed by secondary electrons has channeling contrast

that relies on grain shape. When creating a binary image based on the image,

100 [nm]0

[µm]

(a) (b)

100 [nm]0

[µm]

Figure 14.20 AFM image of a mask repair. (a) Binary deposition on Cr,

(b) deposition on MoSi.

Focused ion beam systems as a multifunctional tool for nanotechnology 371

areas having Cu can no longer be correctly recognized; therefore, secondary

ions are used. Images by secondary ions are contrast images that rely on the

quality of the material. Having been affected by channeling contrast, Cu

regions and regions without Cu cannot be discriminated (Figure 14.23).

Figure 14.24 shows an example of a processed Cu wire using a secondary

ion image. It can be veriﬁed that only the Cu is being etched as the process

progresses.

Figure 14.25 introduces an example of a process implemented based on

bitmap and process data. A process is terminated when the entire processed

region becomes bright showing the insulation. Decelerated etching by water

is not used in this process. Remarkable improvement is shown compared

with the example (without gas) introduced in Figure 14.9.

Finally, the ﬁnishing process is done by decelerated etching using water

from the condition shown in Figure 14.25. Figure 14.26 shows that the Cu

Figure 14.22 Example of bitmap processed data.

SiO

Figure 14.21 Secondary electron image while processing Cu. Only the center

area has been processed.

Focused ion beam systems372

was cleanly removed. Thus, precision processing can be performed by getting

feedback from image information.

14.3.3 3D deposition

The ﬁrst commercialized application of an FIB was mask repair and circuit

edit using deposition. Both of them use deposition in two dimensions.

(a) (b)

Figure 14.23 (a) Secondary electron and (b) secondary ion images during Cu

milling.

SiO

(a) (b)

Figure 14.24 Change in secondary ion image during Cu processing.

(a) Before etching, (b) after etching. The processed region is the center

area, the dark area is Cu, and the bright area is SiO

(a) (b) (c)

Figure 14.25 Processing using image information, with secondary ion (a),

secondary electron (b), and secondary electron tilted (c).

Focused ion beam systems as a multifunctional tool for nanotechnology 373

During the 1990s, research into three-dimensional deposition was reported.

The initial report was on a standing pillar, but the objective was to evaluate

the stability of the ion beam optic system by making three-dimensional

shapes. Afterwards, the performance and reliability of FIBs drastically

improved and three-dimensional shapes could be made stably.

Figure 14.27 shows an example of a micrometer sized wineglass made by 3D

deposition from carbon deposition developed by NEC, University of Hyogo,

and SII [10,11].

This 3D deposition must be performed more uniformly and with higher

gas density in the ion beam irradiation region than with 2D deposition.

Figure 14.28 shows this process diagrammatically.

A high density, uniform gas is supplied from the gas injector to the area of ion

beam irradiation. When forming a pillar, the ion beam continuously irradiated

the same position to produce the 3D structure. Overhanging shapes can be

achieved by widening the irradiation range in the horizontal direction. The wine

(a) (b)

Figure 14.26 Secondary electron image after the ﬁnishing process by

decelerated etching. (a) Top view; (b) bird’s-eye view.

2.75 µm

Figure 14.27 Example of 3D deposition. Material: carbon, process time ¼

600 s.

Focused ion beam systems374

glass was made by drawing a circle with a small radius by vector scanning and

then extending the radius.

Incidentally, when ion beams are irradiated to the surface of a specimen,

the surface is etched by ion beams. The deposition rate must be bigger than

the etching rate. Usually, the ion beam current for deposition is set low to

achieve a low etching rate.

3D shaping using 3D-CAD data

Figure 14.29 shows an example using 3D-CAD data for 3D deposition. To

make this shape, 100 horizontal layers of slice data from a 3D-CAD were

created in .bmp format, and 100 carbon deposition ﬁlm layers were created

Melting point: 99˚C

Boiling point: 340˚C

Diamond-like carbon (DLC) pillar

Phenanthrene gas

Decomposition of

Adsorbed molecule

Secondary

electrons

Figure 14.28 The 3D deposition process.

(3D-CAD)

30 kV, Ga

, 9 pA

Bitmap: 100 sheets

Sample: Si wafer

2 µm

Figure 14.29 Nano -toilet produced using 3D-CAD data for 3D deposition.

Focused ion beam systems as a multifunctional tool for nanotechnology 375

in order by the dot blanking scan method, beginning from the lowest layer

(Figure 14.30).

We were able to verify from our experimental results that the ion beam mold

method could be implemented in the same way as the light mold method, by

ion beam induced deposition. In order to realize more precise shapes in the

future, the following research needs to be pursued [12]:

1. Technology that corrects shape change from etching that progresses at the same

time as deposition ﬁlm proximity deposition.

2. Establish a deposition data producing algorithm for realizing structures pushed

out at location s that don’t have a base.

14.3.4 3D Etching

Figure 14.31 shows examples of lens shapes made by etching glass. In these

examples, 3D-CAD data were used. In a different way from that used for

deposition, space other than the manufactured object at the process space

is deﬁned as etching space and creates .bmp ﬁles. In the examples in

Figure 14.31, sputter etching using dot blanking scanning progresses from

the top surface layer. This time, gas accelerated etching is used in order to

accurately realize speciﬁed shapes. When the redeposited material from

sputter etching remains in the process area, the gallium ion for the original

shape production is used to remove the redeposited material, and as a result

the intended shaped can no longer be realized. Thus, in the actual imple-

mentation, we try not to generate redeposited material using XeF

gas. The

results are that there is no effect from redeposition material and the intended

shape can be accurately reproduced.

Slicing to make

100 sheets of

the bitmap

data

Figure 14.30 3D data producing process.

Focused ion beam systems376

14.4 Unfolding of nanotechnology

This section outlines applications in micro-machining and nanotechnology of

microscopic 3D structure production technology that uses all the types of

process technology introduced in the previous chapters.

14.4.1 TEM sample preparation

The needs for observation, measurement, and analysis of ultra-microscopic

shapes are dramatically increasing together with the development of nano-

technology. In particular, there are increasing demands being made of obser-

vations by the transmission electron microscope (TEM). TEM is a tool that

irradiates accelerated electrons at high voltages of several 100 kV or greater on

samples with a thickness of 100 nm, and observes structures within the lamella

at atomic levels of resolution by detecting transmitted electrons. TEM is a

technology that already has a history going back several decades, but users

must make thin lamellae to observe by TEM. It takes more than one day for a

skilled technician to make a thin lamella using chemical polishing. With this

method, a speciﬁed spot on a miniaturized integrated circuit cannot be cut as a

speciﬁcation.

However, Kirk et al.[13] developed a practical method of using FIB in

TEM specimen production. Automation has progressed, and, in the latest

report, TEM specimen production exceeding 100 specimens per day was

enabled by an FIB tool and system consisting of one microscope each with a

manipulator using the lift-out method (Figure 14.32)[14].

Beam position stability

The thickness of a lamella specimen is commonly 100 nm. Lamellae of

thicknesses of 40 nm or less are looked at depending upon the material and

(a) (b)

Figure 14.31 Lens shaped glass produced using 3D-CAD data. (a) Converging

lens, (b) concave lens.

Focused ion beam systems as a multifunctional tool for nanotechnology 377