Metrology and standard which underpin the development of nano technology
Toshiyuki Takatsuji1
1

National Metrology Institute of Japan / AIST, Tsukuba, JapanAbstract – No one doubts both metrology and standard are essential in the development of nano technology. There are two standards,
i.e. industrial standard and measurement standard, and they are in a complimentary relationship thus referring to the other. In addition,
two kinds of standards are useless unless appropriate measurement techniques and their traceability are established. In this article, therelationship among the industrial and measurement standards, measurement techniques and traceability is explained following theirnecessity for the development of nano technology. We can conclude metrologists can play an important role in the development ofnano technology.
Key Words: Nano metrology, traceability, measurement standard, industrial standard

1. Importance of standard in nano technology

systems; therefore its effective use is quite profitable.

It is beyond discussion that nano technology underpins current

In the traceability system defined by the JCSS, the combination ofsociety and no one questions that metrology supports nano

the optical frequency comb and the atomic clock synchronized withtechnology.

UTC (Universal Time, Coordinated) owned by NMIJ is located at theWe can easily point out typical examples. Metrology makes animportant role for the quality control of production process and thetop level, i.e. designated as a primary standard, and all other
instruments are linked below in hierarchy system like a pyramid.

evaluation of functions of nano products. When we assess theLet us introduce one useful topic for length metrologists. The

influence of nano materials for human bodies and environment, size

frequencies of stabilized lasers whose frequencies are locked with themeasurement of nano products is essential. In addition improvement

absorption lines of atoms are intrinsically fixed and hence knownof functions of nano products directly leads energy saving.

without calibrations. Such measurement standards which takeadvantage of physical phenomena and do not need calibrations are

2. Industrial standard and measurement standard

called intrinsic standards.

Before starting the consideration of nano metrology, we are going

Intrinsic laser frequency standards are approved by Committee ofto review industrial standard, measurement standard, and theirInternational Weights and Measures (CIPM) and listed in the table bydifferences. They are often confused with each other.

the name of MeP (Mise en pratique).1) An unstabilized He-Ne laser at

Concisely speaking industrial standards are documents such as ISO

633 nm has been registered in MeP, which is the most commonly usedand JIS, so that it is also called document standards. Common

for length measurements.2) It means the He-Ne laser at 633 nm isagreements which stipulate the specifications of products or testingintrinsically traceable without calibration as far as they are emitting

procedures are documented.

light. (As far as JCSS is concerned, the He-Ne laser at 633 nm stillOn the other hand, measurement standards are the definitions ofneeds calibration because the frequency comb owned by NMIJ is onlyunits and their realization. Measurement standards are needed to

one designated primary standard and all length measuring instrument

secure the correctness of the results of measurements. For thisin JCSS system shall be calibrated and traceable to the primary

purpose, in addition to the definition of units the traceability system isstandard.)

indispensable.
These two standards are completely different, but in practical use
they are closely related and refereed each other.

2.2. Industrial standards
There are two categories of industrial standards. One is a productstandard which defines specifications of industrial products, such as

2.1. Measurement standards
Measuring instruments which are used in many occasions inindustries should be calibrated by higher level measuring instruments.

size, shape, characteristics, and so on. The other category is aprocedure which defines testing or measuring method of industrialproducts.

These higher level measuring instruments also should be calibrated by

The most famous industrial standard is ISO standard. ISO standards

much higher level measuring instruments. The system in which

are being discussed in Technical Committees (TC), each of which istracing this calibration chain leads to national or international

responsible for a specific technical area. Technical committees which

standards is called traceability (system).

are relevant to nano technology have been existed, such as TC 201

In Japan there is JCSS (Japan Calibration Service System)(Surface Chemical Analysis) and TC 202 (Microbeam Analysis). In

regulated by the Measurement Law. JCSS is not a sole accreditation

addition to them, TC 229 (Nanotechnologies) has been founded which

system and there are many other accreditation systems by whichis responsible for nano technology and has received worldwide

traceability is secured. JCSS, however, is one of the most reliableattention. TC 229 will be explained later.

methods since the physical interactions or phenomena occurred
3. Problems raised in nano metrology

between the probe and the surfaces of the measuring objects are

There are a lot of varieties of length measuring instruments fordifferent sizes of measuring objects. The most high resolution
instruments are transmission electron microscopes (TEM) anddifferent. This fact has been considered the largest problem innano metrology. Examples will be shown in the next section.
4)

Ambiguous definition of the measurandscanning probe microscopes (SPM). These instruments enable toEven if the measurands (quantity to be measured) are called theobserve objects with sub-nanometer resolution, even atoms can besame for different measuring methods, definitions of theobserved.

measurands are not always the same. There is a posssiblity to

By the way, the practical length standard is a laser wavelength. It

observe different physical properties.

was supposed to be very short for a long time, however, compared tothe size treated in the current nano technology it is not so long anymore. To keep the traceability of nano metrology from the primary
standard, i.e. laser wavelength, the wavelength must be subdivided. It

4. Necessity of advanced measuring technology
The fact that different results are obtained by different measuringmethods is inevitable in most cases nowadays.

means the phases of light waves must be determined. Normally thisLet us see one example. Nano particles are one of the most typicaltask is performed by using interferometers, but the accuracy of phaseand commonly used nano products which are very versatile in manydetection is not so high due to several reasons.

industrial areas. There are many measuring principles and instruments

Although I wrote atoms can be observed, only ‘observations’ can beto measure the particle size, such as SEM (Scanning Electronpossible but ‘measurements’ are impossible. In fact, accuracy of nanoMicroscopy), TEM (Transmission Electron Microscopy), SPM

metrology is not always so high than it is thought to be (correctly(Scanning Probe Microscopy), DLS (Dynamic Light Scattering),

speaking, the term ‘uncertainty’ should be used instead of ‘accuracy’,

SAXS (Small Angle X-ray Scattering), DMA (Dynamic Mobility

but two words are used as almost the same meaning hereafter). OnlyAnalysis), and so on. However different instruments are not always

the resolution is extremely high. It is often the case with nanobring the same result. Figure 1 shows the result of an international

metrology that the reliable digits of measurement results are only twocomparison initiated by European Metrology Research Programand in extreme cases only one.

(EMRP).

When nano metrology is actually performed, one can see theAnother example is the line width measurement of nano scales.

instability of measurement results. Several reasons for this can be

There are three common methods for measuring the line width, SEM,considered.

AFM, and an optical probe microscope. In SEM measurement,

1)

Low quality of measuring objects

secondary electrons scatter at the edges of the lines. When theAs the measuring objects are extremely small, fabricating theelectron beam scans perpendicular to the line and the beam crosses

objects as they have been designed is difficult. Consequently

the edge, the signal is observed larger by the scattering effect. In AFM

different measurement results can be obtained even if themeasurement, the convolution of the tip form of the probe and themeasuring position is slightly shifted.

object is observed. To retrieve the true form of the object, a2)

Environmental effectde-convolution calculation is necessary. In optical probe measurement,

Air turbulence causes unstable measurement results forthe spot size of the optical probe is far larger than the size of theinterferometricmay

object; hence a simple geometrical optics theory cannot be applied.

contaminate the surface of measuring objects thus resulting inFigure 2 explains the bias observed between SEM and AFM

unstable measurement results.

measurements.

3)

measurements,forexample.

Dusts

Difference of physical phenomena occurs between themeasuring object and the probe

Measurement results can be different for different measuring

Fig. 1 Result of the nano particle comparison (copied fromthe presentation by Dr. Thalmann in CCL Nano Symposium2009 in A*Star Singapore)Fig. 2 Line width bias correction between AFM and SEM

To overcome this difficulty, development of accurate and stablemeasurement techniques is essential and this task is required for thescientists researching on precision engineering primarily metrology.
In the process to pursue this task, we may go back to basic researches
to investigate on fundamental physical phenomena.

6. Measurement standards provided by NMIJ
Two calibration services in nano metrology developed and supplied
by NMIJ are shown here.
The first one is one dimensional nano scale (1-D gratings). In theproduction process of semiconductors, critical dimension scanning

In the discussion of the Consultative Committee for Length (CCL)

electron microscopes (CD-SEM) are often used. The accuracy ofof International Committee of Weight and Measures (CIPM), alength measurement is critical to improve the quality and the yieldsuggestive comment was given which impressed me deeply.

rate of semiconductors. CD-SEMs, however, are not able to secure the‘Currently, different measurement results can be obtained by different

traceability of length measurements by itself. For this purpose,measurement methods in nano metrology. It is caused by the lack ofCD-SEMs are equipped with calibrated 1-D gratings on the side of theour knowledge for natural phenomena. To diminish this difference isspecimen tables and the nano scales are routinely measured so that thethe mission given for metrologists.’

traceability can be secured.

5. Necessity of measurement standard

approximately 70 %. This fact implies the 1-D gratings are of crucial

The world market share of CD-SEM by Japanese manufacturers is
Development of advanced measurement technology is not a goal. It

importance. A grating of 240 nm pitch has been used for many years

is necessary to confirm if the measuring technology developed is valid

for this purpose and recently 100 nm pitch grating is used. As theand the measurement that users are actually performing is correct.

process rule of semiconductors is becoming smaller, 100 nm grating isIf calibration services or certified reference materials (CRM) are

no more sufficient. NMIJ has completed the development of a 25 nm

available, users can check the correctness of their own measurements

grating which will be used for the production of next generation

easily. In case there is a bias between the measurement value and thesemiconductors. The history and roadmap of nano scale development

calibrated value, users can compensate this bias by themselves; theis shown in Fig. 3. The nano scales have been prepared well in

usefulness of the calibration services and CRM are obvious.

advance than expected by International Technology Roadmap for

In response to these requirements, AIST is providing various

Semiconductors (ITRS).

calibration services and selling CRM. In the next section, a few

The 25 nm scale is so small to make even by the electron beam

examples will be shown. A strategic plan to expand the scope of thelithography. We have invented a tricky manufacturing process to makecalibration services and CRMs has been made. Since it is a mission

nano scales very easily as follows.4) First, fabricate supperlatticefor AIST to satisfy the demands from industrial users, any requests

structure by layer-by-layer deposition by molecular beam epitaxy

and opinions for the measurement standard maintenance plan are(MBE) (for GaAs/InGaP suparlattice) or sputtering deposition withalways welcome.

alternative target change (for Si/SiO2 super lattice) so that two

Another tool to encourage various stakeholders to collaborate is thedifferent materials are layered several ten times. Second, cleave theStrategic Technology Map published by the Ministry of Economy,

supperlattice. Finally, etch the cleaved face to remove one material

Trade and Industry (METI).3) NMIJ is acting as a secretariat toselectively and a comb shape nano scale can be fabricated. This

compile the Measurement System section of this roadmap and many

process is illustrated in Fig. 4.

NMIJ researchers are involved in. This roadmap lists all technologies

The second calibration service is for the line width of a photo maskneeded for future and shows the directions of technology development

drawn on a glass substrate with chromium. The calibration is done byin order to promote the collaboration of different sectors, such as

using a SEM, but as explained before, the measurement results byindustrial, academic and public sectors. This roadmap is updated

SEM has a systematic bias in the edge detection. The bias is

every year. Any inputs which will be included in the next version arecompensated by comparing the measurement results of the traceablewelcome.

AFM. Nevertheless the AFM also has a systematic bias; therefore its
probe shape is characterized by measuring a sharp needle. To resolve
this bias compensation for different measuring methods, thetraceability chart for the line width calibration became complicated asshown in Fig. 5.

Fig. 3 Nano scales and calibration services which underpin thedevelopment of semiconductors. The red line indicates theminimum manufacturing size expected in the International
Technology Roadmap for Semiconductors (ITRS).

Fig. 4 Fabrication of ultrafine 1-D grating

- Some members are impatient as they are thinking ‘First come,first served.’- Some members are not accustomed with standardization well.
- As the TC is new, it is still in chaos and rules are not fixed yet.
I believe the most important thing to avoid this confusion is having
discussions based on technical background, tangible evidence and thescientificconsideration

ofmetrology

andtraceability.

Only

metrologists and National Metrology Institutes can settle thiscontroversial situation and play important roles to underpin thedevelopment of nano technology.
References
1) The laser frequency listed in MeP can be found in the interactive
Fig. 5 Traceability chart of line width (photomask)

web page of BIPM (Bureau of International Weights andMeasures) site.

7. Necessity of industrial standard

http://www.bipm.org/en/publications/mep.html

As explained many times, in nano metrology, measurement results
are method dependent and therefore most nano technology users are
in inconvenient situation.
many industrial fields. Let us imagine conventional precisionengineering. It has been primarily used in machining industry. On thecontrary, nano technology is used not only in semiconductor industry
but in many others such as chemical, medical, food, cosmetics, andindustries.

Itmeans‘interchangeability’and‘interoperability’ are important. If the measurement procedures andconditions are commonly agreed and documented; i.e. industrial
standards are established, interchangeability and interoperability will
effectively work.
While the original purposes of making industrial standards are toimprove interchangeability of industrial products and promote
development of industries, industrial standards have been utilized as a
strategic tool of international competition. Since nano metrology is a
newly emerging filed, this strategy is emphasized more andinternational competitions are more intense.
ISO/TC 229 introduced above is a newly established technicalcommittee in May 2005. Since then two meetings are held every year.
One technical report (TR) and one technical specification (TS) havebeen published and 6 TR, 22 TS and 6 international standards (IS) arebeing discussed in TC 229.
I have been involved in standardization activities for many years
and understand the importance of industrial standards including TC
229. However, I found a notable sentence in the minute of TC 229
held recently that ‘the importance of the committee’s strategic plan
regarding the needs of the users were emphasized, as it appeared thatsome NWIPs were opportunistic and not aligned with the strategicplan (from ISO/TC 229 N 658, Draft report of the 9th meeting).’
Concerning this expression I don’t know whether the strategic planor the experts participating in the TC is bad. I, however, am afraid thatthe importance of industrial standards is emphasized too much so that
too rapid and rough discussions and proposals have been made in theTC.
Possible factors for this is- Some members are misunderstanding the objective of industrial
standards,

lasers as standards of wavelength: the helium–neon laser at 633
nm”, Metrologia, Vol. 46, No. 1, p.11 (2009).

One of the peculiarities of nano technology is that it is used inenvironmental

2) J. Stone, et. al., “Advice from the CCL on the use of unstabilized3) Edited by Ministry of Economy, Trade and Industry, Strategic
Technology Roadmap 2010.
http://www.meti.go.jp/policy/economy/gijutsu_kakushin/kenkyu_kaihatu/str2010.html (in Japanese)
4) I. Misumi, et. al., “Application of a GaAs/InGaP superlattice innanometric lateral scales,” Measurement Science and Technology,
Vol. 18, No. 9, p.2743 (2007).