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NBS SPECIAL PUBLICATION 611

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

New Technology

Challenges Metrology
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities2 — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Mechanical

Engineering and Process Technology2 — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

2 Some divisions within the center are located at Boulder, CO 80303.
MAT1UMAL BURCA1

OF RANBUM

New Technology Challenges Metrology AUG 2 0 1981

Judson C. French, Director

Center for Electronics and Electrical Engineering

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Presented at the Interamerican Metrology Conference,

Marking the Formal Establishment of the Interamerican

Metrology System, Held in Buenos Aires, Argentina,

September 4-7, 1979

Conference sponsored by: The Argentine National Institute of Industrial Technology Buenos Aires, Argentina

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued July 1981
Library of Congress Catalog Card Number: 81-600063

National Bureau of Standards Special Publication 611

Nat. Bur. Stand. (U.S.), Spec. Publ. 61 1, 90 pages (July 1981

)

CODEN: XNBSAV

For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington, D.C. 20402

Price $4.50

(Add 25 percent for other than U.S. mailing)
NEW TECHNOLOGY CHALLENGES METROLOGY

Judson C. French

Abstract

Assurance of measurement quality to meet requirements for

regulatory agencies, marketplace equity, and productivity

and quality control in manufacturing and research is

challenged by unprecedented demands for sensitivity, speed,

precision, and accuracy over wide ranges of properties and

signal characteristics. New approaches are needed.

Examples of NBS response, principally in electrical and

electronic engineering, are described.

Key words: Calibration; electrical; electronics; engineering; hazards; measurement; metrology; National Bureau of

Standards; power; radiation; semiconductor; technology

1 . INTRODUCTION

A new era is in the making in requirements for metrological services.

In broad areas of scientific, industrial, and governmental measurement

activities, the traditional metrological services, such as hierarchical

calibration laboratory systems that have assured adequacy of precision and

accuracy in practical measurements in the past, are no longer sufficient.

There are several reasons for this change.

Practical measurements now require unprecedented sensitivity,

precision, and accuracy, over an extremely wide range of material or system

properties and signal characteristics. This is true in the research

laboratory, on the production line, in the field operations of the military

services, or in measurements in support of governmental regulatory efforts

concerned with air or water pollution or electromagnetic radiation intensity.

The requirements of these practical measurements may be close to or exceed the state of the measurement art, and yet reproducibility of the

measurements between various concerned parties, and accuracy based on accepted

national or international standards, are important for the legal requirements

of regulatory agencies, for equity in the marketplace, for reliability of the

performance of critical products or systems, and for enhanced productivity in

the manufacturing and process industries.

In many cases, these measurements must be made at very high speed,

either because of the transient nature of the signal itself or because of the

necessity for making a large number of repetitive measurements in reasonable
times. Often it is impractical for measurements to be made effectively by

hand; automation of the process becomes essential where the required speed and

quantity of measurements exceed human capabilities, or where the measurement

must be performed in places unsafe for, or inaccessible to, a human operator.

In particular, the pervasive application of electrical and electronic

systems for control and communication and for energy generation and

transmission has both broadened the availability of new measurement methods

and extended to new extremes the range of electrical signals and properties to

be measured and controlled. The burgeoning field of solid-state electron

devices has produced new tools such as the microprocessor to aid in automation

of measurement. But it has simultaneously placed new demands on the

measurement art for sensitivity and speed in measurements through its routine

needs for part-per-billion sensitivity in measurements of the properties of

solid-state materials used in the manufacture of these devices, and for speed

in measurement of the properties of devices intended for use in information

systems operating in the gigabit-per-second range.

Thus, to respond to these new levels of sophistication and complexity, new services are needed from our national measurement laboratories and

throughout the measurement chain extending from national laboratories to the

place of practical measurement application.

To illustrate how the National Bureau of Standards is responding to

this challenge, I will describe in some detail several examples of the new

requirements, some new approaches to metrological services, and some responsive activities undertaken at the National Bureau of Standards. In

particular, I will emphasize NBS activities in electrical and electronic

measurements

.

2. NBS RESPONSE TO METROLOGICAL CHALLENGES

Let me address first the National Bureau of Standards (NBS), and some of its responses to this metrological challenge. NBS, with its principal

facilities in Gaithersburg, Maryland (figure 1), and in Boulder, Colorado

(figure 2), is well known for its traditional activities in maintaining the

fundamental standards of measurement for the United States of America; for its

activities in disseminating these standards through a hierarchical,

cooperative system to governmental and commercial calibration laboratories

throughout the country; and for its activities in cooperation with other

countries to maintain compatibility of measurements on an international

scale. However, the scope of NBS research and services is far broader than is

commonly recognized. NBS comprises three principal technical elements (figure

3), the National Engineering Laboratory (NEL) , the National Measurement

Laboratory (NML), and the Institute for Computer Science and Technology

(ICST). At NBS, work is done on a surprising variety of subjects: in NML

(figure 4), on the basic measurements of mass, length, time, and so forth, of

course, but also on nuclear physics, analyticial chemistry and fundamental

material properties, even air and water pollution and dental materials; in NEL

(figure 5), on electronics, automation in the mechanical manufacturing

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industries, building technology, fire research, and safety of consumer

products; and, in ICST (figure 6), on computer standards; to name only a few. All this work is required to help provide the measurement methods, data,

theory, and associated technology that the scientific community needs for its

research; that the manufacturing industries, their suppliers and their

customers, including the Government, need either for manufacturing control or

for the specifications underlying procurement; and, finally, that governments

need for fair and reasonable regulation.

It is a matter of concern to each individual research center in NBS to

provide efficient and effective means to deliver needed measurement-related

services in its specific field to its customers. It is a matter of concern to

NBS management to seek new Bureau-wide means to assure effective services.

For example, a central Office of Measurement Services (figure 7) has been

established which makes known publicly the measurement services NBS provides,

such as its traditional calibration services. This office also plays an important role in developing new measurement dissemination methods such as Measurement Assurance Programs. These Measurement Assurance Programs, or MAPs

as they are called because of their acronym, supplement the hierarchical

calibration system and provide greater assurance that a measurement is

performed with known precision or accuracy. MAPs depend on a particular

application of calibrated measurement instruments or artifact standards by the

several participating laboratories. Each laboratory retains an artifact which

it measures periodically to establish the laboratory's internal precision from

charts of its data over time. These measurement results include the effects

of errors due to the laboratory's measuring instrument, the operator, the

environment, and so on. Periodically an artifact, carefully calibrated by the

central laboratory, such as NBS, is circulated among the participating

laboratories for measurement. After appropriate treatment of the data from

all laboratories by the central laboratory, each laboratory is then able to

compare its own mean and standard deviation against those of the central and

other participating laboratories, with its own performance maintained

private. It is then able to take steps to improve its capabilities if

necessary. The most important factor in a MAP program is the evaluation of

the complete measurement process as it is actually performed in the

laboratory; this evaluation is not available from the usual practice of

submission of a standard to the central laboratory for calibration.

Incidentally, the central laboratory may also benefit from the MAP through

reduced requirements for routine calibrations.

The NBS Office of Measurement Services also conducts studies of new measurement requirements likely to affect the entire Bureau. A recent example

is a study of the effect the introduction of the microprocessor will have on,

first, the way the Bureau conducts its internal measurement research and,

second, the new measurement services that NBS must provide because the

microprocessor is expected to change dramatically the way practical

measurements are made in science and industry.

Another central office is devoted to standard reference materials

(figure 8): to the coordination of the work carried on throughout the Bureau

which leads to their development, their production, and their sale. These

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carefully analyzed materials are made available, along with instructions for

their use, as a means of checking the quality of an analytical or other type

of measurement at the actual site of performance. Over 1000 different

standard reference materials are provided by NBS (figure 9). These cover an amazing range of materials, from spinach, tomato leaves, and pine needles

certified for content of over a dozen trace elements such as manganese and

lead so that environmental and agricultural scientists can calibrate analytic

tools and measurement methods, to highly purified gallium (99.99999% pure)

used to provide a temperature reference point (known to 0.0007°C) for control

of diagnostic tests in clinical chemistry. Each of these SRMs is of great

significance to some industry, research laboratory, or regulating agency.

The metrology-related research at NBS is broad and is increasing in its

breadth to meet new requirements. Simultaneously, the services to make its

research results available to an ultimate user in the most effective way are

of necessity broadening. I have only touched superficially on a few examples

of such efforts so far. The subject is far too complex to describe in depth

here. So let me pick as an example samples of the work of the Center for

Electronics and Electrical Engineering, to give you an impression of the way

just one NBS Center is responding to the new challenge in metrology.

= 4 =
3. THE CENTER FOR ELECTRONICS AND ELECTRICAL ENGINEERING

The Center for Electronics and Electrical Engineering provides a focus

(figure 10) in NBS for addressing electrical, electronic, and electromagnetic

materials, components, instruments, and systems. It provides (figure 11)

well-documented and evaluated measurement methods, data, and interpretive

theory; physical standards, traceability to these standards or measurement

assurance programs; and associated technology and technical services. It

provides these to government, industry, and the scientific community,

ultimately benefiting the consuming public. These services are essential to

equity in domestic and international trade, to control of manufacturing

processes, and to the applications of a number of other Federal agencies.

The work of the Center has five principal programmatic thrusts (figure

12), each addressing closely-related technologies, a corresponding market, and

technical and societal problems of current significance. These thrusts are

in (1) Semiconductor Technology, (2) Fast Signal Acquisition and Processing,

(3) Fast Signal Transmission, (4) Electrical Systems, and (5) Electomagnetic

Sensing and Hazards. I will treat each of these in turn by describing factors

stimulating our work and our responses in measurement research and delivery.

3.1 Semiconductor Technology

Challenge

Semiconductor devices and integrated circuits lie at the heart of the

modern electronics revolution (figure 13). Semiconductor technology is

therefore central not only to electronics but to the economic and social

health of modern industrial societies.

The semiconductor device industry provides extreme challenges for the

metrologist. It deals with the purest and most perfect materials known to man

and with microscopic and submicroscopic dimensions. It is concerned with

trace impurities at concentration levels ranging from parts per trillion to

parts per million, with controlled variations in these concentrations which

range over several orders of magnitude over a span of less than a micrometer;

with dimensional integrity of tenths to hundredths of a micrometer; with

circuit element densities of hundreds of thousands of devices per square

centimeter; with signals in the gigahertz range; with currents in the

picoampere range and less; and with a host of new processing technologies

which involve the interaction of radiation with matter, plasma physics,

photopolymer chemistry, etc. Despite the great success of this industry in

providing new and sophisticated products, it has outstripped available

metrology. New and refined techniques are essential for use both in

manufacturing control and in the marketplace. In the United States of

America, both Federal agencies and industry have called on the National Bureau

of Standards to aid in developing this needed measurement technology.

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NBS Response

In response, NBS is conducting a broad program in semiconductor

measurement technology (figure 14). This program includes research and

development on measurement technologies related to mechanical, electrical, and

crystallographic properties of finished devices. The program also seeks to

develop more effective ways to disseminate this measurement technology. Let

me illustrate both this program and the new ways by which NBS must address

traditional metrological areas by examples which relate to measurements of

length and material properties.

Semiconductor devices are fabricated by changing the concentration of

selected impurities in defined regions in a very pure and perfect crystal,

usually silicon (figure 15). A photolithographic process is used to define

the regions which comprise a device. One of the critical problems in

semiconductor device design and manufacturing is the control of dimensions of

these regions. Microscopic measurements of features on patterned photomasks

and silicon wafers require interpretation of the optical image of a line or

a space between lines. The threshold (figure 16) which corresponds to the

actual material edge depends on the particular optical system employed in the

measurement. For pitch measurements (figure 17), errors in threshold cancel

so that accurate measurements on features between edges of the same type

(e.g., left-hand or right-hand edges) can be made without accurate knowledge

of the threshold. For width measurements, however, errors due to improper

selection of threshold add rather than cancel. Until recently, such errors and the resulting inconsistencies between different types of instruments and

between laboratories were insignificant. This is no longer so. Apparent

differences of 0.25 micrometer or more were observed when measuring lines or spaces with optical instruments using different means for identifying edges

such as filar or image-shearing eyepieces. Concern with such errors increased

substantially both when process control became more demanding and when it

became apparent that feature sizes for future integrated circuits would reach

the micrometer and submicrometer range (figure 18). To solve this problem NBS

researchers in several cooperating centers extended the existing theory of the

optical microscope and developed an automated scanning photometric microscope

(figure 19) with a novel laser-controlled stage to make the measurements.

With the understanding and techniques developed in this research it was possible to calculate accurate image profiles (figure 20) and threshold levels

and to make linewidth measurements accurate to about 50 nm on lines as narrow

as 0.5 micrometer. In addition, procedures were worked out to permit accurate

measurements of linewidths with the use of suitable instruments available in

the field. These techniques are being transferred directly to the industry

through the use of workshops (figure 21), which include the opportunity for

hands-on measurement of linewidths with the use of a variety of commercially

available instruments provided to the workshops through the courtesy of the

instrument manufacturers and through a series of new standard reference

materials. The first of these, SRM 474 (figure 22), designed for use in

measuring opaque photomasks in transmitted illumination, is expected to be

available before the end of this year. This standard reference material

contains a pattern of lines and spaces in the 0.5- to 10-micrometer range

together with other patterns which permit line spacing calibrations and

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setting of edge-detection thresholds on automatic measuring instruments.

Together with the associated measurement procedures (figure 23), this artifact

provides the user with the capability of evaluating his own measurement

procedure and calibrating his instrument. Artifacts with similar patterns in

various layers on silicon wafers and in semitransparent photomasks are planned

for the future.

Manufacture of semiconductor devices involves repetitive patterning of

the semiconductor wafer by means of photographic processes. Registration of

the various layers to submicrometer tolerances is critical. Misregistration

can occur because of design errors, photomask fabrication errors, or distortions in the photomasks or in the silicon wafer itself. A

microelectronic test structure has been developed which can be used to

determine registration errors between selected mask levels (figure 24). The

test structure is fabricated on a silicon wafer using manufacturing processes

similar to those used for making integrated circuits. The structure is

repeated at intervals across an entire wafer. Electrical measurements made

with an automatic wafer prober (figure 25) can be used to detect translational, rotational, and distortion errors with a resolution of about 0.1

micrometer. Computer- generated wafer maps of misregistration as a function of

position present the information graphically (figure 26). The test structure

can be utilized in evaluating photomask generation equipment, photomask

aligners and printers, mask aligner operators, and wafer distortion. The

range and resolution of the structure itself were determined by means of

correlations with specially designed wedge-shaped optical scales which could

be measured in a conventional microscope.

Microelectronic test structures (figure 27) have also proven to be very

useful in measuring electrical material characteristics. Several years ago a series of test patterns was developed to facilitate determinaton of the

relationships between resistivity and dopant intensity, two critically

signifcant material parameters in silicon. These patterns (figure 28) contain

specially designed microelectronic test structures including a planar square

four-probe array for measuring bulk resistivity, a circular junction diode

with external field plate for measuring dopant- impurity density, along with

other ancillary structures. These patterns also proved to be useful in

setting up semiconductor fabrication lines, especially for organizations not

previously experienced in this field. More than 60 different organizations in

industry, Government, and academia have acquired the mask sets for these

patterns. The dopant impurity density distribution controls the electrical

activity of a semiconductor device structure. Dopant densities may vary over several orders of magnitude in a region a few micrometers on a side and a micrometer or less deep (figure 29). Numerous complex methods have been

developed to measure this variation. A new measurement technique based on the

use of a metal-oxide-semiconductor field-effect transisitor (MOSFET) is being

investigated (figure 30). This method permits profiles of dopant densities to

be measured on a high-speed wafer prober by d-c techniques, and avoids the

necessity for preparing special samples, nonstandard surface preparation such

as polishing or beveling, insertion of the specimen into a high-vacuum chamber

with the use of Auger electron spectroscopy or secondary ion mass spectroscopy, or the use of high-frequency test signals as with capacitance

voltage measurements.

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A new class of test structures which contain integral electronic

circuity to provide signal processing at the point of measurement is being

developed for the measurement of very elusive quantities, such as picoamperelevel leakage currents. Use of a gated-diode MOSFET structure (figure 31)

combined with a throw-away electrometer built into the wafer enables one to

measure, by d-c techniques in a short period of time, properties related to

defects or impurities in the crystal which control the leakage currents,

response time, or storage time of circuits. Use of these integrated test

structures makes it possible to map over the surface of a silicon wafer

(figure 32) properties such as charge carrier lifetime which can be correlated

with crystal defect or impurity densities.

3.2 Fast Signal Acquisition and Processing

Challenge

The development of high-speed signal processing laid the basis for the

modern computer and for the information and control revolution that is

predicted to be of at least as great significnce to society as the industrial

revolution in the nineteenth century (figure 33). The impact of computers,

and more recently of microprocessors, in science, in automation of

manufacturing and process control, in business and banking, in medicine, in

communication, and in defense is too well known to require delineation here.

The advent of digital signal-processing techniques has simultaneously

ushered in an important new era for the metrology community. Whereas

classical analog standards such as standard (Weston) cells, or Kelvin-Varley

dividers, potentiometers, and the like have served well as the basis for

calibrating electrical measurement instruments and test equipment, modern

electronic instrumentation utilizes fast signal-sampling techniques for which

there are few analogous physical standards, adequate characterization methods,

and rigorous calibration procedures. The metrology support for important

modern instruments and equipment such as digital voltmeters, phase meters,

multimeters, oscilloscopes, spectrum analyzers, etc., still often relies on

the manual calibration of a few selected parameters and test points based on

static laboratory standards. Automation is required (figure 34).

Further, the newest test instruments themselves now have digital signal

processing capabilities "built-in" by means of microprocessors and other

related data-processing devices. Consequently, the validity of the

measurements made by these instruments is dependent on the software algorithms

and the integrity of the digital logic, as well as on the data-acquisition

hardware. This dependency particularly applies to the evaluation of the

performance of complex systems such as automatic test equipment. At present,

neither military nor industrial procurement tests of complex automatic test

equipment are satisfactory from the point of view of performance assurance.

Nevertheless, there are both national and international requirements

for achieving agreement on the performance accuracies of test, measurement,

and diagnostic equipments. In the United States of America, for example,

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there are military contractual agreements with suppliers which require that

measuring and test equipment be calibrated using instruments or artifact

standards whose calibration in turn is certified as being traceable to

national standards at NBS. Similarly, Federal regulatory agencies (such as the Environmental Protection Agency, the Nuclear Regulatory Commission, the

Consumer Product Safety Commission, and the Food and Drug Administration)

invoke traceability to NBS standards in their regulations and handbooks.

Consequently, a challenge exists in providing the means by which these

traceability requirements can be achieved. New physical reference standards

which provide for increased ranges for the parameter in question, new test

parameters (such as audio-frequency phase angle), dynamic stimulus or measurement capabilities, and the ability to be programmed automatically are required for this purpose. Because in many cases a large number of data points

is desired for statistical reasons and because time is often an important

factor, automated test and calibration facilities applying these new reference

standards must also be developed.

Emerging electronic technologies greatly tax present methods for

measuring fast transient phenomena. These new technologies are evolving

ultra-fast signal-processing equipment which has been called gigabit

electronics. Systems which currently process signals in a strictly analog

fashion will become primarily digital in design, and there will be a commensurate revolution in system performance because of the flexibility of

digital processing. Whereas narrow-band measurements were satisfactory in the

past for characterizing microwave systems, the future emphasis will be on broadband measurements which involve devices such as analog-to-digital

converters, samplers, and signal-level discriminators. Signal frequencies

will extend into the optical region, with the aid of new optoelectronic

devices and circuits and transmission in optical fibers.

Two important new technologies, potential contributors to gigabit

systems, are based on gallium arsenide and superconductivity. Gallium

arsenide devices are already in wide use. Superconductivity is being applied

to experimental computer technology, and the published speeds of operation are impressive (e.g., 13 ps for an "OR" gate operation). These performance levels

are beyond current test instrumentation performance. Since the new technology

has already moved beyond present test instrumentation capabilities, it is

essential that accurate new measurement methods be developed.

Improved methods for dissemination of standards must also be developed

in order to provide a more direct traceability link to these new laboratory

standards. For complex automatic test equipment, for example, it is not enough

to ensure that the built-in secondary reference standards are accurately

calibrated at regular intervals. If the adequacy of the software and the

interface hardware is not completely verified, the system may be producing

inaccurate measurements of the unit being tested. A more direct approach is

being considered at NBS for which dynamic transport standards would be

developed which are traceable to NBS and can be used in automatic test system

calibration verification on site. A system is visualized in which NBS

verifies the performance of the highest accuracy transport standards for a

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relatively small number of key standards laboratories in industry and

Government. These organizations would then utilize the high-accuracy

transport standards through a minimum of intermediate steps (perhaps employing

commercially available standards), to verify automatic test equipment in the

field, with the transport standard playing the role of the unit being tested.

NBS Response

The present response at NBS (figure 35) to the support of high-accuracy

electronic instrumentation and equipment has as major thrusts the development

of new or improved physical reference standards, associated test methods, and

calibration techniques; extension of the range of services; and new

dissemination means such as transport standards. In many cases the new standards must embody the very technologies which call for their development!

For example, NBS has developed two precision linear digital-to-analog

converters to serve as reference standards for completely characterizing the

static and dynamic performance of high-accuracy digital-to-analog and analogto-digital converters such as those used in automatic test equipment

systems. One is an 18-bit digital-to-analog converter (figure 36) which has a relatively high current output capability and can, therefore, be used to drive

remotely located loads without degrading its output performance. This unit

can make 20,000+ conversions per second, has less than one-half leastsignificant-bit root-mean-square noise, and is intended to be used for testing

dynamic performance parameters, such as the settling time of commercially

available precision converters.

The second converter standard is a 20-bit unit (figure 37) which

consists of a very accurate programmable voltage source having full-scale

ranges of ±2.5, +5, and +10 V, and less than 1 ppm linearity error relative

to the full-scale range.

A test method using this 20-bit instrument has been developed which can accurately measure the output levels of digital-to-analog converters as well

as the input transition levels in the transfer characteristics of analog-todigital converters. A test facility using these techniques (figure 38) is

being developed which can scan all possible code states to provide calibration

data with 1-ppm resolution on offset, gain, differential and integral

linearity errors, and equivalent converter input noise, as well as on monotonicity and missing codes in data converters. A calibration service for

data converters using this test facility is planned.

A test method has also been devised for accurately measuring dynamic

gain error, signal delay, acquisition time, sample/hold offset, aperture time

delay, and related parameters in sample-and-hold amplifiers. A prototype

transformer-ratio-arm bridge circuit is being developed which presently can make amplitude measurements on ac signals up to 50 kHz with bridge errors to

within 50 ppm and can make time measurements with errors of 4 ns. Extension

of this work to provide these measurements on higher frequency signals is

planned.

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Precision waveform sources using digital synthesis techniques are being developed to serve as standards for calibrating the dynamic performance

of instruments and equipment. One source is a programmable audio-frequency

phase-angle standard (figure 39). This instrument will provide a pair of

precision sinewave output signals whose relative phase difference is accurate

to +0.005° from 20 Hz to 5 kHz. A new calibration service for commercial

phase-angle meters is to be provided using this standard. The frequency range

coverage will be extended.

An example of precision digital signal acquisition and processing is an ac voltmeter (figure 40) which can take samples from low-frequency ac waveforms over a range of 0.1 to 120 Hz and determine the rms value, period

or fundamental frequency, and total harmonic distortion in a time of only

two periods of the input signal to an accuracy of 0.1%, or better.

At the other extreme, in support of high-speed time-domain measurements

and related instrumentation, NBS is developing systems for the measurement of

waveforms of optical and electrical signals that are consistent with one another, are referred to a common set of basic standards, and are capable of a time resolution of 10 ps.

The NBS Automatic Pulse Measurement System (figure 41) is a digital

computer-controlled system that acquires time-dependent data from electrical

or optical pulses or signals, and processes the acquired waveforms in order to

estimate pulse shape or pulse response, signal correlation functions, and

complex spectra.

Typical time-domain standards associated with this system include

transition duration transfer standards, impulse generators (figure 42), and a time-domain antenna range (figure 43) for the production of standard pulsed

electromagnetic fields.

Further, in support of the measurement technology and standards

required by the emerging gigabit electronics, NBS is studying the technology

of superconductivity and the potential 1-ps switching time of Josephson

junctions (figure 44). The objective is to press toward the limits in speed

and accuracy of electronic measurements which may best be achieved by

superconductor techniques. Circuitry similar to the lower-speed signal

sources, converters, and sampling units mentioned earlier will be required.

Work on these is underway. For example, a 4-bit analog-to-digital converter

(figure 45) based on Josephson junctions and employing 5-micrometer linewidth

lithography has been developed. It operates in the range of hundreds of

megasamples per second.

Practical superconductor measurement instruments will require practical

refrigeration systems to avoid the use of liquid helium or bulky and

electrically noisy refrigerators. A Stirling refrigerator (figure 46) has

been developed which can reach liquid helium temperatures.

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It will be a long time before the superconductor work produces a calibration service! In the meantime, the technolgy developed is promptly

made available to other research and development organizations through a variety of means.

3.3 Fast Signal Transmission

Challenge

The emergence of fast signal electronics (figure 47) and of other

technological advances, such as satellite systems, lasers, and optical fibers,

is having a dramatic impact on signal transmission for telecommunications,

navigation, and remote sensing.

Telecommunications is in a period of rapid expansion as markets develop

in geographically remote parts of the world and in the business sector of

industrialized nations. The technologies of satellite microwave signal

transmission, optical fiber signal transmission, and of computers are driving

forces. Satellite communication systems, which can employ small low-cost

earth terminals, are ideally suited to serve remote locations. The

proliferation of computers in all aspects of business is creating a large

volume of traffic in digital data. Satellite and optical fiber systems offer

broad bandwidth for communication and are well adapted to the growing trend

away from direct AM or FM transmission of audio or video signals and towards

digitized signals using pulse-code modulation and time-division

multiplexing. They are thus excellently suited for business communications.

Both satellite and optical fiber transmission technologies depend for

their commercial success on pressing the practical limits of detecting weak

signals and of discriminating against noise and interference. Hence they are both very measurement sensitive. The metrology demanded in support of these

developments must cover an increasingly wide dynamic range and spectrum of

frequencies. Also, it must provide for characterization of components and

signals with fine resolution in the time domain.

Developing navigation and remote-sensing applications include

collision-avoidance systems and microwave landing systems for aircraft,

satellite-based navigation systems, and new radar and laser sensing systems.

The advent of the small computer has made a dramatic improvement in the

information that can be obtained from radar reflections. This has led to very

complex systems using large, phased-array antennas. There are many advantages

for these systems in using shorter wavelengths than hitherto, and after many

years of unfulfilled promises serious development work is in progress at

frequencies up to 300 GHz. Because of the existence of dense absorption bands

in the atmosphere, the natural extension of this trend will be a leap to the

other side of the bands in the infrared, where there are powerful laser sources at wavelengths of 10 micrometers and shorter. These are used in many

military systems under development for surveillance, the guidance of weapons,

and even as destructive weapons.

- 12-
These advances lead to requirements for an extension of measurement

capabilities to cover higher microwave and millimeter wave frequencies, and

very high laser power and energy at 10-micrometer and shorter wavelengths.

Less obvious but extremely demanding is the need for low-energy

measurements. Equipment to evaluate laser guidance systems must be capable of

measuring radiation at a level of 10~ 16

J. At 1.06 micrometer, this

corresponds to only 500 photons in a pulse.

NBS Response

To support development and trade in signal-transmission technology, NBS

is responding (figure 48) in areas which include microwave and millimeter wave components, antennas, satellite ground stations, optical fibers, and lasers.

NBS has provided RF and microwave measurement services for many years. The

character of these services is now changing dramatically in response to the

changing demands of the technology and the markets they support.

Ten years ago, microwave calibrations were performed on accurately made

and carefully tuned manual systems (figure 49). Accurate workmanship and

patient tuning were at a premium. This mode of measurement became obsolete as microwave measurements covering a wide spectrum of frequency were required to

support broadband systems, and the time taken for retuning at each change of

frequency became an intolerable disadvantage.

New measurement systems, known as automatic network analyzers (figure

50 ) , have substituted complexity of computation for accuracy of workmanship

and operator skill. They operate under the control of a computer and

calibrate themselves with the aid of simple check standards at each frequency

at which measurements are to be made. Raw measurement data are stored in the

computer, which then applies the appropriate corrections to the measurements

automatically. The accuracy of each individual measurement is not

significantly changed from the manual measurement, but the great speed and

efficiency of the new technique provide a great economy in measurement, and

enable a much more thorough characterization to be made of the device

measured.

An excellent example of the new style of measurement system is the 6-

port, which was invented at NBS several years ago and is now in an advanced

stage of development. It is based on the general properties of waveguide

junctions with six ports (figure 51). Typically, one of the six ports is

connected to a signal generator, another defines the plane at which

measurements are to be made, and the other four are connected to simple

amplitude detectors, such as diodes or bolometers. No phase measurements are

made. General microwave scattering theory leads to a set of simultaneous

equations that relate the complex description of the wave at the measuring

port to the amplitudes observed at the four amplitude-measuring ports.

Probably the most generally useful 6-port system employs two 6-port

junctions powered by a common signal source to form an automatic network

analyzer (figure 52). The combined calibration routine for the two 6-ports

can be particularly elegant, and requires no calibrated standards if

-13-
measurements of dimensionless ratios (such as attenuation and phase shift) are

to be made. Measurement of quantities (such as power and impedance) that have

dimensions require a single standard of each. When calibrated, the dual 6-

port can measure all the characteristics of any 2-port device, active or passive

The complete dual 6-port system (figure 53) is quite compact, because

its operating principle does not require frequency conversion to measure

phase, as other automatic microwave measurement systems do. A programmable

desk calculator is used to control the measurement process and to compute the

results. This system now operates in the range from 2 to 18 GHz. Its

accuracy and stability have been evaluated. For attenuation measurements, for

example, systematic error varies from 0.001 dB at 15 dB to 0.15 dB at 60 dB.

The dual 6-port needs recalibration only at intervals of several months to

maintain this accuracy.

Because it does not rely for its accuracy on the calculable properties

of its components, the 6-port principle will be a powerful tool for extending

the range of microwave measurements into the millimeter wave part of the

spectrum. A 6-port system operating at 95 GHz is already under construction

at NBS.

Control of errors made in microwave measurements in the field can be

improved by better dissemination of reference standards. To accomplish this,

a new measurement assurance program is planned.

In addition to the measurement on microwave circuit components, NBS

provides a measurement service for complex antennas (figure 54). In one of

the techniques, the near field (figure 55) of the antenna is scanned

systematically to measure phase and amplitude over the whole beam. From this

information, the far-field radiation pattern (figure 56) is reconstructed

automatically by a computer. The accuracy is as great as any that can be

obtained on a farfield antenna range, while freedom from environmental effects

and from the use of extensive outside ranges offers many advantages.

Another measurement system developed at NBS evaluates the performance

of satellite communication ground stations (figure 57), using a radio star for

reference

Optical fiber (figure 58) communication systems will ultimately require

measurement services and standards comparable to those presently provided for

microwaves. Measurement systems for attenuation, power, and bandwidth are under development (figure 59).

The work at NBS on laser measurements is based on standards of power

and energy such as calorimeters (figure 60). They are used to provide

measurement services that are heavily used by manufacturers of laser systems,

who have to prove their compliance with laser safety regulations.

The range of laser power and energy measurements is wide. At one end,

a laser and electro-optic pulse shaper are used to evaluate detectors at 10.6-

micrometer wavelength and high power densities. The laser generates pulses of

- 14-
nanosecond duration and peak power densities of 25 MW/cm . At the other end

of the scale, a system to measure laser energy at the 10 J level has

already been developed and evaluated.

3.4 Electrical Systems

Measurements at low frequency and very high voltage and power are important to researchers in high-energy atomic and molecular phenomena,

manufacturers and users of medical x-ray equipment, and in the defense

industry, but clearly the primary application is in the electrical power

industry.

The world's energy crisis has drawn attention to all energy-producing

and distributing activities, including those that relate to the distribution

of electrical energy (figure 61). As petroleum-based resources become

depleted, the emphasis will have to be on greater utilization of other

resources such as coal and nuclear energy. Electricity is often the only form

for end use. Thus the growth of electric energy consumption is expected to

continue at nearly the historic rate, doubling in the United States of America

in ten to fifteen years in spite of reduced growth in total energy

consumption.

New technology is needed to transmit electrical energy in an acceptable

manner. Specifically, the power energy density of available rights-of-way

must be increased. One way to achieve this increase is to transmit power at

higher voltages.

Overhead transmission at extra high voltage levels (EHV) , from 345 kV

to 765 kV, has already been introduced. Experimental transmission lines are being tested at ultra high voltages (UHV), above 1 MV. There are objections

to overhead lines on environmental grounds. They are considered to be

unsightly, and there are concerns about potentially adverse biological effects

resulting from high electric fields under such lines.

Underground transmission overcomes environmental objections, but is

perhaps 10 to 20 times more costly to install and operate. Underground lines

also have higher losses and are to date less reliable. Hence, underground

lines are presently used for very short distances only in locations where

overhead lines would be unacceptable, e.g., in densely populated urban areas.

There are great challenges to develop less costly, higher capacity, and

more reliable underground transmission systems. Alternatives being explored

are SF^-insulated lines, cryogenic lines, and lines with synthetic liquid and

solid insulators. In each case, new material property data and test methods

for line performance are required.

Advances in electronic and computer technologies are affecting the

control and monitoring of the electrical power systems and the consequent need

for new metrology. In high-capacity power systems, decisions about faults and

their clearances must be accomplished within a fraction of a cycle. Elec-

-15-
trical quantities in power networks must be sensed and measured with

increasing accuracy. Efforts are being made to reduce generating peaks and to

implement rate structures which will take into consideration varying costs of

supplying electricity during a day or season; load management and variablerate metering are emerging; new instrumentation will call for new calibration

and measurement services.

NBS Response

In the past, NBS has been responsible for providing primary standards

upon which electrical energy metering in the United States of America is

based, ranging from watthour meters for individual users to instrument

transformers used in intersystem metering, and encompassing numerous other

related measurement services for power systems (for example, for high-voltage

and power-factor correction capacitors, and dividers to measure high AC, DC,

and transient voltages) with the emphasis on measurements under very

controlled laboratory conditions.

The trends in electrical power transmission technology are placing new

demands on NBS services (figure 62). The necessity is arising to provide

higher voltage measurements on the user's site. New measurements are required

for environmental investigations. New measurements are required to aid the

industry to develop new underground transmission technology. And improvements

in accuracy are required to support advances in modern instrumentation and

data processing.

Extensions of voltage ranges and calibrations in the field are necessary in connection with voltage measurements, both steady state and

transient, in the EHV and UHV ranges. Power-line voltages in these ranges are measured by first reducing them by means of a capacitative voltage transformer

(figure 63) as opposed to the more conventional inductive divider used at

lower voltages. Capacitive transformers do not have the intrinsic stability

of their inductive counterparts. Hence periodic rechecks after initial

installation are desirable, and are becoming even more important as metering

errors become more costly. It is impractical to dismantle capacitive

transformers and bring them back to the laboratory for calibration. NBS, in

collaboration with the Electric Power Research Institute, has developed a transportable system for on-site calibrations (figure 64).

Similarly, since the ratio of an impulse divider is very much affected

by the laboratory environment due to stray capacitances, unique grounding

systems, and electromagnetic coupling with other equipment, NBS performs

impulse calibrations in the customers' laboratories (figure 65).

Measurements related to power-line environmental impacts — potential

hazards — have been undertaken; they will be treated later in connection with

electromagnetic hazards work.

Measurement support is provided by NBS for industrial development of new transmission technologies, particularly for underground transmission.

These are measurements to aid in the understanding of the processes of insula-

-16-
tion failures. For example, we are developing measurement methodology, based

on both electrical and chemical techniques, to assess the deterioration of

insulating gases in the presence of low-level corona. Analysis of the frequency and the energy distribution of corona pulses is performed; simultaneously, minute chemical changes in the gases are monitored with a mass spectrometer and gas chromatograph (figure 66).

In related work, the electro-optic Kerr-effect and high-speed photographic techniques are employed to diagnose submicrosecond electrical prebreakdown events ("trees" in liquid insulators and at liquid-solid interfaces;

figure 67).

Recently, electronic power-metering instruments (figure 68) have

appeared on the commercial market having stabilities in the field of the order

of +0.1%, an order of magnitude better than traditional electrodynamic

meters. The appropriate NBS services have been improved to provide better

than 0.01% accuracy. For dissemination of standards to this accuracy, the

conventional method of the customer sending his standard to NBS has proved to

be inadequate. A measurement assurance program for this service has been

implemented.

3.5 Electromagnetic Sensing and Hazards

Challenge

We are witnessing in the United States of America a rapid proliferation

of sources of electromagnetic radiation for industrial, safety, law

enforcement, broad-casting, citizens band, and defense applications (figure

69). Examples include over nine million commercial transmitters and 30

million citizens band radios; the 40,000 circuit miles of overhead EHV

electrical transmission lines; an estimated four million microwave ovens; as well as arc welders, combustion engine ignitions, electric motors, and so on.

On the other hand, we are also witnessing an explosion of applications

of electronics: for control of household appliances, transportation systems,

business machines, industrial manufacturing and processing, medical diagnostics, and patient care. All of these electronic controls are susceptible

to interference from stray electromagnetic radiation whose effects may range

from a temporary disruption of function, to subtle alteration of commands in a microprocessor, to complete failure.

Another aspect of the problem is the effect of electromagnetic

radiation on living organisms. While the research results on hazardous

effects of electromagnetic radiation on biological systems are still the

subject of much disagreement, it is becoming increasingly accepted that this

radiation can cause changes, for example, to the nervous sytem and immunological defense systems, at levels below that associated with thermal heating

of tissue.

Electromagnetic radiation is also employed for beneficial uses. There

is increasing recognition that electromagnetic radiation can provide a tool
for the nondestructive evaluation of materials and structures, both manmade

and natural, to determine structural integrity and consequent safety.

Potential applications of this technique include determining coal seam thickness in coal mine ceilings and the curing rate of concrete, detection of flaws

in earthen dams, and sensing of water content of soils and snow.

Common to both the applications of electromagnetic radiation and the

problems resulting from such application is the need for suitable measurement

methods and instrumentation to characterize the electromagnetic environment,

to assess the susceptibility and emission characteristics of electric com- ponents and systems, and to apply electromagnetic radiation for public

benefit. In addition, mechanisms for the delivery of measurement services

must be developed for potential users in governments and in the private sector

to ensure proper application of measurement techniques and instrumentation and

to facilitate compliance with regulations for public health and safety.

NBS Response

The response to the measurement requirements associated with the

effects of electromagnetic radiation on biological systems and electronic

equipment is a growing effort at NBS (figure 70). The heart of the problem

is that there is an inadequate measurement base for determining either the

electromagnetic environment at any point in time or the susceptibility of

electronic systems to the electromagnetic environment. The problem is

complicated by the fact that measurement of amplitude, phase, frequency,

polarization, and spatial coordinates as a function of time is required in

order to obtain an accurate picture of the radiation environment. Typically,

measurements are made of signal amplitude as a function only of frequency.

However, significant information can be lost unless one also measures

frequency response as a function of time (figure 71). Another aspect of the

measurement problem is the need for isotropically sensitive probes.

Instrumentation to make such measurements must be capable of dealing

with complex fields, such as those with reactive near-field components, multipath reflections, arbitrary polarization, multiple frequency components, com- plicated modulations, and large field gradients. No instrument is available

that can actually measure power density in the near field, although this is

the quantity on which most radiation exposure limits are based; no single

probe has been developed that can cover the frequency range of concern (dc to

3000 GHz); nor is there a calibration technique available for present measurement instrumentation.

NBS is currently developing such calibration and measurement techniques, and associated instrumentation, including appropriate probes. For

example, NBS has developed an apparatus, the transverse electromagnetic (TEM)

cell (figure 72), for testing both electromagnetic emissions and susceptibility to electromagnetic interference of equipment placed inside. The cell's

frequency range is from dc to a wavelength which is proportional to the cell's

size. The cell can accommodate a test electronic package as large as one- third the volume of the upper-half space without varying the electric field

- 18-
strength by more than one percent from predictable empty-cell values. This

development has already found wide application in industry. It is also

beginning to find applications in bioeffects research.

To measure electromagnetic fields, NBS has developed several sensitive

electric and magnetic probes in response to the requirements of Federal regulatory agencies concerned with health and safety, and of military agencies

concerned with weapons reliability. Examples include the following: for the

National Institute for Occupational Safety and Health, electric- and magneticfield probes for the frequency ranges 10 MHz to 500 MHz and 10 MHz to 40 MHz,

respectively; for the Bureau of Radiological Health, an isotropic hazard meter

with a frequency range of 300 MHz to 3GHz; and for the military, and electromagnetic monitoring system, covering the range 10 KHz to 18 GHz, to protect

sensitive electronics in weapons. This monitoring system has been engineered

for easy adaptation to commercial manufacture. It may also serve as a hazards

monitor for safety in the industrial workplace. Most recently, NBS has incorporated three tiny dipole-diode field sensors, in an orthogonal array (figures

73 and 74), to provide an electric-field probe designed to operate from 500

kHz to 1 GHz. It is 100 times more sensitive than commercially available

units. This probe (figure 75) was specifically designed and engineered for

commercial manufacture to encourage its use.

In related efforts, mentioned earlier, we are working with the Department of Energy to ensure accuracy of measurements of electric and magnetic

fields and ion currents in the vicinity of actual high-voltage transmission

lines (figure 76) and in simulated environments where studies are conducted on

the bioeffects of these 60-Hz fields; and for the Bureau of Radiological

Health, we provide the measurement services and calibrations underlying the

enforcement of Federal safety regulations covering lasers.

NBS is concerned with the correlation of electromagnetic scattering

properties with material and structural properties such as moisture content,

stratification, and porosity so that electromagnetic scattering measurements

can be better applied to testing of materials and structures.

An example is the application of electromagnetic measurements to re- quirements in the mining of coal (figure 77), underlying both mine safety and

energy production. NBS has developed a radar-like technique (figure 78) based

on the relationship of the physical properties of the various strata and

structures found in mines to changes in phase and amplitude between the propagating and reflected radiation. This technique can be used to determine the

structural integrity of the coal mine shaft or tunnel. NBS is working directly with other Federal agencies to assure transfer of this technology to

application in automated coal-mining equipment.

4. CONCLUSION

Let me conclude by expressing the hope that I have made my message

clear: While the provision of traditional metrological standards and services

is the foundation of national and international measurement systems, new demands and opportunities face those responsible for the success of such

-19-
measurement systems. Rapidly advancing technology, and its impact on science,

industry, and governmental functions, bring with them demands on measurements

for research, manufacture, procurement, and regulation which go beyond

traditional concerns of metrological organizations. Yet these organizations,

I believe, have a responsibility, a knowledge, and a dedication with respect

to the science and technology of measurement, that transcend those of the

organizations which desperately need new practical measurement capabilities

beyond those now available to them. Thus it is that metrologists should look

to the emerging needs and provide the exciting new methods, standards, and

services required. My examples from the work at NBS give just a flavor of the

way one national laboratory dedicated to metrology is addressing these

challenging measurement problems.

Acknowledgment

The assistance of members of the Center for Electronics and Electrical

Engineering in the preparation of this review is gratefully acknowledged. The

aid of W.M. Bullis, R.A. Kamper, C.K.S. Miller, 0. Petersons, J.F. Mayo-Wells,

and C.E. Hood is particularly appreciated.

-20-
NEW TECHNOLOGY CHALLENGES METROLOGY

Figures 1-78

-23-
NATIONAL BUREAU OF STANDARDS

LEGAL

PUBLIC

AFFAIRS

DIRECTOR

Deputy Director

OF THE DIRECTOR

NBS/BOULOER

NATIONAL

ENGINEERING

LABORATORY

NATIONAL

MEASUREMENT

LABORATORY

INSTITUTE FOR

COMPUTER

SCIENCES ft

TECHNOLOGY

NOV. 13, 1978

Fig. 3 NBS Organization chart.

-24-
NATIONAL MEASUREMENT

LABORATORY

CENTERS

Absolute Physical

Quantities

Radiation Research

Thermodynamics &

Molecular Science

Analytical Chemistry

Materials Science

NATIONAL ENGINEERING

LABORATORY

CENTERS

Applied Mathematics

Electronics & Electrical Engineering

" Mechanical Engineering &

Process Technology

Building Technology

Fire Research

Consumer Product Technology

INSTITUTE FOR COMPUTER SCIENCES

AND TECHNOLOGY

CENTERS

Programming Science & Technology

Computer Systems Engineering

Figs. 4,5,6 Major organizational constituents

(centers) of NBS National Measurements

Laboratory, National Engineering

Laboratory, and Institute for Computer

Sciences and Technology.

-25-
Office of Measurement Services

• Calibration Services

• Measurement Assurance

Programs

• New Measurement

Requirements

Office of Standard Reference Materials

• Coordination of research and

production of Standard Reference

Materials

• Sale of Standard Reference Materials
CENTER FOR Provides focus in NBS

ELECTRONICS •Research, development

AND ELECTRICAL and applications

ENGINEERING . Electronic and electrical

materials and

engineering

CENTER FOR

ELECTRONICS AND

ELECTRICAL ENGINEERING

Provides

Measurement

methods

Data

Standards and

traceability

Technology

Technical

services

To

Government

Industry

Scientific

community

For

Trade

Manufacture

Application

CEEE Programs

• Semiconductor Technology

• Fast Signal Acquisition and

Processing

• Fast Signal Transmission

• Electrical Systems

• Electromagnetic Sensing

and Hazards

Figs . 10,11,12 The Center for Electronics and

Electrical Engineering's focus,

services, clientele, and technical

program areas .

-27-
SEMICONDUCTOR Significance

TECHNOLOGY • Underlies the electronics

revolution; central to success

of industrial societies

• Metrology required for

manufacturing control and

the marketplace exceeds

the state of the art

SEMICONDUCTOR NBS Response

TECHNOLOGY • Measurement methods for: — Semiconductor material

properties — Process and assembly

control — Device testing

• More effective means to

disseminate the methods

Figs. 13,14 Semiconductor Technology Program - metrological significance and

challenge and NBS response.

-28-
Fig. 15 The starting material for integrated

circuits: a single-crystal ingot of

high-purity silicon, and slices.

-29-
OPTICAL IMAGE PROFILE

MATERIAL PROFILE

_£

Fig. 16 Uncertainty in the definition of edges in

the optical image profile of material

steps

.

-30-

)
LINEWIDTH: WM

= (X 2 — A) — {X, + A ) = X 2 — Xi —2

A

PITCH: P = (X! + A) - (X 3 + A) = Xi - X 3

Fig. 17 Measurements of linewidths are subject to

edge uncertainty A, whereas measurements

of pitch are not.

-31-

NBS-deve loped automatic scanning

photometric microscope for linewidth

measurement

.

-33-
-1.0 0.5 0.5 1.0 DISTANCE /* m

20 Comparison of theoretically predicted

profile (smooth line) with profile

obtained with the photometric microscope.

-34-
Fig. 21 Dissemination is an important part of CEEE

programs. This photograph was taken

during a special training seminar on

linewidth measurement attended by

industrial representatives who need to be

able to make the measurement in their

daily work.

-35-
01234 56789

I-I-I-I-a-I-I-I — -1- - -B-|.| — "I" E

0 12 3 4

III -l-c

5 6 7 8 9

-l-l-l-l-l-

-l-D-l i-l-J0 2 3 4 5 6 7 8 9 —I"H"I— NH"H«I -E- |"iHl| H"H"H"|—

3 4

-++

0 1 —iiiiiii —mill g

Fig. 22 One of the measured and calibrated

linewidth patterns forming part of

standard reference material 474.

-36-
(II TMm Kl COMMENDED PROCI DURES

fmt FOR PHOTOMASK I.INEWIDTH MEAS U Ri Ml MS

(AR - CHROMIUM)

National Bureau of Standards Washington, D.C. 20234 4

<g| DRAFT JANUARY 1980

II

>

Fig. 23 Measurement procedures are part of the

documentation furnished as part of

standard reference material 474.

-37-
Fig. 24 A test structure for determining

registration errors between selected mask

levels in a semiconductor device

fabrication process. Electrical

measurements are used to determine

mechanical parameters.

-38-
Fig. 25 View through a microscope of a wafer

prober in operation.

-39-
CONTACT TO BASE ALIGNMENT

ORIGINAL DATA TRANSLATION AND

ROTATION REMOVED

5 Mm 5 jjm

Fig. 26 A computer-generated map of registration

or alignment errors demonstrates the

existence of significant distortions (on

the order of 1 Urn ) in wafer or mask, or

both, when translation and rotation errors

are computationally removed.

-40-

Fig. 28 A single test pattern from the wafer of

figure 27. The pattern is made up of a number of individual test structures for

measuring various parameters, including

bulk resistivity and dopant- impurity

density

.

-42- )
10^1

SURFACE ANGLE LAP & STAIN ANGLE LAP 8. STAIN

Fig. 29 In actual devices, very large changes in

dopant impurity concentration occur over

very small dimensions.

-43-
MOSFET D-C DOPANT PROFILES

SOURCE-BODY VOLTAGE VC, B

GATE-SOURCE VOLTAGE, V

N m (wm )= -ttzytz-*)

Fig. 30 A metal oxide-semiconductor (MOS)

structure (on right) for measuring dopant

impurity concentration profiles.

-44-
GATED-DIODE MOSFET AMPLIFIER

VB VR

ct>R VG

OUTPUT

MOSFET

MOSFET SWITCH

GATED

DIODE

100 Mm

11 SOURCE/DRAIN

HI POLY SILICON

EH SUBSTRATE

CONTACT

METAL

Fig. 31 An MOS structure incorporating a "throwaway" electrometer for measurements of

charge carrier lifetime, a parameter that

relates to the number of defects or

impurities present in the crystal.

-45-
U3dVM SS0H3V NOIllSOd

r

o

CM

o

LU

ILU

© r> n in t

fV_ ^4 _« >4 ©

•

VU &) H | >•>

i +>

rnUi

/ii w

1 \ +J

tin

(/}

1

1

\ w

PH vuE

ll mUJ r i I,M H

0) i \ 4~> fyfrt Ui

/ii QJ

c; Q)

Q)

• t =M

C3B

*H In

1

1

f\\ \V 'Pi M-l tfi ,_j •n H

( |

fi\

ll 1 M—

1

rrf f\\J ipI E

Q.

rrl <y G M

ill rrl

t\) w

i \ in

frl <U

t +J

liM r1

(\\ w rtl c;

d)In tiM

«—

(0

(0 -P <De

ftg

0 W O 0)

r3 Eh

(srl) <3I/Mll3dn> ui n

oj ro

<*4

of., x < X <

< X -< X

r- +

+

LU

yy

Ll,

CO

•rH fa V

-46-
FAST

SIGNAL

ACQUISITION

AND

PROCESSING

Significance

• Digital signals underlie the electronic

information and control revolution,

with impact akin to the industrial

revolution

• Traditional metrology is inadequate

to assure in-situ accuracy of high

speed instruments, automatic test

equipment, and "gigabit electronics".

FAST

SIGNAL

ACQUISITION

AND

PROCESSING

Key Factors

• Automation of calibration

• Software

• Traceability

• New physical standards

• Broadening range of key

parameters

• Emerging technologies

• Improved dissemination

of standards

FAST

SIGNAL

ACQUISITION

AND

PROCESSING

NBS Response

• New physical reference standards

(For analog/digital equipment,

waveform sources, etc.)

• Extension of frequency and timedomain coverage (0.1 Hz sinewaves,

picosecond pulses, etc.)

• New dissemination methods

(Transport standards, etc.)

Fig. 33,34,35 Fast Signal Acquisition and

Processing Program - metrological

significance and challenge, key

factors, and NBS response.

-47-

The NBS Super DAC : a 20-bit reference

digital-to-analog converter. This

instrument is used in the characterization

of static performance parameters of

analog-to-digital converters.

-49-
Fig. 38 A developmental test facility for

calibrating static performance parameters

of analog-to-digital converters. The

reference Super DAC is at the bottom of

the right-hand equipment rack.

-50-
Fig. 39 Implementation of programmable audiofrequency phase-angle standard. Component

circuit boards are visible at the left;

the oscilloscope displays the output

sinewaves displaced in phase.

-51-
Digital technology makes possible this NBS

low-frequency (0.1-Hz) voltmeter. One

application is the measurement of seismic

response of structures.

-52-
1 One version of the NBS Automatic Pulse

Measurement System for determining

waveshape of signals from nanosecondduration events.

-53-
NBS- deve loped impulse generator based

tunnel diode and a Debye-liquid delay

line.

-54-
NBS time-domain antenna range and

Automatic Pulse Measurement System (at the

left). The half-conical launching antenna

can be seen near the center of the

photograph. The test antenna is mounted

on wooden blocks just above the ground

plane .

-55-
Fig. 44 Schematic of Josephson Junction

-56-
- 1

—_«i—i —«—i

ji • •q'-f—

j

M» M|

Wmm M1 1I ' ' 11

Fig. 45 Photograph of four-bit, very-high-speed,

superconducting analog-to-digital

converter. Three Josephson junction

interferometers are used to encode each

bit

-57-
Developmental model of S t i r 1 in g- cy c le

mechanical refrigerator. Two units in

cascade are capable of reaching liquid

helium temperatures.

-58-
FAST Significance

SIGNAL # Digital and optical electronics,

TRANSMISSION satellites, optical fibers and lasers are radically changing telecommunications, navigation, and

remote sensing

• Metrology is challenged by

demands for - Increasing dynamic range,

spectrum, and time-domain

resolution of signals - Test methods to characterize

new components of transmission

systems

FAST NBS Response

SIGNAL m Automation, extended ranges,

TRANSMISSION new methods and dissemination

services for measurements of - Microwave and millimeter -wave

components - Antennas - Satellite ground stations - Optical fibers - Lasers

Figs. 47,48 Fast Signal Transmission Program - metrological significance and

challenge and NBS response.

-59-
Fig. 49 Manually tuned microwave calibration rig

for two-port linear devices.

-60-
Fig. 50 Automatic Network Analyzer (ANA) for

making the same measurement depicted in

figure 49, but at a rate that makes

practical complete mapping of specimen

device performance over its specified

frequency range.

-61-
e ANY LINEAR

6-PORT JUNCTION

b/a | e

a

r

at

2

I a. P.

i=3 11

= S3

P

a b I cos ]b = Zc . P .

1 r -,

-j

a b I cos \p = Is

Fig. 51 6-port principle: only simple power

measurement - not phase - are required to

determine the reflection characteristics

at the unknown port.

-62-
MEASUREMENT SETUP

Fig. 52 Schematic of the dual 6-port ANA, an NBS

development. The unknown is the device

marked "2-port".

-63-
Implementation of the dual 6-port ANA as

practical, stable, and accurate

calibration tool. Scattering parameters,

quantities of great interest to microwave

design engineers, are directly measured.

-64-
Fig. 54 NBS calibration facility for near-field

scanning of antenna pattern.

-65-

-16 0 16

ELEVATION ANGLE IN DEGREES

Fig. 56 Computer-generated plot of calculated farfield pattern for antenna measured in the

near field. A major NBS contribution has

been the development of the theory

required to transform near-field

"measurements to far-field pattern.

-67-
Fig. 57 Interior of satellite communication ground

station, the noise performance of which is

being checked with a radio star as

reference.

-68-
Fig. 58 An illuminated spool of optical fiber.

-69-


ELECTRICAL Significance

SYSTEMS • Energy crisis and environmental

concerns force new developments

in electrical distribution systems

• Improved metrology is essential for - Higher voltages - Environmental effects - New transmission line technologies - Network transients - Variable-rate low power metering

ELECTRICAL

SYSTEMS

NBS Response

• Increased range, in-situ calibration

services for high power metering

• New test methods for electromagnetic

fields near transmission lines • Test methods and data for new

underground transmission systems

• Improved accuracy, new measurement

assurance program for low power

metering

Fig. 61,62 Electrical Systems Program - metrological

significance and challenge and NBS

response
Fig. 63 Capacitive coupling voltage transformers

on site at electric utility substation.

-73-

Fig. 65 NBS measurement of a very-high-voltage

device in a French laboratory. The NBS

apparatus appears as a small spool-shaped

object at the center right of the

photograph. Note the size of the

stepladder and the person at the equipment

rack .

-75-
c

-H •

05 tji -P C U -H 3 U ^ r4 O nj M

ft 03

(0 c> ,C O V

03

(d ~

0)

r4

0)C fd H u ^ -H d n

0) P

(du

<D 0> £ rH o o

•4-1

p

0)

p 0 O

+J a>

(0 -n ^ 43

CO 3

ft 03

<0 03

(d

Ou

C

•rH -H

-P P

fd fd E rH

d) 3 ^ 03 O C

CO -H

IX)

•H

-76-
CATHODE POINT

Fig. 67 Diagram showing a breakdown event in a liquid insulating material between a point

and a plane.

-77-
Fig. 68 An electronic watthour meter. This

instrument requires a ten-fold improvement

in accuracy of calibration compared to the

requirements of previous electrodynamic

designs

.

-78-
ELECTROMAGNETIC

SENSING

AND

HAZARDS

ELECTROMAGNETIC

SENSING

AND

HAZARDS

Significance

• Proliferation of electromagnetic (EM)

radiation sources has created concern

for interference with key electronic

systems and for hazards to humans

• EM radiation can serve as a non-destructive

probe for structural integrity and safety,

and water resource management

• Metrology is now inadequate to - Characterize the EM environment - Assess EM susceptibility and emission

of electronic components and systems - Apply EM radiation for non-destructive

evaluation of structures and materials

NBS Response

• Provision to industry and regulatory

agencies of measurement techniques

covering critical frequency and power

density ranges to characterize EM

interference and hazards

• Correlation of EM properties of selected

natural and structural materials with their

physical properties as bases for nondestructive evaluation of integrity and

safety and water resource management

Figs. 69,70 Electromagnetic Sensing and Hazards

Program - metrological significance

and challenge and NBS response.

-79-
Fig. 71 Adequate characterization of the

electromagnetic fields present in real

situations of practical interest (e.g., in

cities) requires mult ispectral

measurements over time and frequency.

-80-
Fig. 72 Three transverse electromagnetic (TEM)

cells. TEM cells provide a wellcharacterized field over a useful volume

and are used for both susceptibility and

emission measurements. The cells operate

over a frequency range from dc to an upper

limit proportional to cell size.

-81-
Fig. 73 Photograph of dipole-diode array for

isotropic measurement of electric field

strength. This antenna and an associated

electronics package constitute the NBS

EFM-5 probe, now available commercially.

-82-

<
Dipole

High -resistance line

Diode

(a) Schematic of dipole -

diode field sensor.

Fig. 74 Dipole-diode electric field sensor

-83-

Fig. 76 Measurement of electric fields resulting

from high-voltage transmission lines,

this measurement is sensitive to the

presence of the operator, hence the long

handle

.

-85-
Fig. 77 An NBS-developed instrument for measuring

the roof thickness of a mined coal seam.

The mine operator desires to remove as much coal as possible, but to leave a thick enough roof layer to support the

overlying slate and to protect it from

weathering. Common practice is to leave

more coal than is required to safety, on

the basis of both experience and the use

of small test bores in which a direct

measurement may be made.

-86-
0

-p

T3

CD <D X CO P 3

<+h co O -H Co

•H -H • -P -P E

n) io

u

>H -H +J

<U T3 CO Gi <d > O P co

MH

U

O «H

-p

CD CD rH C

&, Cn H <d U g C 0

•H Vh P 4->

<U rH X w

-pC r- H r-

-p

(0 (1) p p P 3

CO tT> 3 -H

rH IW rHH CH

id c P 5

tx>

O

m

x

cu • X cu •H rH

rH XI I H

in CO

(3 CO0

H3 &| P

CO

r0 •H

rH

<GU

•H

+>

<TJ &

CDu

CO

ccrCP

•H

C CO •H CO

co c p

cu

u

>i -H

(0 XI

rH 4->

cu E

-P (0

(0 <u rH 10 CO rH

T3 03 C O

<d

u

rH 0 o

«4HO

CTcHC

a.

CD X

4J

CD0P& E

-87-
NBS-114A (rev. 2-eo

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS SP 611

2. Performing Organ. Report No 3. Publ Ication Date

July 1981

4. TITLE AND SUBTITLE

New Technology Challenges Metrology

5. AUTHOR(S)

Judson C. French

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

National Bureau of Standards Organization of American States

Department of Commerce 19th Street & Constitution Avenue

Washington, DC 20234 Washington, DC 20037

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 81-600063

_J Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most s i gn i fi cant information . If document includes a si gnificant

bi bl iography or literature survey, mention it here)

Assurance of measurement quality to meet requirements for regulatory agencies,

marketplace equity, and productivity and quality control in manufacturing and

research is challenged by unprecedented demands for sensitivity, speed, precision,

and accuracy over wide ranges of properties and signal characteristics. New

approaches are needed. Examples of NBS response, principally in electrical and

electronic engineering, are described.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize on^^y—proper names; and separate key words by semicolons)

calibration; electrical; electronics; engineering; hazards; measurement^- metrology

National Bureau of Standards; power; radiation; semiconductor; technology

13. AVAILABILITY

\^T\ Unl imited

|

| For Official Distribution. Do Not Release to NTIS

Fjn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

~J Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

90

15. Price

$4 . 50

USCOMM-DC 6043-P80


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