c* NIST SPECIAL PUBLICATION 400-98

U.S. DEPARTMENT OF COMMERCE/Technology Administration

National Institute of Standards and Technology

ent Techno

Survey of Optical Characterization Methods for Materials,

Processing, and Manufacturing in the Semiconductor Industr

z, and D. G. Seller
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Semiconductor Measurement Technology:

Survey of Optical Characterization Methods for Materials,

Processing, and Manufacturing in the Semiconductor Industry

W. Murray Bullis

Materials and Metrology

Sunnyvale, CA 94087-4015

S. Perkowitz

Emory University

Atlanta, GA 30322-2430

D. G. Seiler

Semiconductor Electronics Division

Electronics and Electrical Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-0001

December 1995

U.S. DEPARTMENT OF COMMERCE, Ronald H. Brown, Secretary

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Arati Prabhakar, Director
National Institute of Standards and Technology Special Publication 400-98

Natl. Inst. Stand. Technol. Spec. Publ. 400-98, 50 pages (December 1995)

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1995

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
TABLE OF CONTENTS

Page

Abstract i Key Words 1 Background of Survey 2

Introduction to Optical Characterization 3

Ellipsometry 3

Infrared Spectroscopy 3

Interferometry 4

Modulation Spectroscopy 4

Optical Microscopy 4

Photoluminescence 5

Raman Scattering 6

Reflectometry 7

Scatterometry 7

Distribution of Survey Responses 7

Use and Value of the Methods 9

Properties Characterized 10

Measured Materials and Devices 10

Range and Precision 14

Comparison to Other Methods 17

Cost Issues 20

Comments from Respondents 20

Summary 21

Acknowledgments 22

References 22

Appendix A - Initial Survey Form 25

Appendix B - Expanded Survey Form 35

Appendix C - Bibliography 47

iii
LIST OF TABLES

Page

L Reported Usage of Optical Characterization Methods in Five Steps of the

Research-to-Product Cycle 8

IL Use and Value of Optical Characterization Methods 8

in. Material Properties Measured by Optical Methods, Listed Alphabetically by

Technique 11

IV. Relative Usage of Optical Characterization Methods on Materials and Devices . . 12

V. Materials Reported to be Characterized by Optical Methods 13

VI. Applications of Optical Characterization Techniques to Electronic and Photonic

Devices 14

VII. Range and Precision of Measurements, and Maximum Sample Area Examined . . 15

VIII. Degree of Respondents' Satisfaction with Selected Attributes of Optical Methods for

Characterizing Various Material Properties 16

IX. Degree of Use and Satisfaction with Other Attributes of Optical Characterization

Techniques 16

X. Reasons for Selection of Optical Methods over Other (Non-Optical) Techniques to Measure a Given Material Property 18

XI. Reasons That Optical Characterization Methods Are Not Used 18

XII. Source of Optical Characterization Equipment Used in the Semiconductor

Industry 19

XIII. Costs Associated with the Use of Optical Characterization Equipment in the

Semiconductor Industry 19

iv
Semiconductor Measurement Technology:

Survey of Optical Characterization Methods for Materials, Processing,

and Manufacturing in the Semiconductor Industry

W. M. Bullis

Materials & Metrology, Sunnyvale, CA 94087-4015

S. Perkowitz

Department of Physics, Emory University, Atlanta, GA 30322-2430

D. G. Seller

National Institute of Standards and Technology, Gaithersburg, MD 20899

A preliminary report on this survey was presented at the International Workshop

on Semiconductor Characterization: Present Status and Fumre Needs, January

30 to February 2, 1995, in Gaithersburg, Maryland (Reference [1]).

ABSTRACT

Contactless, nondestructive optical methods are used to characterize many critical

properties of materials, processes, and devices in the semiconductor industry. To

determine the extent of use and the relative importance of various optical methods

in the industry, the Semiconductor Electronics Division of the National Institute

of Standards and Technology conducted a survey of this field. The survey also

sought to identify both advantages and limitations of these techniques as well as future requirements for and anticipated use of optical characterization methods

within the semiconductor industry. Data from 42 firms were analyzed to show

the impact of the methods, what they measure, their range and precision, and

their cost. A significant finding of the study is the need expressed by many

industrial users for improved standards and test methods for optical

characterization, especially in the area of film thickness and composition.

Key words: compound semiconductors; ellipsometry; infrared spectroscopy;

interferometry; optical characterization; optical microscopy; photoluminescence;

photoreflectance ; Raman scattering ; reflectometry ; scatterometry ; semiconductors

;

silicon

1
BACKGROUND OF SURVEY

Many different methods are used for the characterization of materials and devices in the

semiconductor industry. Among these, optical methods offer significant advantages compared

to other techniques because they do not require the application of electrical contacts or other

special sample preparation [2] [3]. Because of the remote nature of optical probes, test samples

or product wafers can be examined in situ during device processing. The probe beam can be

focused to a small spot and scanned, allowing different regions of a sample to be characterized

and maps of various properties to be produced. A recent workshop on the manufacture of

integrated circuits noted that in-situ or real-time metrology is critically needed for the next

generation of devices [2]. It also called for the development of new optical techniques, such as means to analyze and image an entire wafer surface to determine spatially resolved etch rate and

end-point determination.

In response to such statements of industrial need, and growing out of its involvement with

optical characterization methods such as ellipsometry, infrared absorption, and others, the

Semiconductor Electronics Division of the National Institute of Standards and Technology

(NIST) undertook to survey the extent of industrial use and relative importance of optical

characterization methods in the semiconductor industry.

A questionnaire was designed by consultation among semiconductor scientists working

at NIST, in industry, and in academia, to determine the advantages, limitations, and utilization

of nine optical characterization methods: ellipsometry, infrared spectroscopy, interferometry,

optical microscopy (visible and infrared), photoluminescence, photoreflectance, Raman

scattering, reflectometry, and scatterometry. These were chosen because of their known or assumed value in characterizing semiconductors for electronic and photonic devices. Combined,

these methods measure most of the properties that are important for such devices. This

questionnaire is reproduced in Appendix A. It was sent to about 75 key individuals in U.S.

industrial concerns that manufacture materials for devices, the devices themselves, or equipment

to characterize or process semiconductors. This initial questionnaire was returned by 23

respondents.

Later, a slightly expanded version of the questionnaire, identical to the initial questionnaire except for additions to two of the questions, was developed. The additions were

designed to elicit additional information about where and how optical characterization methods

are applied in the industry. This version was distributed to nearly 75 more individuals in the

industry in order to supplement the initial survey. A copy of this expanded questionnaire is reproduced in Appendix B. Nineteen respondents returned the expanded version of the

questionnaire.

2
This report presents an analysis of the data from all 42 responses. Most of the

information reported is based on the portions of the two versions that were identical. Additional

data from the expanded version of the questionnaire are used to supplement the basic

information. To facilitate further investigation of optical characterization technology, a literature

base consisting of useful general surveys, and applications to specific materials and

characterization problems is provided as Appendix C.

INTRODUCTION TO OPTICAL CHARACTERIZATION

Optical characterization principles, methods, and applications to the field of

microelectronics and semiconductors have recently been reviewed [3] [4]. This section briefly

describes nine of the most widely used optical techniques (ellipsometry, infrared spectroscopy,

interferometry, modulation spectroscopy, optical microscopy, photoluminescence, Raman

scattering, reflectometry, and scatterometry) to provide a background and framework for the

reader in order to better understand the results of the optical characterization survey.

Ellipsometry

Ellipsometry is based on the polarization transformation that occurs when a beam of

polarized light is reflected from (or transmitted through) an interface or film [5] [6]. This

technique widely used to measure the thicknesses and optical constants of films important to semiconductor technology, such as Si02 on Si. Thicknesses measured are typically in the range

of several nanometers to several hundred nanometers. Surface cleanliness of semiconductor

wafers during processing can also be determined. In spectroscopic ellipsometry, the

ellipsometric data are obtained as a function of wavelength. Then appropriate modeling and

fitting can yield the dielectric functions and thicknesses of the layers in complex

semiconductor/oxide multilayer systems. The dielectric functions give a complete picture of

composition throughout the entire layered structures.

Infrared Spectroscopy

Infrared (IR) radiation interacts with semiconductor lattices, carriers, and impurities, and

absorption in a uniform semiconductor layer is proportional to the layer thickness [7] . Infrared

spectroscopy can then be used to determine impurity type and concentration in semiconductor

materials, film thickness, semiconductor alloy composition, carrier density, and scattering time.

These measurements can be made for bulk, film, and microstructure systems. In one application

in Si, the amount of interstitial oxygen, whose concentration is critical, is determined from IR

absorption [8]; correct values provide gettering action, reducing the level of other impurities,

and hence, producing material with low leakage currents.

3
Interferometry

Interferometers are used to measure distances from a reference surface [9]. This type

of instrument can be used directly in geometrical measurements such as the profile of an object

such as a wafer or the flatness of a wafer surface. On a microscale, interferometers are used

in surface texture instruments that observe areas ranging from a few hundred micrometers on

a side to several millimeters on a side. An interferometer is also an integral component of one

type of infrared spectrophotometer, the Fourier Transform Infrared (FTIR) spectrometer [7].

Modulation Spectroscopy

Modulation spectroscopy is a sensitive technique that can determine fine details of

interband transitions in semiconductors. In semiconductor superlattices and other

microstructures, detailed knowledge of the complex interband transitions can be used to characterize quantum well widths, potential barrier heights and widths, electric fields, the

amount of strain in strain layer systems, and doping densities.

The principle behind modulation spectroscopy is that a periodic physical perturbation

applied to a sample elicits the derivative of the sample's optical response to that perturbation.

The derivative feature amplifies weak features in the response function and suppresses large

constant background levels. This gives modulation methods very high sensitivity to small

spectral features that are invisible in conventional spectroscopy.

Examples are electroreflectance, where a periodic electric field is applied to a sample

while its reflectance spectrum is measured; and photoreflectance, where optically injected

carriers from a chopped laser beam modulate the "built-in" surface or internal electric fields,

thus modulating the reflectance of the sample. Other forms of modulation spectroscopy have

been reviewed by Aspnes [10].

Optical Microscopy

Traditional optical microscopy is useful for a large number of applications such as examining topological features larger than —1.0 fim, examining defects, or counting etch pits

[11]. Several specialized forms of optical microscopy are highly valuable: Nomarski, scanning

laser, and microspectrophotometry. In Nomarski microscopy, interference methods are used to increase the contrast between small differences in the surface level of a semiconductor wafer.

Scanning microscopy in both the visible and infrared spectral ranges allows two-dimensional

imaging of features in a layer or structure. Finally, microspectrophotometry allows film

thickness determination from spectral analysis of reflected light.

Scanning microscopy is also used in both the visible and the infrared spectral ranges to form two-dimensional images of inhomogeneities in a semiconductor. The form called confocal

4
microscopy produces three-dimensional images. One visible light-scanning technique of special

interest is the optical-beam-induced current method (abbreviated OBIC, or sometimes LBIC, for

laser-beam-induced current), which detects grain boundaries, dislocations, and other defects in

semiconductors and semiconductor devices. OBIC images represent spatial distributions of

electrically active defects that include inclusions, strain, damage, precipitates, stacking faults,

twin boundaries, dislocation clusters, and bandgap and doping variations.

Near-field scanning optical microscopy (NSOM) has recently been shown to be able to optically resolve feamres smaller than the diffraction limit. NSOM exploits the optical

interaction arising from a sharp probe (optical fiber that terminates by tapering into a fine

truncated cone) in close proximity to a sample in order to image the surface. This sharp probe

is freely positioned or raster scanned across the surfaces, allowing highly localized exposures

of the sample or generation of high-resolution images. Future work will determine the

usefulness of NSOM in microelectronics manufacturing and its niche among competing

technologies.

Photoluminescence

Photoluminescence (PL) depends on the fact that electrons residing in the valence band

of a semiconductor can be excited via optical absorption to the conduction band, to an impurity,

or to a defect level in the energy gap. PL results from radiative relaxation of an optically

excited population, in which an excited electron usually returns to its initial state after a short

time. If the excited electron returns to its initial state by radiative means, the process emits a photon whose energy is the difference between the excited and the initial state energies. The

spectral distribution of the emitted photons shows an emission peak at the energy (or wavelength)

corresponding to each excited level [12].

Photoluminescence can be used to determine the energy gap of a semiconductor sample.

This technique is especially useful for III-V and II-VI ternary alloys like Al^Gaj.xAs and

Zn^Cdi.^Te, because the energy gap, which varies with the compositional parameter x, must be

accurately known for most applications. When this process is inverted, x can be found from the

gap value and the known relation between gap energy and composition. Photoluminescence also

detects the presence of impurities and crystalline defects in semiconductors that affect materials

quality and device performance. Each impurity produces a characteristic feature or set of

features in the spectrum. Hence, the impurity type can be identified, and multiple impurities can be detected in a single PL spectrum. In some cases, PL can measure the concentration of

impurities. Comparison of PL peak halfwidths from sample to sample gives an indication of

impurity concentration, carrier concentration, and crystal perfection. It is often necessary to cool the sample below room temperature to observe the best PL spectra. Cooling reduces the

5
thermal broadening of the excited carrier spectrum of the order IcbT, and also reduces the

importance of nonradiative de-excitation processes.

Raman Scattering

Raman scattering results when photons interact with optical lattice vibrations (phonons)

of a semiconductor crystal lattice. It is a two-photon process, and is thus more complex than

one-photon optical processes such as photoluminescence. If light impinges on the surface of a semiconductor, a large portion is reflected, transmitted, absorbed, or elastically scattered

(Rayleigh scattering), with no change in frequency. A small part of the light interacts

inelastically with phonon modes, so that the outgoing photons have frequencies shifted from the

incoming values. These are the Raman-scattered photons. Since the photons can either gain

energy or lose energy in their phonon interactions, the scattered light can be of higher frequency

(anti-Stokes-shifted) or of lower frequency (Stokes-shifted) than the incident light. Because of

statistical considerations, the Stokes modes are stronger and are usually the ones observed in

Raman measurements at room temperature [13].

The way in which these phonons appear in a Raman spectrum depends on the crystallinity

of a sample and on its crystal orientation. Hence, Raman scattering can determine whether a sample is amorphous or crystalline, and whether the crystal is of good quality or is altered by

damage or imperfections. The method is also sensitive to strain effects, which change

semiconductor lattice structure and hence, phonon frequencies. Since phonon frequencies and

amplitudes in an alloy semiconductor like Al^Gai.^As change with the degree of alloying, Raman

scattering can be used to measure composition as well. By changing the wavelength of the light

exciting the scattering, the penetration depth can be changed, which gives the capability to probe

layered or inhomogeneous structures.

In microprobe Raman scattering, a microscope is coupled to the Raman system, making

it possible to probe regions as small as ~ 1 fxm across. This allows for the identification of

contaminating impurities in extremely small regions of the specimen. In resonance Raman

scattering, the scattering process is strengthened when the incoming photon energy matches the

energy gap or other higher-order critical point energies in the sample's band structure. This resonance strengthens the inherently weak Raman process and also gives band structure information as well as phonon information.

Raman scattering has also been used to measure the temperature of semiconductor

samples.

6
Reflectometry

Reflectometry is the workhorse technique for routine measurements of film thickness in

the manufacture of silicon devices and circuits. It is based on the interference phenomena

associated with reflection of a light beam from optical interfaces between two materials with

different dielectric constants. Although not generally as powerful a technique as ellipsometry,

refmements in optical models allow the rapid determination of layer thicknesses in single and

multiple film stacks.

Scatterometry

Scatterometry is based on the measurement of the amount of light scattered from a

surface. From this measurement, surface defects, surface topography, and subsurface defects can be evaluated [14]. Both integrating and angle-resolved scatterometers are employed.

Integrating scatterometers have been used for more than a decade and a half for rapid and

routine location of particulate contamination and other surface defects as well as for

quantitatively determining the background scatter or "haze." More recently, andle-resolved

scatterometry, long used in the optics industry for charactering very smooth surfaces, has begun

to be applied to analysis of the surface texture of polished semiconductor surfaces.

DISTRIBUTION OF SURVEY RESPONSES

The number of survey responses and their distribution among types of firms represent

a broad, but not completely representative, view of the semiconductor industry. Of the 42

responses, 17 came from materials suppliers, 13 from device manufacturers, and 12 from

equipment suppliers, primarily makers of characterization equipment rather than processing

equipment. Both small and large enterprises were represented. Different stages in the researchto-product cycle were also represented, as was determined by a question in the expanded version

of the questionnaire that asked where in the cycle the optical methods are used. The results

appear in Table I. The heaviest use comes in the areas of research and development and of

process development so the survey overwhelmingly represents the pre-production portions of the

cycle. Although some usage was reported for off-line diagnostics, quality control, and process

control, the results are biased so that neither the requirements for nor the extent of the use of

these techniques in materials and device production environments are fully indicated.

It should also be noted that the data reported here represent a mixture of responses from

users of various materials. Thirteen of the responses came from users in the silicon industry,

11 from the III-V compound semiconductor area, six from the II-VI compound semiconductor

area, and one from the flat-panel display area. Three of the responses did not provide

information regarding the nature of materials characterized. Since test equipment can generally

7
Table I. Reported Usage of Optical Characterization Methods in Five Steps of the Research-toProduct Cycle

Optical Method

Research & Process

Development Development

Off-Line \^ II L 1 1 1 C Diagnostics

0\ 1?^ Iit\/ Control

11 L/UtJoo

Control

Ellipsometry 1

1

6 6 10

Infrared Spectroscopy 7 8 4 4 5

Interferometry 4 2 1 2 3

Optical Microscopy 9 5 5 5 6

Photoluminescence^ — — —

Photoreflectance 2 1 1 1 1 Raman Scattering 1 2

Reflectometry 7 5 4 2 4

Scatterometry 4 4 2 2 2

Total Responses 45 36 25 22 31

Percent of Total 28 23 16 14 19

^ No entries in this portion of the survey.

Table 11. Use and Value of Optical Characterization Methods

Optical Method Critical Useful

Not Used Percent

Use

Value

Rating

Final

Rank

Optical microscopy 23 13 1 97 1.6 1 Ellipsometry 19 1

7 81 1.3 2

Infrared spectroscopy 20 8 7 80 1.4 2

Photoluminescence 10 9 14 58 0.9 3

Interferometry 9 7 14 53 0.8 4

Reflectometry 10 7 15 53 0.8 4

Scatterometry 8 9 15 53 0.8 4

Photoreflectance 4 1

17 47 0.6 5

Raman scattering 2 10 21 36 0.4 6

Total 105 85 1 1

Other Methods'

Photoconductive, photovoltaic 5 4

Miscellaneous^ 17 12

Added by respondents.

^ All other methods combined. Each method was cited by only one respondent as either

"critical" or "useful."

Note — The entries in the table represent a composite of usage on both silicon and compound

semiconductor materials and devices.

8
be applied to any of these areas, responses from the equipment manufacturers were not included

in the tally by material type.

The data reported here have not been analyzed as to which area the response originates.

Because the silicon and compound semiconductor fields differ significantly in terms of the

materials properties that must be controlled as well as in the mix between R&D and production

activity, this lack of differentiation may cause a further bias of the reported results.

Nevertheless, the results of the survey provide considerable insight into the requirements for and

usage of optical characterization methods in the semiconductor industry. This insight provides

useful guidance for the definition and prioritization of metrology development and

standardization programs.

USE AND VALUE OF THE METHODS

Table II summarizes the responses relating to the industrial use and value of various

optical characterization methods. Respondents were asked to rank each method as "critical"

(essential for the end application), "useful" (the method gives valuable but not essential

information), or "not used." In the table, the methods are listed in order of the extent of use, measured by the percentage of responses given as either critical or useful. The "value rating"

is determined by weighting the number of "critical" responses by 2, the number of "useful"

responses by 1, and the number of "not used" responses by 0, and dividing the weighted sum

by the total number of responses. The last column is the ranking of the impact of the techniques

based upon a combination of their value ratings and their percent use.

The method most widely used by respondents to the survey is optical microscopy and the

method reported to be least used is Raman scattering. Although scatterometry falls well down

on the list, it should be noted that this technique is the basis of scanning surface inspection

systems (laser surface scanners) which are universally used by silicon materials and device

manufacturers for automated particle counting. It should also be noted that reflectometry has

been widely utilized for a considerable time in silicon device production to measure the thickness

of thin films. More recently, ellipsometry is being explored as an in-situ method for controlling

depositions of thin films on silicon, but in-situ metrology is still not widely employed in the

industry.

In addition to the nine methods explicitly covered by the questionnaires, respondents were

asked to indicate any other optical techniques that they considered to be either critical or useful.

Nine respondents listed photovoltaic and photoconductive methods as either critical or useful.

Taken together, these methods appear to be less widely used than Raman scattering. Twentynine other optical characterization methods were listed as critical or useful by one of the

respondents.

9
PROPERTIES CHARACTERIZED

To determine what material properties are characterized by optical methods, 13 properties were explicitly listed in the survey. These properties were selected as those essential to characterize, design, and fabricate electronic and photonic devices. Table III summarizes the

materials properties reported to be measured optically by the respondents to the survey. This

table combines responses from both the silicon and compound semiconductor fields and from

all sectors of the research-to-product cycle.

Bold-face entries represent a significant intersection of methods and properties. For

instance, the responses to the survey show that ellipsometry is the most widely used method for

determining film properties, but infrared spectroscopy, interferometry, and reflectometry are also

utilized with some frequency. As discussed above, this result may arise from the biasing of the

responses toward the product development portion of the research-to-product cycle, since it is well known that reflectometry is most widely used for this measurement in the production

environment.

The last row of the table gives the number of listed materials properties reported to be

measured by each technique. Many optical methods are reported to be extremely versatile;

ellipsometry, infrared spectroscopy, photoluminescence, and Raman scattering are reported to be used for the measurement of 10 to 12 of the 13 listed material properties.

MEASURED MATERIALS AND DEVICES

Respondents to the questionnaire reported that they examine materials by optical methods

about three times as often as they do devices, including both devices in process and finished

devices. Table IV summarizes the relative usage of the listed optical characterization methods

for materials and device characterization. The method most widely used for characterizing

devices is microscopy, but even this technique was reported to be used more frequently for

materials characterization. All of the other listed methods were reported to be overwhelmingly

used for characterizing materials.

The table also indicates the type of material structures that were reported to be

characterized by optical methods. Respondents to the survey measure materials most often in

film form, with measurements on bulk materials a distant second. This no doubt reflects the fact

that ellipsometry and reflectometry are the two primary techniques for measuring film thickness.

Measurement of material microstructure (abbreviated "Micro" in the table) are most often made

on relatively exotic III-V and II-VI ternary and quaternary material systems for photonic devices.

Measurement of surfaces and interfaces appear to be made less frequently.

10
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Table IV. Relative Usage of Optical Characterization Methods on Materials and Devices

Optic6l Method

Materials Material Configuration Device

Use Bulk Film Micro Surface Use

Ellipsometry 26 8 29 8 10 9

Infrared Spectroscopy 25 12 20 6 1 4

Interferometry 12 4 1

1

1 3 4

Optical Microscopy 26 12 27 12 13 17

Photoluminescence 19 1

1

16 1

1

5 4

Photoreflectance 11 3 7 6 6 3

Raman Scattering 8 4 7 4 2 2

Reflectometry 12 3 7 4 5 5

Scatteronnetry 11 9 8 4 3

Other 31 28 17 8 3 8

Total 181 94 149 64 48 59

Table V indicates that the respondents to the survey use optical characterization methods

most often to measure silicon, closely followed by dielectrics and dielectric films, and Group

III-V semiconductors. Group II-VI semiconductors and metals are cited much less frequently

by the respondents to the survey. The citations for measurements on compound semiconductors

also include ternary and quaternary compounds for photonic devices. This distribution tends to

reflect the composition of the respondents to the survey as indicated in Table I as does the fact

that more work was not reported on diamond and no work was reported on either silicon carbide

or germanium-silicon alloys.

Table VI lists the electronic and photonic devices that were reported to be examined by

optical characterization methods for both electronic and photonic devices. As might be expected

from relative market sizes, photonic devices are characterized much less frequently than

electronic devices.

12
Table V. Materials Reported to be Characterized by Optical Methods

Material Number of Citations Category Totals

SILICON 65

Crystalline and polycrystalline Si 57

Amorphous Si 8

DIELECTRICS, DIELECTRIC FILMS 60

Unspecified 12

Si02, Si02/Si, SIMOX 29

SiN, 19

GROUP lll-V SEMICONDUCTORS 59

Unspecified 4

GaAs 1

1

AIGaAs, GaAs/AIGaAs systems 18

InGaAs/GaAs/AIGaAs systems 1

1

InGaAlP 7

InSb, InAISb, GaSb 6

AIN 2

GROUP ll-VI SEMICONDUCTORS 36

Unspecified 5

CdTe 6

CdTe/CdZnTe systems 5

HgCdTe, CdTe/HgCdTe systems 18

ZnS 2

METALS 15

Metal films, metals (unspecified) 8

Aluminum 2

Tin 1 Titanium, titanium nitride 3

Tungsten 1 OTHER GROUP IV SEMICONDUCTORS 1 Diamond 1 OTHER* 13

Composites, contaminants, fluids, glass. high-Tp superconductors, photoresist.

13
Table VI. Applications of Optical Characterization Techniques to Electronic and Photonic

Devices

Number of Number of

Electronic Devices Citations Photonic Devices Citations

Unspecified 15 Sources

Microprocessors, memory 11 Quantum-welllasers 10

Silicon linear and digital ICs 10 Electroluminescent devices 4

HEMT, p-HEMT 9 Light emitting diodes 1 CMOS, MOS capacitor 5 Detectors, Solar Cells

MESFET 4 Infrared, x-ray, unspecified 9

Magnetoresistors 2 Solar cells 1 Other

, Optical modulators 4

Flat panel displays 1

Total 56 Total 30

RANGE AND PRECISION

Table VII summarizes the range, precision, and spatial characteristics of the reported

optical measurement techniques. Empty boxes represent responses too limited, too scattered, or too ill-defined to tabulate. It proved difficult for the respondents to define all the details of

quantitative measurement in brief form, and that may be one reason why the number of

responses to the questions on these issues was not large. For some material properties, such as

carrier lifetime, the range of measured values is enormous. Such large ranges suggest the

diversity and flexibility of optical characterization methodology, but make it difficult to define

a single overall value for precision. In addition, the concept of measurement precision does not

apply to properties such as impurity type or defect type (for which the precision is indicated as not applicable, listed as "NA" in the table). Where a precision is given, it is the mean of the

reported values, rounded to single-digit resolution. A precision value is quoted only where the

database was relatively large and where the concept of precision appeared to be similarly defined

by different users. Despite these limitations, the reported values provide a rough estimate of

what optical methods can achieve.

Because optical characterization methods can be applied to a variety of sample sizes and

shapes, respondents were asked to specify the sample size they examined. In most cases, the

maximum area examined, listed in the third column of the table, was an entire 100 mm diameter

14
Table VII. Range and Precision of Measurements, and Maximum Sample Area Examined

Material Property —

Number of

Citations Range

Mean

Precision

Maximum

Area, cm'' Reset

Alloy Composition 1

1

0 to 1 00% 0.02 81

Carrier Density oo 1 0 to 10 cm 50%

uarrier ivioDiiity

1

1

Carrier Lifetime / 1 ps to 10s 10% Full wafer

v^rysLai ^oTieniaiion O

£. Full wafer

urystaiiinity A4 1 76

uetect Density 1 6 10 to 10 cm 314 100//m

r^pfpr^t T"\/np o M A o 1 1 /ym

Energy Band Gap 9 0 to 2 eV 0.03 eV 81

Film Thickness 24 2 nm to 50 //m 2% 625 30 //m

Impurity Density 9 176 2 mm

Impurity Type 8 NA

Resistivity 2

wafer or larger. This is not meant to imply that the beam covers this entire area; in many cases

the measured property is determined at many locations on the wafer surface to provide a map

of the distribution of the property value. This is particularly important in assessing the

uniformity of a crystal or of a deposited film.

The values in the last column of the table, labeled "Reset," relate to the reproducibility

of spatial positioning of the optical beam on a sample. These data are subject to even greater

limitations than the other table entries because they draw only on the responses to the expanded

version of the questionnaire. These entries should be taken as only as order-of-magnitude

estimates.

Whatever the absolute values of precision and the other attributes, it is essential that they

serve the needs of the industry. To address this issue, survey respondents were asked to answer "Yes" or "No" to the following questions: Is the measurement precision adequate to your

needs? Is the spatial resolution adequate? Is the accuracy of resetting to a given position on the

sample adequate? Are standards or test methods needed to conduct the measurement? Are such

standards or test methods available?

The responses are summarized in Table VIII. The first three columns of the table show

that on average, the precision, resolution, and ability to reset are thought to be adequate about

15
Table VIII. Degree of Respondents' Satisfaction with Selected Attributes of Optical Methods

for Characterizing Various Material Properties

Material Property

Precision

Adequate?

Spatial

Resolution

Adequate?

Reset Capability

Adequate? Standards

Needed?

Standards

Available?

I CO No Yes No Yp<? 1 CO Nn 1 CO Yp<; 1 Co Mn

Alloy Composition 10 1 10 1 7 3 3 3

Carrier Density 1 2 1 1 2 2

Carrier Mobility . 1 1 1

9 rri o r 1 if 0+ 1 mo 7 4 1 1 1 2 1 1 4

wrybLdl rx/ct" Q 1 VJllclHdLIUII ri 0 n+ at 1 0 n 1 1 1 1 2 2 1

Crystallinity 2 2 2 1 1 3 1 2

L^c^lcLfL L/t^llolLy 10 6 13 6 5 2 10 3 3 8

Defect Type 3 3 2 3 3 1 5 1 5

Energy Band Gap 9 7 1 4 3 2 2

Film Thickness 19 5 11 9 7 2 15 3 6 12

Innpurity Density 3 6 6 1 1 2 5 2 4

Impurity Type 2 6 1 5 2 6 1 7

Resistivity 1 1 1 1 1 2 2

Total 69 1 33 60 31 21 8 63 15 20 53

Percent 68 32 66 34 72 28 81 19 27 73

Table IX. Degree of Use and Satisfaction with Other Attributes of Optical Characterization

Techniques

Sensitivity Automatic Loading Data Communications Speed Pattern Recognition

Property Adequate? Adequate? Used? Adequate? A^^^"^^^' Used? Adequate?

Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No

Carrier Lifetime 1 0 2 1 1 1 1 1 0 2 0 1 Defect Density 3 2 6 1 5 1 5 2 3 3 2 2 2 3 2 2 Defect Type 1 1 2 1 2 1 3 0 2 1 1 2 1 2 1 1

Film Thickness 6 2 7 2 5 2 7 3 4 3 4 3 3 4 1 2

Impurity Density 1 2 1 2 1 1 3 1 2 1 2 1 0 1 0 1

Impurity Type 1 1 0 1 0 1 1 0 1 0

Resistivity 1 0 1 0 0 1 0 1 1 2 1 3 1 2

Total 13 7 18 8 15 6 20 8 13 10 1 1 12 7 13 5 9 Percent 65 35 69 31 71 29 71 29 56 44 48 52 35 65 36 64

16
70% of the time. However, there are wide variations in the responses for individual parameters.

For instance, there is a high degree of satisfaction in the measurement of alloy composition, but concern about determination of impurity type. Regardless of the degree of satisfaction, the next

column shows strong agreement with the proposition that standards and test methods are needed.

By contrast, the last column shows nearly equally strong agreement that these are not now

available. This expressed need for optical measurement standards is one of the important

findings of the survey, clearly pointing to an area where NIST can contribute.

The expanded version of the survey requested further information about the measurement

process. Table IX summarizes the responses to questions regarding the adequacy of the lower

detection limit of measurement (measurement sensitivity), use and adequacy of automatic cassette loading of the measurement instrument (auto transport), use and adequacy of the ability to capture data and print it or send it to a host computer or storage medium (data communications),

adequacy of the speed of the measurement system (speed), and use and adequacy of pattern

recognition techniques (pattern recognition). The data in the table are from the responses to the

expanded version of the questionnaire, and so there were a relatively small number of responses.

Omitted parameters had no responses.

Two-thirds of the respondents were satisfied with the sensitivity of the measurement

methods. Large fractions of the respondents use, and are satisfied with, automatic cassette loading of samples. Many capture the characterization data for further analysis by computer,

but nearly half find this aspect unsatisfactory. More than half the users consider the speed of

measurement to be inadequate. About one-third of the respondents use pattern recognition

techniques, and two-thirds find these unsatisfactory. Although these data represent a very small

sampling, they provide some indication of the degree of satisfaction and usage of these attributes

of optical characterization techniques.

COMPARISON TO OTHER METHODS

Respondents were asked to identify reasons why they would prefer to utilize optical

characterization techniques in preference to some other type of measurement method for a

particular material property. Table X summarizes the responses to this question for a variety

of material properties.

Entries in the second column of the table indicate the number of times that respondents

stated that other nonoptical methods could be used to determine the same information. Each of

the other columns represent a reason why the optical rather than the nonoptical method is used:

higher speed or greater throughput of the optical method (speed), higher accuracy attainable with

the optical method (acc), the nondestructive nature of the optical measurement (NDE), the

reduced preparation effort required to make the optical measurement (prep), higher spatial

17
I

I

Table X. Reasons for Selection of Optical Methods over Other (Non-Optical) Techniques to

Measure a Given Material Property

Material Property

NonOptical

Method

Available

Speed Acc NDE Prep Res Cost Area

Alloy Composition 15 10 3 10 6 2 4 7

Carrier Density 5 4 2 1 1 2

Carrier Mobility 4 1 2 1 1 2

Carrier Lifetime 4 3 1 4 2 1 2

Crystal Orientation 3 1 1

Crystallinity 10 6 2 5 2 3 4

Defect Density 15 12 2 10 7 1 4 5

Defect Type 1

1

8 6 4 1 3 1 Energy Band Gap 7 6 4 6 3 2 2 4

Film Thickness 25 16 7 22 16 4 4 8

Impurity Density 12 7 1 10 7 2 4 4

Impurity Type 14 9 2 9 7 2 3 4

Resistivity 2 1 1 1

Total 127 82 22 88 57 17 27 45

Table XI. Reasons That Optical Characterization Methods Are Not Used

Method Cost Equipment Support Sensitivity Precision Standards Other

Ellipsometry 4 2 3 1 1

Infrared Spectroscopy 1 Interferometry 1 2 2

Optical Microscopy 1 1 1 Photoluminescence 1 2 3 1 1 Photoreflectance 1 1 1 2

Raman Scattering 5 1 5 2 3

Reflectometry 2 3 3 4

Scatterometry 1 1 4 3

Total 15 10 21 1 2 4 17

18
Table XII. Source of Optical Characterization Equipment Used in the Semiconductor Industry

Optical Characterization Method Commercial Equipment Equipment Built In-House

Ellipsometry 23 4

Infrared Spectroscopy 24 1 Interferometry 10 3

Optical Microscopy 31 2

Photoluminescence 7 9

Photoreflectance 5 0

Raman Scattering 4 0

Reflectometry 10 2

Scatterometry 9 4

Other 15 12

Total 138 47

Percent of Total 75 25

Table Xill. Costs Associated with the Use of Optical Characterization Equipment in the

Semiconductor Industry

Optical Characterization

Method

Cost

($1,000)

Operation

($1,000/year)

Staff

(FTE)

Ellipsometry 97 (9 to 375) 4 (0 to 20) 0.5 (0 to 1.5)

Infrared spectroscopy 94 (20 to 300) 15 (0.5 to 85) 0.6 (0.1 to 2)

Interferometry 82 (2 to 300) 4 (0 to 16) 0.6 (0.1 to 1)

Optical microscopy 70 (3 to 1,000) 7 (0 to 80) 0.9 (0 to 10)

Photoluminescence 52 (15 to 150) 7 (0 to 20) 0.5 (0.2 to 1)

Photoreflectance 43 (10 to 150) 3 (0 to 10) 0.5 (0.1 to 1)

Raman scattering 96 (30 to 150) 8 (0 to 20) 0.5 (0.2 to 1)

Reflectometry 75 (10 to 320) 2 (0 to 10) 0.6 (0.1 to 2)

Scatterometry 1 17 (25 to 350) 5 (0 to 35) 0.7 (0.1 to 2)

Other 87 (8 to 250) 11 (0 to 80) 0.8 (0.1 to 2)

19
resolution of the optical method (res), the lower cost of the optical method (cost), and the

capability of the optical method to measure over an extended area (area). The nondestructive

nature and high speed of optical techniques were cited as the most important reasons for

preferring these methods over others. Reasons cited less frequently included the reduced

preparation effort required and the ability to examine different portions of a sample.

Respondents were also asked to indicate reasons why they do not employ optical

techniques that they would expect to find useful for characterizing materials or devices. Table

XI summarizes the small number of responses to this question. Lack of technical support,

presumably either by the instrument manufacturer or from an in-house support group, was cited

most frequently as the reason that potentially useful optical methods are not employed. Cost and

lack of commercial equipment were listed as the next most important considerations. The

importance of the availability of commercial equipment was indicated by the fact that three out

of four applications reported by survey respondents utilized commercially available equipment,

as shown in Table XII.

The capital, operational, and staff investments necessary to carry out optical

characterization as reported by the respondents to the survey are summarized in Table XIII. Equipment costs vary greatly, in some cases by a factor of more than 10. This may reflect the

presence of multiple measurement stations, in-house vs. commercial costs, and the degree of

automation. For example, as noted previously, three out of four applications involve the use of

commercially available apparatus, although in the several areas where there is a significant usage

of in-house equipment, the reported equipment costs tended to be somewhat lower.

COST ISSUES

Operational costs also vary widely, probably for similar reasons, and because different

organizations may allocate such costs differently. Some of the diversity in the staff numbers

may also reflect how staff time is allocated for internal budgeting, as well as the number of

stations. Despite the wide variation in both equipment and operating costs reported by the

respondents to the survey, cost is perceived as a major inhibiting factor to the use of optical

characterization methods by many in the industry.

COMMENTS FROM RESPONDENTS

In addition to responding to fixed questions, respondents were asked for their free-form

comments in four areas: optical characterization methods not previously mentioned that the

respondent would find useful for future applications, ways in which NIST could help to improve

optical characterization methods, application of optical characterization techniques to non- semiconductor materials, and any other important issues not covered by the questions in the

20
survey form. Comments on the first, second, and fourth of these issues were received from a very small fraction of the total number of respondents. Many respondents had identified in their

responses to earlier questions in the survey that they measure nonsemiconductor materials

associated with device strucmres, such as dielectric and metal films, with the use of optical

characterization techniques.

Half a dozen respondents mentioned spectroscopic ellipsometry as well worth further

development. Two would like to see development of photoluminescence, one suggesting a need

for a packaged system that could operate over the temperature range from 10 K to 400 K. For

both techniques, cost was mentioned as a barrier to future use.

The biggest issue raised concerning NIST involvement was related to developing

reference materials for optical characterization. This was mentioned in nearly two-thirds of the

responses made in essay form. Examples where such reference materials might be most useful

include film thickness standards for Si02/Si and multilayer films 2 nm to 10 nm thick, standards

for defects and surface microroughness in silicon, and standards for spectroscopic ellipsometry.

Requests were also made for standardized measurement procedures and analytical software, a

catalog of photoluminescent spectral signatures from impurities, and workshops.

Some respondents were concerned about the lack of fundamental work in the physics of

characterization. Most instrument manufacturers were thought to be too small to carry out such

research, and university work in this area was perceived as limited in scope. The database for

optical characterization activities was seen as lacking, for instance in energy gap v^. alloy

content for AlGaAs and InGaAs. Some respondents looked to NIST to establish such data. Two

respondents consider in-situ measurement and optically-guided control of sample growth as important future possibilities not treated in the survey. One felt that despite the obvious

advantages of optical characterization as a nondestructive technique, its benefits and drawbacks

have yet to be clearly laid out to the industry.

SUMMARY

Optical methods are used to characterize a wide variety of material systems. The 42

responses from different types of firms show that these techniques are heavily used in industrial

research and development activities. Of the specific techniques identified, microscopy has had

the greatest impact, and Raman scattering, the least. The nondestructive nature of optical

methods is a major reason both for their present use and for their future importance for in-situ

characterization. Lack of technical support is the main reason given for not employing optical

techniques.

21
The respondents' largest single application of optical techniques is to silicon, but optical

characterization of dielectrics and dielectric films and Group III-V semiconductors is nearly as widespread. A diverse set of devices is examined by these techniques. Among the respondents

to the survey, electronic devices are examined by optical characterization methods twice as often

as photonic ones.

The range of values that can be measured for many properties is broad, and precision

ranges from moderate to excellent. Precision, sensitivity, and spatial resolution are thought

adequate for two out of every three current applications, but deficiencies were noted in some

specific areas. Ellipsometry and infrared spectroscopy are reported to be the most expensive

methods; photoluminescence and photoreflectance, the least expensive. Many users carry out

optical characterization with a relatively modest investment, but the reported range of costs

involved was very large.

The need for reference materials and standard test methods for optical techniques is an

important finding of the survey. A number of respondents would find workshops on these

techniques to be useful.

ACKNOWLEDGMENTS

The authors gratefully aclcnowledge E. Jane Walters of the Semiconductor Electronics Division

whose expert assistance enabled this survey of the semiconductor industry to be successfully

accomplished.

REFERENCES

[1] S. Perkowitz, D. G. Seiler, and W. M. Bullis, "Optical Characterization of Materials and

Devices for the Semiconductor Industry: Trends and Needs," Semiconductor

Characterization: Present Status and Future Needs, W. M. Bullis, D. G. Seiler, and A.

C. Diebold, eds. (AIP Press, Woodbury, NY, 1995), pp. 422-427.

[2] Proceedings of the International Workshop in Process Control Measurements for

Advanced IC Manufacturing, November 9-10, 1992, Austin, Texas, P. H. Langer and

W. M. Bullis, eds. (Semiconductor Equipment and Materials International, Mountain

View, California, 1993), pp. 5, 13.

[3] S. Perkowitz, D. G. Seiler, and W. M. Duncan, "Optical Characterization in

Microelectronics Manufacturing," J. Res. Natl. Inst. Stand. Technol. 99 (5), 605-639

(1994).

[4] S. Perkowitz, Optical Characterization of Semiconductors: Infrared, Raman, and

Photoluminescence Spectroscopy (Academic Press, London, 1993).

[5] H. G. Tompkins, A User's Guide to Ellipsometry (Academic Press, Inc., San Diego,

1993).

22
R. M. A. Azzam and N. M. Bashara, Ellipsometry and Polarized Light (North Holland,

New York, 1989).

J. R. Ferraro and K. Krishnan, Practical Fourier Transform Infrared Spectroscopy:

Industrial and Laboratory Chemical Analysis (Academic Press, San Diego, 1990).

W. M. Bullis, "Oxygen Concentration Measurement," in Oxygen in Silicon, F. Shimura,

ed. (Academic Press, Inc., Boston, 1994), Chapter 4.

N. Bobroff, "Recent Advances in Displacement Measuring Interferometry," Measurement

Science and Technology 4, 907-926 (1993).

D. E. Aspnes, "Modulation Spectroscopy/Electric Field Effects on the Dielectric Function

of Semiconductors," Handbook on Semiconductors, Vol. 2, T. S. Moss and M. Balkanski,

eds. (North Holland, New York, 1980), p. 109.

See, for example, the section on Optica) Microscopy in Reference [3], pp. 617-623.

M. Tajima, "Quantitative Impurity Analysis in Si by the Photoluminescence Technique,"

in Japan Annual Reviews in Electronics, Computers, and Telecommunications - Semiconductor Technology, J. Nishizawa, ed. (OHM-North Holland, 1982).

J. G. Grasselli and B. J. Bulkin, eds.. Analytical Raman Spectroscopy (Wiley, New York,

1990).

J. C. Stover, Optical Scattering: Measurement and Analysis, 2nd Edition (SPIE Optical

Engineering Press, Bellingham, Washington, 1995).

23

Appendix A

Initial Survey Form

25

NIST form # (unnumbered)

OMB Approval # 0693-0014

Expiration Date: 06/30/93

Public reporting burden for this collection of information is estimated to average one hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the

collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,

including suggestions for reducing this burden, to Dr. David G. Seiler, Semiconductor Electronics Division, National Institute of

Standards and Technology, Gaithersburg, MD 20899, and to the Office of Management and Budget, Paperwork Reduction Project

(OMB # 0693-0014), Washington, DC 20503. NOTE: DO NOT SEND COMPLETED FORM TO OMB. USE ADDRESS

SHOWN ON PAGE 8.

OPTICAL CHARACTERIZATION METHODS FOR MATERL\LS, PROCESSING,

AND MANUFACTURING IN THE SEMICONDUCTOR INDUSTRY

QUESTIONNAIRE FOR INDUSTRL\L USERS OF OPTICAL CHARACTERIZATION METHODS

(1) Check the appropriate column below to show whether you use any of the listed optical methods to characterize,

diagnose, or help in processing either: (a) semiconductors or semiconductor substrates for electronic, photonic, or other devices; (b) the devices themselves. "Critical" means the optical method is essential for your end application;

"useful" means the method gives valuable but not essential information.

Critical Useful Don't use

Ellipsometry

Infrared spectroscopy (e.g., FTIR)

Interferometry

Optical microscopy (visible or infrared)

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other methods (indicate)*

*Add any other techniques you use such as: time-resolved, synchrotron, free-electron laser, photothermal,

photoacoustic, laser-beam-induced current, optical-beam-induced reflectance, nonlinear spectroscopy, attenuated total reflectance, reflectance-difference, photo-injection, photoconductive, photovoltaic.
(2) For each critical or useful method checked in Question 1, indicate below in the material/device column whether

it is used on a material, or on a device. If the former, identify the material (for example, high-resistivity Si, or AlGaAs), and the end device which uses it. If a device, identify it (for example, light-emitting diode) and the material

of which it is made. In all cases, check whether the material involved is in bulk, film, or microstructure form (any

multiple layer structure such as a heterostructure, superlattice, or multiple quantum well), abbreviated "micro."

Material Surface/ or device? Material Bulk Film Micro Interface Device

Ellipsometry

Infrared spectroscopy

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

* Identify

2
(3) For each critical or useful method you checked in Question 1, indicate below what material or device parameter

it measures, by a check at the appropriate junction of method (listed horizontally) and parameter (Usted vertically).

The methods in Question 1 are abbreviated as ELL, eUipsometry; IR, infrared; IN, interferometry; MIC, microscopy;

PL, photoluminescence; PR, photoreflectance; RAM, Raman; REF, reflectometry; SC, scatterometry; other.

METHODS

PARAMETERS ELL IR IN MIC PL PR RAM REF SC OTHER* OTHER*

Alloy composition _____

Carrier density

Carrier mobility

Carrier Ufetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

*Identify

3
(4) For each parameter you checked in Question 3, give the range of values measured, and the precision or uncertainty

achieved (if you do a statistical analysis, please use a single standard deviation) of the measurement as a ± percent

of the quantity measured, and indicate if this is adequate (yes or no). If the parameter is measured over a spatial extent (example: to produce a map of defect density over a siUcon wafer), in the "spatial" column, state the total size of the area you examined, the spatial resolution used, and whether this resolution is adequate. Also indicate if the

measurement requires physical standards or test methods, and what types (such as wavelength, intensity, or thickness

standards), and if adequate standards or test methods are available.

Range Precision Adequate Spatial Adequate Standards/ Adequate

Test Methods

Alloy composition

Carrier density

Carrier mobility

Carrier hfetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Fibn thickness

Impurity density

Impurity type

Resistivity

Other*

•Identify

If you have indicated that inadequacies exist for these measurements, please comment on their nature and significance

and what is needed in Question 9 or 10. Including an estimate of the cost to your company arising from the

inadequacies you have identified would be helpful.

4
(5) For each parameter you checked in Question 3, check the "yes" column below if the same information can be

obtained by non-optical methods. For each "yes" answer, check the reason(s) why you chose the optical rather than

the non-optical method, abbreviated as follows: SPD —higher speed or greater throughput; ACC —higher accuracy;

NDE — nondestructive nature of optical measurement; PRE — reduced preparation effort; HSR — high spatial

resolution needed; COS — lower cost; SPA — capabiUty to measure over a spatial extent; other.

YES SPD ACC NDE PRE HSR COS SPA OTHER* OTHER*

Alloy composition

Carrier density

Carrier mobility

Carrier lifetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

* Identify
(6) For each critical or useful method in Question 1, check whether you use commercial equipment, or a faciUty

designed or built in-house. Give the approximate cost to buy or build the equipment; yearly operating cost, including

maintenance, and supplies such as cryogens; and the number of full-time equivalent (FTE) people needed to run the

facility, obtain data, and interpret data. Yearly

Equipment Equipment Operating FTE

Commercial In-house cost cost people

EUipsometry

Infrared

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

* Identify

(7) Consider any methods in Question 1 which you do not currently use, but which could be helpful. For each, check

the reason(s) you do not use it: cost of instaUing and/or operating; lack of commercial equipment; lack of technical

support for the equipment or the data analysis; inadequate sensitivity; inadequate precision; inadequate physical

standards or test methods; other.

Lack of Lack of Inadequate

commercial technical Inadequate Inadequate Standards/

Cost equipment support sensitivity precision Test Methods Other*

EUipsometry

Infrared

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

* Identify

6
(8) Please list and briefly describe any optical methods you have not yet mentioned which might develop value for meeting your future characterization needs.

(9) Please add any comments you wish to make about the use of optical characterization for your appUcations.

Identification of what you consider to be the important issues, especially any not addressed by this questionnaire, is welcome.

(10) In what specific ways could NIST help you to improve your optical characterization methods?
(11) What non-semiconductor materials are also characterized by optical methods in your work? Please Ust the

materials and the optical method used.

Please return this Questionnaire to the following address:

Dr. David G. Seller National Institute of Standards and Technology

Semiconductor Electronics Division

Bldg. 225, Room A305

Gaithersburg, MD 20899

Telephone: 301-975-2074

FAX: 301-948-4081

If you would like to receive a copy of the final report, please write your name and address below. If you would be

wiUing to receive a telephone call regarding questions about your response, please include your telephone number.

Providing this information in no way will compromise our promise of confidentiahty.

Name

Telephone

8
Appendix B

Expanded Survey Form

35

NIST form # (unnumbered)

0MB Approval # 0693-0014

Expiration Date: 12/31/93

Public reporting burden for this collection of information is estimated to average one hour per response, including the time for reviewing

instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of

information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Dr. David G. Seller, Semiconductor Electronics Division, National Institute of Standards and Technology,

Gaithersburg, MD 20899, and to the Office of Management and Budget, Paperwork Reduction Project (0MB # 0693-0014), Washington,

DC 20503. NOTE: DO NOT SEND COMPLETED FORM TO 0MB. USE ADDRESS SHOWN ON PAGE 8.

OPTICAL CHARACTERIZATION METHODS FOR MATERIALS, PROCESSING,

AND MANUFACTURING IN THE SEMICOr^UCTOR INDUSTRY

QUESTIONNAIRE FOR INDUSTRIAL USERS OF OPTICAL CHARACTERIZATION METHODS

(1) Check the appropriate column below to show whether you use any of the listed optical characterization methods: (a) as a materials supplier of semiconductors or semiconductor substrates for electronic, photonic, or other devices; (b) as a manufacturer of the devices themselves; or (c) as an equipment supplier. In all cases, please insert the appropriate letters

(a), (b), or (c) in the "Critical" and "Useful" columns. "Critical" means the optical method is essential for your end

application; "useful" means the method gives valuable but not essential information.

Type of Use

R&D Process Off-Line Quality Process Critical Useful Don't use

Devel. Diagnos. Control Control

Ellipsometry

Infrared spectroscopy

(e.g., FTIR)

Interferometry

Optical microscopy

(visible or infrared)

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other methods

(indicate)*

*Add any other techniques you use such as: time-resolved, synchrotron, free-electron laser, photothermal, photoacoustic,

laser-beam-induced current, optical-beam-induced reflectance, nonlinear spectroscopy, attenuated total reflectance,

reflectance-difference, photo-injection, photoconductive, photovoltaic.
(2) For each critical or useful method checked in Question 1 , indicate below in the material/device column whether it is used on a material, or on a device. If the former, identify the material (for example, high-resistivity Si, or AlGaAs), and the end

device which uses it. If a device, identify it (for example, light-emitting diode) and the material of which it is made. In

all cases, check whether the material involved is in bulk, film, or microstructure form (any multiple layer structure such as a heterostructure, superlattice, or multiple quanmm well), abbreviated "micro."

Material Surface/ or device? Material Bulk Film Micro Interface Device

EUipsometry

Infrared spectroscopy

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

Identify
(3) For each critical or useful method you checked in Question 1, indicate below what material or device parameter it measures, by a check at the appropriate junction of method (listed horizontally) and parameter (listed vertically). The methods

in Question 1 are abbreviated as ELL, ellipsometry; IR, infrared; IN, interferometry; MIC, microscopy; PL,

photoluminescence; PR, photoreflectance; RAM, Raman; REF, reflectometry; SC, scatterometry; other.

METHODS

PARAMETERS ELL IR IN MIC PL PR RAM REF SC OTHER* OTHER*

Alloy composition

Carrier density

Carrier mobility

Carrier lifetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

Identify

3
(4a) For each parameter you checked in Question 3, give the range of values measured, and the precision or uncertainty

achieved (if you do a statistical analysis, please use a single standard deviation) of the measurement as a + percent of the quantity measured, and indicate if this is adequate (yes or no). If the parameter is measured over a spatial extent (example:

to produce a map of defect density over a silicon wafer), in the "spatial" column, state the total size of the area you

examined, the spatial resolution used, and whether this resolution is adequate. Also indicate if the measurement requires

physical standards or test methods, and what types (such as wavelength, intensity, or thickness standards), and if adequate

standards or test methods are available.

Range Precision Adequate Spatial Adequate Standards/ Adequate

Area Resolution Test Methods

Alloy composition

Carrier density

Carrier mobility

Carrier lifetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

Identify

If you have indicated that inadequacies exist for these measurements, please comment on their nature and significance and

what is needed in Question 9 or 10. Including an estimate of the cost to your company arising from the inadequacies you

have identified would be helpful.

4a
(4b) For each parameter you checked in Question 3, please provide these further details. Sensitivity refers to the lower detection

limit; auto transport, to the availability of automatic cassette loading of the instrument; communications, to the ability to capture data and either print it out or send it to a host computer or to storage media; positioning, to the ability to come back to the same location on the sample; pattern recognition, to the issue of finding a location within a pattern which contains a test element, defect, or other

structure which can be examined by the measurement method.

Measurement Sensitivity Auto Communications Positioning Pattern Speed Transport Recognition

Value Adequate Value Adequate Used Adequate Used Adequate Value Adequate Used Adequate

Alloy composition

Carrier density

Carrier mobility

Carrier lifetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

Identify

If you have indicated that inadequacies exist for these measurements, please comment on their nature and significance and what is needed in Question 9 or 10. Including an estimate of the cost to your company arising from the inadequacies you have identified would be helpful.

4b
(5) For each parameter you checked in Question 3, check the "yes" column below if the same information can be obtained by

non-optical methods. For each "yes" answer, check the reason(s) why you chose the optical rather than the non-optical method,

abbreviated as follows: SPD — higher speed or greater throughput; ACC — higher accuracy; NDE — nondestructive nature of

optical measurement; PRE — reduced preparation effort; HSR — high spatial resolution needed; COS — lower cost; SPA —

capability to measure over a spatial extent; other.

YES SPD ACC NDE PRE HSR COS SPA OTHER* OTHER*

Alloy composition

Carrier density

Carrier mobility

Carrier lifetime

Crystal orientation

Crystallinity

Defect density

Defect type

Energy band gap

Film thickness

Impurity density

Impurity type

Resistivity

Other*

*Identify

5
(6) For each critical or useful method in Question 1, check whether you use commercial equipment, or a facility designed or built in-house. Give the approximate cost to buy or build the equipment; yearly operating cost, including maintenance, and supplies such

as cryogens; and the number of full-time equivalent (FTE) people needed to run the facility, obtain data, and interpret data. Yearly

Equipment Equipment Operating FTE

Commercial In-house cost cost people

Ellipsometry

Infrared

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

Identify

(7) Consider any methods in Question 1 which you do not currently use, but which could be helpful. For each, check the reason(s)

you do not use it: cost of installing and/or operating; lack of commercial equipment; lack of technical support for the equipment or

the data analysis; inadequate sensitivity; inadequate precision; inadequate physical standards or test methods; other.

Lack of Lack of Inadequate

commercial technical Inadequate Inadequate Standards/ Cost equipment support sensitivity precision Test Methods Other*

Ellipsometry

Infrared

Interferometry

Optical microscopy

Photoluminescence

Photoreflectance

Raman scattering

Reflectometry

Scatterometry

Other*

* Identify

6
(8) Please list and briefly describe any optical methods you have not yet mentioned which might develop value for meeting your future characterization needs.

(9) Please add any comments you wish to make about the use of optical characterization for your applications. Identification of what

you consider to be the important issues, especially any not addressed by this questionnaire, is welcome.

(10) In what specific ways could NIST help you to improve your optical characterization methods?
(11) What non-semiconductor materials are also characterized by optical methods in your work? Please list the materials and the

optical method used.

Please return this Questionnaire to the following address:

Dr. David G. Seiler National Institute of Standards and Technology

Semiconductor Electronics Division

Bldg. 225, Room A305

Gaithersburg, MD 20899

Telephone: 301-975-2074

FAX: 301-948-4081

If you would like to receive a copy of the fmal report, please write your name and address bdow. If you would be willing to receive

a telephone call regarding questions about your response, please include your telephone number. Providing this information in no way will compromise our promise of confidentiality.

Name

Telephone

8

Appendix C

Bibliography

47

Book Length Reviews and Compendia

C. R. Brundle, C. A. Evans, and S. Wilson, eds., Encyclopedia of Materials Characterization

(Butterworth-Heinemann, Boston, 1992).

W. M. Bullis, D. G. Seller, and A. C. Diebold, eds.. Semiconductor Characterization: Present

Status and Future Needs (AIP Press, Woodbury, New York, 1995).

J. R. Ferraro and K. Krishnan, eds., Practical Fourier Transform Infrared Spectroscopy

(Academic Press, San Diego, 1990).

J. G. Grasselli and B. J. Bulkin, eds.. Analytical Raman Spectroscopy (Wiley, New York, 1990).

S. Perkowitz, Optical Characterization of Semiconductors: Infrared, Raman, and

Photoluminescence Spectroscopy (Academic Press, London, 1993).

D. G. Seller and C. L. Littler, eds.. The Spectroscopy ofSemiconductors, in Semiconductors and

Semimetals (Academic Press, Inc., New York, 1992), Vol. 36.

Chapter Length Overviews/Review Articles

P. M. Amirtharaj and D. G. Seller, "Optical Properties of Semiconductors" in Handbook of

Optics, Vol. II, 2nd Edition, M. Bass, E. W. Van Strylarid, D. R. Williams, and W. L. Wolfe,

eds. (McGraw-Hill, New York, 1995), Chapter 36.

W. M. Bullis, "Oxygen Concentration Measurement" in Oxygen in Silicon, F. Shimura, ed.

(Academic Press, Inc. Boston, 1994), Chapter 4.

T. H. DiStefano, "Scanned Photovoltage and Photoemission" in Nondestructive Evaluation of

Semiconductor Materials and Devices, J. N. Zemel, ed. (Plenum, New York, 1979), Chapter 9.

P. F. Kane and G. B. Larrabee, Characterization ofSemiconductor Materials (McGraw-Hill, New

York, 1970).

E. C. Lightowlers, "Photoluminescence Characterisation" in Growth and Characterisation of

Semiconductors, R. A. Stradling and P. C. Klipstein, eds. (Adam Hilger, Bristol, 1990), pp. 135-

163.

R. C. Newman, "Localised Vibrational Mode Spectroscopy of Impurities in Semiconductor

Crystals," in Growth and Characterisation ofSemiconductors, R. A. Stradling and P. C. Klipstein,

eds. (Adam Hilger, Bristol, 1990), pp. 105-117.

E. D. Palik and R. T. Holm, "Optical Characterization of Semiconductors" in Nondestructive

Evaluation ofSemiconductor Materials and Devices, J. N. Zemel, ed. (Plenum, New York, 1979),

Chapter 7.

49
S. Perkowitz, D. G. Seller, and W. M. Duncan, "Optical Characterization in Microelectronics

Manufacturing," J. Res. Natl. Inst. Stand. Technol 99, 605-639 (1994).

D. K. Schroder, "Optical Characterization" in Semiconductor Material and Device Characterization (John Wiley & Sons, New York, 1990), Chapter 9.

Proceedings

R. A. Alfano, ed., Ultrafast Lasers Probe Phenomena in Bulk and Microstructure

Semiconductors, Proc. SPIE 793 (SPIE, Bellingham, 1987).

R. A. Alfano, ed., Ultrafast Lasers Probe Phenomena in Bulk and Microstructure Semiconductors

II, Proc. SPIE 942 (SPIE, Bellingham, 1988).

D. E. Aspnes, S. So, and R. F. Potter, eds., Optical Characterization Techniques for

Semiconductor Technology, Proc. SPIE 276 (SPIE, Bellingham, 1981).

J. W. Baars and R. E. Longshore, eds.. Future Infrared Detector Materials, Proc. SPIE 1106

(SPIE, Bellingham, 1989).

J. L. Benton, G. N. Maracas, and P. Rai-Choudhury, eds.. Diagnostic Techniques for

Semiconductor Materials and Devices, Proceedings Volume 92-2 (The Electrochemical Society,

Pennington, NJ, 1992).

L. J. Brillson and F. H. Pollak, eds.. Surface and Interface Analysis ofMicroelectronic Materials

Processing and Growth, Proc. SPIE 1186 (SPIE, Bellingham, 1989).

N. Cheung and M.-A. Nicolet, eds.. Materials Characterization, MRS Symposia Proceedings

Volume 69 (Materials Research Society, Pittsburgh, 1986).

O. J. Glembocki, F. H. Pollak, and F. Ponce, eds., Spectroscopic Characterization Techniques

for Semiconductor Technology III, Proc. SPIE 946 (SPIE, Bellingham, 1988).

O. J. Glembocki, J. J. Song, and F. H. Pollak, eds., Modern Optical Characterization Techniques

for Semiconductors and Semiconductor Devices, Proc. SPIE 794 (SPIE, Bellingham, 1987).

O. J. Glembocki, S. W. Pang, F. H. Pollak, G. M. Crean, and G. Larrabee, eds.. Diagnostic

Techniques for Semiconductor Materials Processing, MRS Symposia Proceedings Volume 324

(Materials Research Society, Pittsburgh, 1994).

D. C. Gupta, ed., Silicon Processing, ASTM STP 804 (American Society for Testing and

Materials, Philadelphia, 1983).

D. C. Gupta, ed.. Semiconductor Processing, ASTM STP 850 (American Society for Testing and

Materials, Philadelphia, 1984).

50
D. C. Gupta and P. L. Langer, eds., Emerging Semiconductor Technology, ASTM STP 960

(American Society for Testing and Materials, Philadelphia, 1987).

D. C. Gupta, ed., Semiconductor Fabrication—Technology and Metrology, ASTM STP 990

(American Society for Testing and Materials, Philadelphia, 1989).

J. R. Izatt, ed., Far-Infrared Science and Technology, Proc. SPIE 666 (SPIE, Bellingham, 1986).

B. J. Kolbesen, D. V. McCaughan, and W. Vandervorst, eds.. Analytical Techniques for

Semiconductor Materials and Process Characterization, Proceedings Volume 90-11 (The

Electrochemical Society, Pennington, NJ, 1990).

P. H. Langer and W. M. Bullis, eds.. Proceedings of the International Workshop on Process

Control Measurements for Advanced IC Manufacturing, Austin, Texas, November 9-10, 1992

(SEMI, Mountain View, 1992).

E. Passaglia. R. R. Stromberg, and J. Krueger, eds., Ellipsometry in the Measurement ofSurfaces

and Thin Films, NBS Misc. Publ. 256 (1964).

F. H. Pollak and R. S. Bauer, eds., Spectroscopic Characterization Techniquesfor Semiconductor

Technology I Proc. SPIE 452 (SPIE, Bellingham, 1983).

F. H. Pollak, ed. Spectroscopic Characterization Techniques for Semiconductor Technology II, Proc. SPIE 524 (SPIE, Bellingham, 1985).

T. J. Schaffner and D. K. Schroder, eds.. Diagnostic Techniquesfor Semiconductor Materials and

Devices, Proceedings Volume 88-20 (The Electrochemical Society, Pennington, NJ, 1988).

D. K. Schroder, J. L. Benton, and P. Rai-Choudhury, eds.. Diagnostic Techniques for

Semiconductor Materials and Devices, Proceedings Volume 94-33 (The Electrochemical Society,

Pennington, NJ, 1994).

R. D. Westbrook, Lifetime Factors in Silicon, ASTM Special Publication 712 (American Society

for Testing and Materials, Philadelphia, 1980).

51

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