Ellipsometry -- Principles

This document specifies a method for determining optical and dielectric constants in the UV-VIS-NIR spectral range as well as layer thicknesses in the field of at-line production control, quality assurance and material development through accredited test laboratories. It is applicable to stand-alone measuring systems. The presentation of the uncertainty of results conforms to ISO/IEC Guide 98-3.

Ellipsométrie -- Principes

General Information

Status
Published
Publication Date
21-Apr-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
27-Feb-2021
Completion Date
26-Feb-2021
Ref Project

Buy Standard

Standard
ISO 23131:2021 - Ellipsometry -- Principles
English language
15 pages
sale 15% off
Preview
sale 15% off
Preview
Draft
ISO/FDIS 23131:Version 26-dec-2020 - Ellipsometry -- Principles
English language
15 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 23131
First edition
2021-04
Ellipsometry — Principles
Ellipsométrie — Principes
Reference number
ISO 23131:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 23131:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 23131:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions, symbols and abbreviated terms ....................................................................................................... 1

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Symbols and abbreviated terms............................................................................................................................................... 1

4 Experimental boundary conditions with respect to the sample ........................................................................ 2

5 Experimental boundary conditions with respect to the measurement ......................................................3

6 Model-correlated boundary conditions of the simulation........................................................................................ 4

7 Basic models ............................................................................................................................................................................................................. 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Bulk material (case 1 of application) ................................................................................................................................... 5

7.3 Transparent single layer (case 2 of application) ....................................................................................................... 5

7.4 Semi-transparent single layer (case 3 of application) .......................................................................................... 5

7.5 Multiple layers and periodic layers (case 4 of application) ............................................................................. 5

7.6 Effective materials (case 5 of application) ...................................................................................................................... 5

8 Raw data ........................................................................................................................................................................................................................ 5

9 Verification of correct adjustment of the device ................................................................................................................. 5

9.1 Straight line measurement ........................................................................................................................................................... 5

9.2 Simple measurement of angles ................................................................................................................................................. 6

9.2.1 Measurement on a known sample, e.g. SiO /Si, with fitting of the angle of

incidence ................................................................................................................................................................................. 6

9.2.2 Measurement of the Brewster’s angle of water, of a solvent or of technical glass .. 8

10 Verification of the device regarding correct calibration ............................................................................................. 9

11 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Mathematical and physical principles of ellipsometry.....................................................10

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 23131:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 23131:2021(E)
Introduction

The ellipsometry measuring method is a phase-sensitive reflection technique using polarized light in

the optical far-field. Over a long time, ellipsometry has been established as a non-invasive measuring

method in the field of semiconductor technology — especially within the integrated production — in

the first instance as a single-wavelength, then as a multiple-wavelength and later as a spectroscopic

measuring method.

By means of ellipsometry, optical or dielectric constants of any material as well as the layer thicknesses

of at least semi-transparent layers or layer systems can be determined. Ellipsometry is an indirect

measuring method, the analysis of which is based on model optimization. The measurands, which differ

according to the procedural principle, are converted into the ellipsometric factors Ψ (Psi, amplitude

information) and Δ (Delta, phase information), based on which the physical target figures of interest

(optical or dielectric constants, layer thicknesses) will then be determined by means of a parameterized

fit.

Ellipsometry shows a high precision regarding the ellipsometric transfer quantities Ψ and Δ, which can

be equivalent to a layer thickness sensitivity of 0,1 nm for ideal layer substrate systems. As a result,

the measuring method can verify even the slightest discrepancies in the surface characteristics.

This is closely linked to the homogeneity and the isotropy of the material surface. In order to achieve

high precision, carrying out measurements at the exact same measuring point is a prerequisite for

inhomogeneous materials. The same applies to the orientation of the incident plane relative to the

material surface for anisotropic materials.

The absolute accuracy, e.g. of layer thickness values, substantially depends on the quality of the

chosen model for describing the material surface. For ideal layer substrate systems, such as SiO (ideal

transparent layer) on a Si wafer (nearly atomically smooth substrate surface with homogeneous and

isotropic material properties), the accuracy of the layer thickness can indeed reach the precision

values, since the model describes the reality of the layer substrate system in an ideal manner. For

inhomogeneous, anisotropic, contaminated, multi-component, damaged, imperfect or rough surfaces

or layers, the accuracy of the layer thickness determination can be significantly lower and generally

depends on the quality of the chosen model.

Despite these limitations, ellipsometry is a powerful procedure, which either enables material

fingerprints (without modelling) or which allows a model-based determination of optical and dielectric

constants (to the nearest 0,001) or of layer thicknesses (to the nearest 0,1 nm) within a broad layer

thickness range of approximately 0,1 nm up to approximately 10 µm (in special cases exceeding

100 µm).
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 23131:2021(E)
Ellipsometry — Principles
1 Scope

This document specifies a method for determining optical and dielectric constants in the UV-VIS-NIR

spectral range as well as layer thicknesses in the field of at-line production control, quality assurance

and material development through accredited test laboratories.

It is applicable to stand-alone measuring systems. The presentation of the uncertainty of results

conforms to ISO/IEC Guide 98-3.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

me a s ur ement (GUM: 1995)
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.2 Symbols and abbreviated terms
Symbol or
Description
abbreviated term
P polarizer
C compensator
S sample
A analyzer

POI plane of incidence of light, formed by the normal to the surface and the direction

of propagation of the incident light

POP plane of polarization of light, formed by the electric field vector and the direction

of propagation of the incident light

Ψ, Δ ellipsometric transfer quantities Psi and Delta, which serve as raw data to be stored,

e.g. in accordance with ISO/IEC 17025
φ angle of incidence between the incident light wave and the axis of incidence
d layer thickness
© ISO 2021 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 23131:2021(E)
4 Experimental boundary conditions with respect to the sample

Figures 1 and 2 schematically represent an ellipsometric measurement as a phase-sensitive reflection

technique using polarized light; both under photo-optical aspects (see Figure 1) as well as under

metrological aspects (see Figure 2).
Key
1 sample
2 POI
φ angle of incidence

Figure 1 — Schematic representation of the optical path/polarization state before and after

reflection (substrate surface, axis and angle of incidence, optical path/light wave, s- and

p-polarization)
Key
1 polarizer
2 compensator
3 sample
4 analyser
5 detector
6 light source
Figure 2 — Schematic representation of the metrological arrangement
(light source, P-C-S-A configuration)
2 © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 23131:2021(E)

The following experimental boundary conditions with respect to the sample should be agreed upon in

advance and, if relevant, be documented in the test report:

— determine/specify the measuring point (evaluation of homogeneity) and the sample orientation

(evaluation of isotropy);
— surface condition: take a micrograph of the surface if necessary;
— surface topography: if necessary, measure the surface roughness;
— further sample properties to be considered or corrected:
— curved and wedged samples;
— influence of backside reflection (for transparent samples), if present;
— surface as-delivered or cleaned;
— fixation of the sample.
5 Experimental boundary conditions with respect to the measurement

The following experimental boundary conditions with respect to the measurement should be agreed

upon in advance and, if relevant, be documented in the test report:

— indication of whether an imaging ellipsometer or a mapping ellipsometer (manual or automatic) is

concerned;

— for imaging ellipsometers the following factors are relevant: resulting size of the measuring field/

of the region of integration [FOI (field of illumination: sample surface that is illuminated by the

incident light), FOV (field of view: sample surface within the FOI from which the light collected by

the detector originates), ROI (region of interest: sample surface within the FOV that is relevant for

the measurement)];

— for mapping ellipsometers the following factors are relevant: resulting size of the measuring field/

of the region of integration [FOI (field of illumination: sample surface that is illuminated by the

incident light), FOA (field of analysis: sample surface within the FOI from which the light collected

by the detector originates)];
— ellipsometer configurations: [P-S-A, P-C-S-A, P-S-C-A or P-C-S-C-A];

— ellipsometer principle [RAE (rotating analyser ellipsometer), RPE (rotating polarizer ellipsometer),

PME (phase modulated ellipsometer), RCE (rotating compensator ellipsometer), NE (nulling

ellipsometer), SSE (step scan ellipsometer), RSE (referenced spectral ellipsometer), etc.];

— ellipsometry class [SWE (single-wavelength ellipsometry), MWE (multiple-wavelength ellipsometry),

SE (spectroscopic ellipsometry)];

— spectral range used and resulting spectral resolution, especially dependent on the light source and

the spectrometer used;

— angle of incidence, multiple-angle measurement for the verification of the model, preferably/at least

for two substantially different angles of incidence;
— orientation of sample on the sample stage;
— position of the FOV or FOA on the sample;

— alignment of the sample relative to the plane of incidence (POI) and/or relative to the plane of

polarization (POP).
© ISO 2021 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 23131:2021(E)
6 Model-correlated boundary conditions of the simulation

The following boundary conditions with respect to the simulation shall be agreed upon in advance and,

if relevant, be documented in the test report:

— definition of the ellipsometric model (substrate material, roughness, layer architecture, layer

materials, initial layer thicknesses and fit parameters);

— application of database values for optical or dielectric constants or separate experimental

determination of these constants for non-fit parameters;
— applied dispersion formulae.

The condition that the root mean square deviation (D ) between measured and simulated curve

RMS

progressions of Ψ or Δ in accordance with Formula (A.20) will become minimal, will deliver the desired

fit parameters, such as layer thickness and refractive index, as the result of an iterative fit procedure

(see Figure 3).

NOTE In accordance with ISO/IEC Guide 98-3, the term “error” is no longer used; however, root mean square

error (RMSE), instead of D , can be found in many software products.
RMS
Figure 3 — Schematic representation of the iterative fit procedure
7 Basic models
7.1 General

The ellipsometric transfer quantities Ψ and Δ represent a spectral fingerprint of the surface of the

sample and thus can also be used for material identification. When determining optical and dielectric

constants/functions as well as layer thicknesses, a model is mandatory. For this purpose, the basic

models in accordance with 7.2 to 7.6 are used.
Note Further general information is provided in References [1] to [9].
4 © ISO 2021 – All rights rese
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23131
ISO/TC 107
Ellipsometry — Principles
Secretariat: KATS
Voting begins on: Ellipsométrie — Principes
2021­01­01
Voting terminates on:
2021­02­26
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 23131:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2021
---------------------- Page: 1 ----------------------
ISO/FDIS 23131:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH­1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 23131:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions, symbols and abbreviated terms ....................................................................................................... 1

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Symbols and abbreviated terms............................................................................................................................................... 1

4 Experimental boundary conditions with respect to the sample ........................................................................ 2

5 Experimental boundary conditions with respect to the measurement ......................................................3

6 Model-correlated boundary conditions of the simulation........................................................................................ 4

7 Basic models ............................................................................................................................................................................................................. 4

7.1 General ........................................................................................................................................................................................................... 4

7.2 Bulk material (case 1 of application) ................................................................................................................................... 5

7.3 Transparent single layer (case 2 of application) ....................................................................................................... 5

7.4 Semi-transparent single layer (case 3 of application) .......................................................................................... 5

7.5 Multiple layers and periodic layers (case 4 of application) ............................................................................. 5

7.6 Effective materials (case 5 of application) ...................................................................................................................... 5

8 Raw data ........................................................................................................................................................................................................................ 5

9 Verification of correct adjustment of the device ................................................................................................................. 5

9.1 Straight line measurement ........................................................................................................................................................... 5

9.2 Simple measurement of angles ................................................................................................................................................. 6

9.2.1 Measurement on a known sample, e.g. SiO /Si, with fitting of the angle of

incidence ................................................................................................................................................................................. 6

9.2.2 Measurement of the Brewster’s angle of water, of a solvent or of technical glass .. 8

10 Verification of the device regarding correct calibration ............................................................................................. 9

11 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Mathematical and physical principles of ellipsometry.....................................................10

Bibliography .............................................................................................................................................................................................................................15

© ISO 2021 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/FDIS 23131:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non­governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/FDIS 23131:2021(E)
Introduction

The ellipsometry measuring method is a phase-sensitive reflection technique using polarized light in

the optical far-field. Over a long time, ellipsometry has been established as a non-invasive measuring

method in the field of semiconductor technology — especially within the integrated production — in

the first instance as a single-wavelength, then as a multiple-wavelength and later as a spectroscopic

measuring method.

By means of ellipsometry, optical or dielectric constants of any material as well as the layer thicknesses of

at least semi-transparent layers or layer systems can be determined. Ellipsometry is an indirect measuring

method, the analysis of which is based on model optimization. The measurands, which differ according to

the procedural principle, are converted into the ellipsometric factors Ψ (Psi, amplitude information) and Δ

(Delta, phase information), based on which the physical target figures of interest (optical or dielectric

constants, layer thicknesses) will then be determined by means of a parameterized fit.

Ellipsometry shows a high precision regarding the ellipsometric transfer quantities Ψ and Δ, which can

be equivalent to a layer thickness sensitivity of 0,1 nm for ideal layer substrate systems. As a result,

the measuring method can verify even the slightest discrepancies in the surface characteristics.

This is closely linked to the homogeneity and the isotropy of the material surface. In order to achieve

high precision, carrying out measurements at the exact same measuring point is a prerequisite for

inhomogeneous materials. The same applies to the orientation of the incident plane relative to the

material surface for anisotropic materials.

The absolute accuracy, e.g. of layer thickness values, substantially depends on the quality of the

chosen model for describing the material surface. For ideal layer substrate systems, such as SiO (ideal

transparent layer) on a Si wafer (nearly atomically smooth substrate surface with homogeneous and

isotropic material properties), the accuracy of the layer thickness can indeed reach the precision

values, since the model describes the reality of the layer substrate system in an ideal manner. For

inhomogeneous, anisotropic, contaminated, multi­component, damaged, imperfect or rough surfaces

or layers, the accuracy of the layer thickness determination can be significantly lower and generally

depends on the quality of the chosen model.

Despite these limitations, ellipsometry is a powerful procedure, which either enables material

fingerprints (without modelling) or which allows a model-based determination of optical and dielectric

constants (to the nearest 0,001) or of layer thicknesses (to the nearest 0,1 nm) within a broad layer

thickness range of approximately 0,1 nm up to approximately 10 µm (in special cases exceeding

100 µm).
© ISO 2021 – All rights reserved v
---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23131:2021(E)
Ellipsometry — Principles
1 Scope

This document specifies a method for determining optical and dielectric constants in the UV-VIS-NIR

spectral range as well as layer thicknesses in the field of at-line production control, quality assurance

and material development through accredited test laboratories.

It is applicable to stand-alone measuring systems. The presentation of the uncertainty of results

conforms to ISO/IEC Guide 98­3.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/IEC Guide 98­3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

me a s ur ement (GUM: 1995)
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.2 Symbols and abbreviated terms
Symbol or abbre-
Description
viated term
P polarizer
C compensator
S sample
A analyzer

POI plane of incidence of light, formed by the normal to the surface and the direction of

propagation of the incident light

POP plane of polarization of light, formed by the electric field vector and the direction of

propagation of the incident light

Ψ, Δ ellipsometric transfer quantities Psi and Delta, which serve as raw data to be stored,

e.g. in accordance with ISO/IEC 17025
φ angle of incidence between the incident light wave and the axis of incidence
d layer thickness
© ISO 2021 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO/FDIS 23131:2021(E)
4 Experimental boundary conditions with respect to the sample

Figures 1 and 2 schematically represent an ellipsometric measurement as a phase-sensitive reflection

technique using polarized light; both under photo-optical aspects (see Figure 1) as well as under

metrological aspects (see Figure 2).
Key
1 sample
2 POI
φ angle of incidence

Figure 1 — Schematic representation of the optical path/polarization state before and after

reflection (substrate surface, axis and angle of incidence, optical path/light wave, s- and

p-polarization)
Key
1 polarizer
2 compensator
3 sample
4 analyser
5 detector
6 light source
Figure 2 — Schematic representation of the metrological arrangement
(light source, P-C-S-A configuration)
2 © ISO 2021 – All rights reserved
---------------------- Page: 7 ----------------------
ISO/FDIS 23131:2021(E)

The following experimental boundary conditions with respect to the sample should be agreed upon in

advance and, if relevant, be documented in the test report:

— determine/specify the measuring point (evaluation of homogeneity) and the sample orientation

(evaluation of isotropy);
— surface condition: take a micrograph of the surface if necessary;
— surface topography: if necessary, measure the surface roughness;
— further sample properties to be considered or corrected:
— curved and wedged samples;
— influence of backside reflection (for transparent samples), if present;
— surface as-delivered or cleaned;
— fixation of the sample.
5 Experimental boundary conditions with respect to the measurement

The following experimental boundary conditions with respect to the measurement should be agreed

upon in advance and, if relevant, be documented in the test report:

— indication of whether an imaging ellipsometer or a mapping ellipsometer (manual or automatic) is

concerned;

— for imaging ellipsometers the following factors are relevant: resulting size of the measuring field/

of the region of integration [FOI (field of illumination: sample surface that is illuminated by the

incident light), FOV (field of view: sample surface within the FOI from which the light collected by

the detector originates), ROI (region of interest: sample surface within the FOV that is relevant for

the measurement)];

— for mapping ellipsometers the following factors are relevant: resulting size of the measuring field/

of the region of integration [FOI (field of illumination: sample surface that is illuminated by the

incident light), FOA (field of analysis: sample surface within the FOI from which the light collected

by the detector originates)];
— ellipsometer configurations: [P-S-A, P-C-S-A, P-S-C-A or P-C-S-C-A];

— ellipsometer principle [RAE (rotating analyser ellipsometer), RPE (rotating polarizer ellipsometer),

PME (phase modulated ellipsometer), RCE (rotating compensator ellipsometer), NE (nulling

ellipsometer), SSE (step scan ellipsometer), RSE (referenced spectral ellipsometer), etc.];

— ellipsometry class [SWE (single-wavelength ellipsometry), MWE (multiple-wavelength ellipsometry),

SE (spectroscopic ellipsometry)];

— spectral range used and resulting spectral resolution, especially dependent on the light source and

the spectrometer used;

— angle of incidence, multiple-angle measurement for the verification of the model, preferably/at least

for two substantially different angles of incidence;
— orientation of sample on the sample stage;
— position of the FOV or FOA on the sample;

— alignment of the sample relative to the plane of incidence (POI) and/or relative to the plane of

polarization (POP).
© ISO 2021 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO/FDIS 23131:2021(E)
6 Model-correlated boundary conditions of the simulation

The following boundary conditions with respect to the simulation shall be agreed upon in advance and,

if relevant, be documented in the test report:

— definition of the ellipsometric model (substrate material, roughness, layer architecture, layer

materials, initial layer thicknesses and fit parameters);

— application of database values for optical or dielectric constants or separate experimental

determination of these constants for non-fit parameters;
— applied dispersion formulae.

The condition that the root mean square deviation (D ) between measured and simulated curve

RMS

progressions of Ψ or Δ in accordance with Formula (A.20) will become minimal, will deliver the desired

fit parameters, such as layer thickness and refractive index, as the result of an iterative fit procedure

(see Figure 3).

NOTE In accordance with ISO/IEC Guide 98-3, the term “error” is no longer used; however, root mean square

error (RMSE), instead of D , can be found in many software products.
RMS
Figure 3 — Schematic representation of the iterative fit procedure
7 Basic models
7.1 General

The ellipsometric transfer quantities Ψ and Δ represent a spectral fingerprint of the surface of the

sample and thus can also be used for material identification. When determi
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.