ISO 11952:2014
(Main)Surface chemical analysis — Scanning-probe microscopy — Determination of geometric quantities using SPM: Calibration of measuring systems
Surface chemical analysis — Scanning-probe microscopy — Determination of geometric quantities using SPM: Calibration of measuring systems
ISO 11952:2014 specifies methods for characterizing and calibrating the scan axes of scanning-probe microscopes for measuring geometric quantities at the highest level. It is applicable to those providing further calibrations and is not intended for general industry use, where a lower level of calibration might be required.
Analyse chimique des surfaces — Microscopie à sonde à balayage — Détermination des quantités géométriques en utilisant des microscopes à sonde à balayage: Étalonnage des systèmes de mesure
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INTERNATIONAL ISO
STANDARD 11952
First edition
2014-05-15
Surface chemical analysis — Scanning-
probe microscopy — Determination
of geometric quantities using SPM:
Calibration of measuring systems
Analyse chimique des surfaces — Microscopie à sonde à balayage
— Détermination des quantités géométriques en utilisant des
microscopes à sonde à balayage: Étalonnage des systèmes de mesure
Reference number
ISO 11952:2014(E)
©
ISO 2014
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ISO 11952:2014(E)
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© ISO 2014
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ISO 11952:2014(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Characteristics of scanning-probe microscopes . 4
5.1 Components of a scanning-probe microscope . 4
5.2 Metrological categories of scanning-probe microscopes . 5
5.3 Block diagram of a scanning-probe microscope . 5
5.4 Calibration interval . 7
6 Preliminary characterization of the measuring system . 8
6.1 Overview of the instrument characteristics and influencing factors to be investigated . 8
6.2 Waiting times after interventions in the measuring system (instrument installation,
intrinsic effects, carrying out operation, warm-up, tip/specimen change, etc.) .10
6.3 External influences .11
6.4 Summary .11
7 Calibration of scan axes .12
7.1 General .12
7.2 Measurement standards .12
7.3 Xy-scanner guidance deviations of the x- and y-axes (xtz, ytz) .13
7.4 Calibration of x- and y-axis (Cx, Cy) and of rectangularity (ϕxy) and determination of
deviations (xtx, yty, ywx).17
7.5 Calibration of the z-axis C , ϕ , and ϕ , and determination of the deviations ztz, zwx,
z xz yz
and zwy . 25
7.6 3D measurement standards for alternative and extended calibration .32
8 Report of calibration results .37
9 Uncertainties of measurement .38
9.1 General .38
9.2 Vertical measurand (height and depth).38
10 Report of results (form) .40
Annex A (informative) Example of superposition of disturbing influences in the
topography image .41
Annex B (informative) Sound investigations: Effects of a sound proofing hood .43
Annex C (informative) Thermal isolation effect of a sound proofing hood/measuring cabin .45
Annex D (informative) Handling of contaminations in recorded topography images .47
Annex E (informative) Step height determination: comparison between histogram and
ISO 5436-1 method .48
Annex F (normative) Uncertainty of measurement for lateral measurands (pitch,
position, diameter) .50
Bibliography .56
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ISO 11952:2014(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 201, Surface chemical analysis, Subcommittee
SC 9, Scanning probe microscopy.
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ISO 11952:2014(E)
Introduction
The progress of miniaturization in semiconductor structuring, together with the rapid advance of
many diverse applications of nanotechnology in industrial processes, calls for reliable and comparable
[9]
quantitative dimensional measurements in the micro- and submicrometre range. Currently, a
measurement resolution, in or below the nanometre region, is frequently required. Conventional optical
or stylus measurement methods or coordinate measuring systems are not able to offer this level of
resolution.
For this reason, scanning-probe microscopes (SPMs) are increasingly employed as quantitative
measuring instruments. Their use is no longer confined only to research and development, but has also
been extended to include industrial production and inspection.
For this category of measuring instrument, standardized calibration procedures need to be developed,
for example, as have been established already long ago for contact stylus instruments (see ISO 12179).
For efficient and reliable calibration of SPMs to be carried out, the properties of the measurement
standards used need to be documented and be accounted for in the calibration (see Figure 1) and, at the
same time, the procedure for the calibration should be clearly defined.
Only if this prerequisite is satisfied, will it be possible to perform traceable measurements of geometrical
quantities.
Figure 1 — Traceability chain for scanning-probe microscopes
NOTE The calibration of a user’s SPM by means of traceably calibrated measurement standards is the
object of this International Standard (done by the user).
A scanning-probe microscope is a serially operating measuring device which uses a probe with a tip of
adequate fineness to trace the surface of the object to be measured by exploitation of a local physical
interaction (such as the quantum-mechanical tunnel effect, interatomic or intermolecular forces, or
evanescent modes of the electromagnetic field). The probe and the object to be measured are being
displaced in relation to one another in a plane (hereinafter referred to as the x-y-plane) according to a
[10]
while the signal of the interaction is recorded and can be used to control the distance
defined pattern,
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ISO 11952:2014(E)
between probe and object. In this International Standard, signals are considered which are used for the
determination of the topography (hereinafter called the “z-signal”).
This International Standard covers the verification of the device characteristics necessary for the
[11]
measurement of geometrical measurands and the calibration of the axes of motion (x, y, z), i.e. the
traceability to the unit of length via measurement on traceable lateral, step height, and 3D measurement
standards (see Figure 2).
While this International Standard aims at axis calibrations at the highest level and is thereby intended
primarily for high-stability SPMs, a lower level of calibration might be required for general industry use.
Key
1 measurement standards for verification purposes
1a flatness
1b probe shape
2 measurement standards for calibration purposes
2a 1D and 2D lateral
2b step height
3 calibration of the measurement standards by reference instruments (certified calibration, measurement
value including uncertainty)
Figure 2 — Verification and calibration of scanning-probe microscopes with test specimens and
measurement standards
This International Standard is mainly based on the guideline VDI/VDE 2656, Part 1, drafted by a
guideline committee of the VDI (Verein Deutscher Ingenieure/Association of German Engineers) in the
years 2004 to 2008, with the final whiteprint of that guideline being released in June 2008.
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INTERNATIONAL STANDARD ISO 11952:2014(E)
Surface chemical analysis — Scanning-probe microscopy
— Determination of geometric quantities using SPM:
Calibration of measuring systems
1 Scope
This International Standard specifies methods for characterizing and calibrating the scan axes of
scanning-probe microscopes for measuring geometric quantities at the highest level. It is applicable to
those providing further calibrations and is not intended for general industry use, where a lower level of
calibration might be required.
This International Standard has the following objectives:
— to increase the comparability of measurements of geometrical quantities made using scanning-
probe microscopes by traceability to the unit of length;
— to define the minimum requirements for the calibration process and the conditions of acceptance;
— to ascertain the instrument’s ability to be calibrated (assignment of a “calibrate-ability” category to
the instrument);
— to define the scope of the calibration (conditions of measurement and environments, ranges of
measurement, temporal stability, transferability);
— to provide a model, in accordance with ISO/IEC Guide 98-3, to calculate the uncertainty for simple
geometrical quantities in measurements using a scanning-probe microscope;
— to define the requirements for reporting results.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 11039, Surface chemical analysis — Scanning-probe microscopy — Measurement of drift rate
ISO 18115-2, Surface chemical analysis — Vocabulary — Part 2: Terms used in scanning-probe microscopy
IEC/TS 62622, Artificial gratings used in nanotechnology — Description and measurement of dimensional
quality parameters
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115-2 and IEC/TS 62622
and the following apply.
3.1
scanner bow
additional deflection in the z-direction when the scanner is displaced in the x-y-direction
Note 1 to entry: Scanner bow is also known as out-of-plane motion (see also xtz, ytz in Clause 4).
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ISO 11952:2014(E)
3.2
look-up table
table in which a set of correction factors for the scanner are filed for different modes of operation (scan
ranges, scan speeds, deflections, etc.)
3.3
step height
height of an elevation (bar) or depth of a groove (ISO 5436-1), in atomic surfaces, the distance between
neighbouring crystalline planes
3.4
levelling
correction of the inclination between the ideal x-y-specimen plane and the x-y-scanning plane
4 Symbols
x, y, z position value related to the respective axis
C , C , C calibration factors for the x-, y-, and z-axes
x y z
h step height
w width of a structure of the specimen
th
N i pitch value in a profile used for the determination of the pitch/period (number of pitch values i
j
over all lines j = 1,., Nj)
p pitch or period in the x-direction
x
p pitch or period in the y-direction
y
a vector in the x-direction of a grating (not to be confused with p )
x x
a vector in the y-direction of a grating (not to be confused with p )
y y
γ non-orthogonality of 2D gratings
xy
P-V peak-to-valley value
r radius
Rq (Sq) root mean square deviation of the assessed roughness profile (Rq) or of the assessed area (Sq)
T temperature
α thermal expansion coefficient
m
T temperature of the air
L
T temperature of the specimen during measurement
m
j angle of rotation about the x-axis
x
j angle of rotation about the y-axis
y
j angle of rotation about the z-axis
z
θ levelling angle
x value of the measurement standard for shift in the x-direction
L
x shift in the x-direction measured with the x-displacement transducer
m
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ISO 11952:2014(E)
xtx positional deviation Δx measured along an x-coordinate line
xty straightness deviation Δy measured along an x-coordinate line
xtz straightness deviation Δz measured along an x-coordinate line
xrx rotational deviation j measured along an x-coordinate line
x
xry rotational deviation j measured along an x-coordinate line
y
xrz rotational deviation j measured along an x-coordinate line
z
xwy measured rectangularity deviation in the coordinate plane x-y
xwz measured rectangularity deviation in the coordinate plane x-z
y value of the measurement standard for displacement in the y-direction
L
y displacement measured with the y-displacement transducer in the y-direction
m
ytx positional deviation Δx measured along a y-coordinate line
yty straightness deviation Δy measured along a y-coordinate line
ytz straightness deviation Δz measured along a y-coordinate line
yrx rotational deviation j measured along a y-coordinate line
x
yry rotational deviation j measured along a y-coordinate line
y
yrz rotational deviation j measured along a y-coordinate line
z
ywz rectangularity deviation measured in the coordinate plane y-z
z value of the measurement standard for displacement in the z-direction
L
z displacement in the z-direction measured with z-displacement transducer
m
ztx straightness deviation Δx measured along a z-coordinate line
zty straightness deviation Δy measured along a z-coordinate line
ztz straightness deviation Δz measured along a z-coordinate line
zrx rotational deviation j measured along a z-coordinate line
x
zry rotational deviation j measured along a z-coordinate line
y
zrz rotational deviation j measured along a z-coordinate line
z
cos(φ ) rotational correction, e.g. in pitch measurement
i
cos(θ ) tilt-related correction, e.g. in pitch measurement
i
λ short-wavelength filter (see ISO 4287 for details)
s
λ long-wavelength filter (see ISO 4287 for details)
c
Λ correlation length
ϕ angle between the x- and y-direction, counterclockwise
xy
ϕ angle between the x- and z-direction, counterclockwise
xz
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ISO 11952:2014(E)
ϕ angle between the y- and z-direction, counterclockwise
yz
Rqx noise in the x-direction
Rqy noise in the y-direction
Rqz (Sqz) noise in the z-direction in a measured profile (or within a measured area)
v scan speed (i.e. distance travelled by the probe tip per unit time, not to be confused with the scan
rate, i.e. the number of scanlines recorded per unit time)
5 Characteristics of scanning-probe microscopes
5.1 Components of a scanning-probe microscope
Key
1 x-y-scanner
2 z-scanner
3 position detector
4 probe
5 specimen
6 coarse z-approach, i.e. move the probe or the specimen in the vertical direction to bring it close enough to the
specimen or probe, respectively (afterwards, start automatically approach techniques).
7 coarse x-y-positioning, i.e. move the specimen or probe laterally close to or into the region of interest on the
specimen, respectively
Figure 3 — Schematic sketch of a scanning-probe microscope
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ISO 11952:2014(E)
Several components shown in Figure 3 are defined in ISO 18115-2. In this International Standard, they
fulfil the following functions.
— Probe: equipped with a tip at its apex. This probes the specimen surface, exploiting a local physical
interaction whose changes can be detected, e.g. as cantilever bending in the case of an atomic force
microscope.
— Position detector: Transformation of the probe’s interaction response (e.g. bending or oscillation of
the cantilever) into an electrical signal.
— z-scanner: Element for the realisation of the vertical tracking of the specimen/probe distance during
x-y-scanning to a constant value of the physical interaction used for distance control (e.g. of the
action of force on the probe in the case of an atomic force microscope), to ensure an approximately
constant distance between specimen and probe.
— x-y-scanner: Element for realisation of the lateral displacement of the probe (or of the specimen) in
the x-y-plane (the plane parallel to the seating face of the specimen), which is used, among other
things, to record a location-dependent interaction signal that contains information about a local
property of the specimen (above all, the local height).
— Specimen holder: where appropriate, with coarse positioning and coarse approach mechanics.
— Casing/mounting: Structure for mounting the scanner and specimen.
5.2 Metrological categories of scanning-probe microscopes
SPMs can generally be subdivided into the three following categories, depending on their metrological
equipment:
— category A: Reference instruments with integrated laser interferometers, allowing direct
1)
traceability, via the wavelength of the laser used, to the SI unit of length.
— category B: SPMs with position measurement using displacement transducers, e.g. capacitive/inductive
sensors, strain gauges or encoders calibrated by temporarily connecting laser interferometers to
the instrument or by making measurements on high-quality measurement standards. A distinction
is made between the following two types:
— those with active position control: tracking to a scheduled position by means of a closed loop
(so-called closed-loop configuration);
— those with position measurement but without a closed loop for position control (so-called open-
loop configuration).
— category C: SPMs in which the position is determined from the electrical voltage applied to the
adjustment elements and, if need be, corrected using the look-up table. Calibration is against
measurement standards.
These definitions of metrological categories imply that it is not possible for certain instruments to
be assigned to a single category, but that, with respect to their scan axes, they need to be considered
separately.
5.3 Block diagram of a scanning-probe microscope
The block diagram shown in Figure 4 has been obtained from the schematic diagram of an SPM in
Figure 3. The characteristics of the essential components are given below and need to be investigated
individually in the course of verification and calibration.
1) Instruments of this category are often referred to as “metrological SPMs”, although the definition of a
“metrological SPM” in ISO 18115-2:2010/Amd.1 (to be published) does not necessarily imply laser-interferometric
position control.
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ISO 11952:2014(E)
For category C:
— casing/mounting (mechanical, acoustic, electromagnetic, and thermal characteristics);
— specimen holder, where appropriate with coarse positioning and coarse approach mechanics
(acoustic, mechanical, and thermal characteristics);
— z-scanner;
— x-y-scanner;
— detector loop, e.g. using the beam deflection method, with a beam on the rear side of the cantilever in
the case of an atomic force microscope and detection of the reflected beam from the rear side of the
cantilever with a position-sensitive photodiode. The signal of the position-dependent photodiode
serves as input to the feedback loop of the z-scanner in order to keep the set-point constant;
— probe.
Additionally, for category B:
— category B2: x-, y-, and/or z-displacement transducer, e.g. encoder, capacitive, or inductive
displacement transducer or strain gauge;
— category B1: where appropriate, active (closed-loop) position control.
Additionally, for category A:
Traceability by integrated laser interferometers, i.e. systems as for category B, but equipped with
— integrated laser interferometers for position measurement/control and
— where appropriate, additionally provided with angle sensors.
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ISO 11952:2014(E)
z(x,y)
internal device
signature
control and
data recording
x, y-position z-measurement
value
x, y control loop z control circuit z-position sensor
x, y position sensors position detector
x, y-scanner
probe z-scanner
z
y
x
measurement object
x, y-block z-block
Figure 4 — Block diagram of a scanning-probe microscope
The classification above is a first rough estimation of the effort necessary to achieve the desired
accuracy of calibration. It is not necessary, for example, to purchase a set of measurement standards
with minimum uncertainties of measurement for the calibration of category C instruments. Less
sophisticated measurement standards are usually sufficient here.
5.4 Calibration interval
The interval at which the instrument will need to be calibrated depends on the type of instrument
(i.e. the metrological category), its stability, especially with respect to time, the intended purpose of
the measurements and the constancy of the ambient conditions. As most calibrations are of a complex
nature, and thus, are labour- and time-intensive, a compromise needs to be found between the cost of
calibration and the measurement uncertainty which can be tolerated.
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ISO 11952:2014(E)
Generally, the following repetition patterns for calibrations (K) and measurements (M) are suitable.
KMM …, KMM . for instruments of high stability in the medium term: calibration is necessary only at defined
intervals of time, e.g. once weekly/monthly/yearly.
KM, KM, KM … for instruments with acceptable short-term but bad long-term stability: calibration is neces-
sary before each measurement.
KMK, KMK . when the maximum precision of the instrument is to be used for measurements with as
small an uncertainty of measurement as possible or for instruments which are unstable
with time and therefore require the drift in their characteristics to be taken into account as
far as possible.
Especially after putting into operation an SPM which is new or has been modified or relocated, it is
advisable in the initial phase to repeat a defined calibration pattern several times in order to gain
experience with the stability of the instrument.
6 Preliminary characterization of the measuring system
6.1 Overview of the instrument characteristics and influencing factors to be investigat-
ed
In order to define a calibration schedule for a particular SPM, three groups of influencing factors need
to be investigated in detail (see Figure 5): the instrument’s characteristics (as described above), the
ambient conditions, and the effects of operation by the user.
These investigations should be carried out in the following order, prior to the calibration process proper:
a) investigation of the waiting time after putting the instrument into operation (warm-up, initial drift,
etc.) (see 6.2);
b) investigation of the waiting time after changing the specimen or probe or other interventions before
sufficiently stable conditions of measurement are reached (see 6.2);
c) the influence of the ambient conditions, producing a temporary drift and/or changes in temperature,
air humidity, air flow, mechanical, and acoustic vibrations, electromagnetic interference, etc.
(see 6.3);
d) the noise of the instrument (see 6.3 and also Table 1);
e) xy-scanner/z-scanner-guidance deviations (cross-talk from one scan axis to other axes, which can,
at times, be detectable only by repeated measurements) (see 7.3);
f) long-term stability (reproducibility) (see 5.4).
These investig
...
DRAFT INTERNATIONAL STANDARD ISO/DIS 11952
ISO/TC 201/SC 9 Secretariat: KATS
Voting begins on Voting terminates on
2011-10-13 2012-03-13
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ ORGANISATION INTERNATIONALE DE NORMALISATION
Surface chemical analysis — Scanning probe microscopy —
Determination of geometric quantities using SPM: Calibration of
measuring systems
Analyse chimique des surfaces — Microscopie à sonde à balayage — Détermination des quantités
géométriques en utilisant des microscopes à sonde à balayage: Étalonnage des systèmes de mesure
ICS 71.040.40
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Conformément aux dispositions de la Résolution du Conseil 15/1993, ce document est distribué
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To expedite distribution, this document is circulated as received from the committee
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Pour accélérer la distribution, le présent document est distribué tel qu'il est parvenu du
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THIS DOCUMENT IS A DRAFT CIRCULATED FOR COMMENT AND APPROVAL. IT IS THEREFORE SUBJECT TO CHANGE AND MAY NOT BE
REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME
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THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION.
© International Organization for Standardization, 2011
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ISO/DIS 11952
Copyright notice
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under the applicable laws of the user’s country, neither this ISO draft nor any extract from it may be
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ii © ISO 2011 – All rights reserved
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ISO/DIS 11952
Contents Page
1 Scope .1
2 Normative references, terms and definitions .2
2.1 Normative references .2
2.2 Terms used.3
3 Symbols .4
4 Characteristics of scanning probe microscopes .5
4.1 Components of a scanning probe microscope .5
4.2 Metrological categories of scanning probe microscopes.6
4.3 Block model of a scanning probe microscope.6
4.4 Calibration intervals .8
5 Preliminary characterization of the measuring system.8
5.1 Overview of the device characteristics and influence factors to be investigated.8
5.2 Waiting times after interventions into the measuring system).9
5.2.1 Potential causes of drift .10
5.2.2 Procedure .10
5.3 External influences.10
5.3.1 Kinds of internal influences.10
5.3.2 Consequences of external influences and countermeasures .10
5.4 Summary.11
6 Calibration .11
6.1 Standards .11
6.1.1 Requirements for standards.12
6.1.2 Handling of standards.12
6.2 Guidance deviations of the x- and y-axes (xtz, ytz) .12
6.2.1 Definition of guidance deviations from the plane (z-plane) .12
6.2.2 Measurement strategy.13
6.2.3 Flatness standards .14
6.2.4 Measurements.14
6.2.5 Evaluation.14
6.2.6 Summary.14
6.2.7 Extended calibration measurements.14
6.3 Calibration of x- and y-axis (Cx, Cy), .15
6.3.1 Definition of pitch p and p and rectangularity φφ in the x-y-plane .15
φφ
x y xy
6.3.2 Measurement strategy.16
6.3.3 Selection of lateral standards.16
6.3.4 Basic calibration: adjustments and measurements.17
6.3.5 Extended calibrations (scan speed, angle, eccentric measurements) .18
6.3.6 Evaluation.19
6.3.7 Extended evaluations: non-linearity of the x-y-axis.21
6.3.8 Summary.22
iii
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ISO/DIS 11952
6.4 Calibration of the z-axis Cz, φφφφ , φφφφ and determination of the deviations ztz, zwx, zwy .22
xz yz
6.4.1 Definitions of the step height.22
6.4.2 Measurement strategy .23
6.4.3 Selection of step height standards.23
6.4.4 Basic calibration: Adjustments and measurements.23
6.4.5 Extended calibrations .25
6.4.6 Evaluations .25
6.4.7 Summary .28
6.5 3D standards for alternative and extended calibration .28
6.5.1 Requirements for 3D standards.29
6.5.2 Selection of the 3D standards.30
6.5.3 Carrying-out of the basic calibration.30
6.5.4 Evaluation of the measurements .30
6.5.5 Extended calibrations .31
6.5.6 Advantages and disadvantages of the 3D standard.32
7 Report of calibration results.32
8 Uncertainties of measurement.33
8.1 Vertical measurand (height, depth) .33
9 Report of results (form) .35
Annex A (informative) Exemplary superposition of disturbing influences in the topography .36
Annex B (informative) Sound investigations: Effects of a sound proofing hood .37
Annex C (informative) Thermal isolation effect of a sound proofing hood/measuring cabin.39
Annex D (informative) Control parameters and scan speed; handling of contaminations .41
Annex E (informative) Step height determination: comparison histogram and ISO-5436 method .42
Annex F (normative) Uncertainty of measurement for lateral measurands .44
Bibliography…………………………………………….…………………………………………………………….49
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ISO/DIS 11952
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 9, Scanning probe microscopy.
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ISO/DIS 11952
Introduction
The progress of miniaturization in semiconductor structuring, just as the fast advance of the extremely
versatile nanotechnology applications, in a great number of industrial processes calls for reliable and
comparable quantitative dimensional measurements in the micro- and submicrometre range [1]. By now
resolutions in or even below the nanometre region are already frequently required, i.e. resolutions
conventional optical or stylus measurement methods or coordinate measuring systems are not able to offer.
This is why scanning probe microscopes (SPM) are increasingly employed as quantitative measuring
instruments, their use being no longer confined only to research and development but increasingly extended
also to industrial production and inspection.
For this category of measuring instruments, too, standardized calibration procedures therefore need to be
developed as have, for example, been established already long ago for contact stylus instruments
(ISO 12179). In many cases, specifically developed measurement standards are used here. For calibrations of
SPMs to be carried out not only reliably but also efficiently, the properties of the standards used should have
been documented and be accounted for in the calibration and, at the same time, the procedure for the
calibration should be clearly defined.
Only if this prerequisite is provided will it be possible to perform traceable measurements of geometrical
quantities.
This standard is mainly based on the guideline VDI/VDE 2656 – Part 1 drafted by a guideline committee of
VDI (Verein Deutscher Ingenieure, Association of German Engineers) in the years 2004 to 2008, with the final
whiteprint of that guideline being released in June 2008.
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'5$)7,17(51$7,21$/67$1'$5' ISO/DIS 11952
Surface chemical analysis — Scanning probe microscopy —
Determination of geometric quantities using SPM: Calibration of
measuring systems
1 Scope
This standard is restricted to scanning probe microscopes and their characterization and dimensional
calibration. A scanning probe microscope is a serially operating measuring device which uses a probe with a
tip of adequate fineness to trace the surface of the object to be measured by exploitation of a local physical
interaction (such as the quantum-mechanical tunnel effect, interatomic or intermolecular forces, evanescent
modes of the electromagnetic field). The probe and the object to be measured are being displaced in relation
to one another in a plane (hereinafter referred to as the x-y- plane) according to a defined pattern [2], while the
signal of the interaction is recorded and can be used to control the distance between probe and object. In this
standard signals are considered which are used for the determination of the topography (hereinafter called "z-
signal").
This ISO standard covers the verification of the device characteristics necessary for the measurement of
geometrical measurands, and the calibration of the axes of motion (x, y, z), i.e. the traceability to the unit of
length via measurement on traceable lateral, step height and 3D standards (figure 1). Such a
characterization and calibration of the SPM (figure 2) is a prerequisite for its use for dimensional
measurements e. g. in industry [3].
Figure 1: Traceability chain for scanning probe microscopes:
The calibration of user’s SPM by means of traceably calibrated standards is the object of this standard (“done by the user”)
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ISO/DIS 11952
With the implementation of this standard the following objectives are pursued:
• increase in the comparability of measurements of geometrical quantities using scanning probe
microscopes by traceability to the unit of length
• definition of minimum requirements for the calibration process and the conditions of acceptance
• ascertainment of the calibratability (assignment to calibratability categories)
• fixing of the scope of a calibration (conditions of measurement and environments, ranges of measurement,
temporal stability, transferability)
• provision of a model according to GUM to calculate the uncertainty for simple geometrical quantities in
measurements using a scanning probe microscope
• definition of the requirements for a result report
Figure 2: Verification and calibration of scanning probe microscopes with samples and standards
2 Normative references, terms and definitions
2.1 Normative references
The following referenced documents are indispensable for the application 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 18115-2 Surface chemical analysis – Vocabulary – Part 2 Terms used in scanning probe microscopy
(including amendments)
• ISO Guide 30: 1992, Terms and definitions used in connection with reference materials
• ISO Guide 34: 1996, Quality system guidelines for the production of reference materials
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ISO/DIS 11952
• ISO 11039 Surface chemical analysis — Scanning probe microscopy — Definition and measurement
methods of drift rates of SPM
The following documents are not mandatory for the basic dimensional calibration of SPM, but may prove
indispensable depending on the intended applications of the SPM:
• ISO 11775 Surface chemical analysis — Scanning probe microscopy — Determination of cantilever normal
spring constants
• ISO 11939 Surface chemical analysis — Scanning probe microscopy — Standards on the measurement of
angle between an AFM tip and surface and its certified reference material
• ISO 13095 Surface chemical analysis — Scanning probe microscopy — procedure for in-situ
characterization of AFM probes used for nanostructure measurements
• ISO 13096 Surface chemical analysis — Scanning probe microscopy — Guide to describe AFM probe
properties
• ISO/IEC TS 13126 Nanotechnologies — Artificial gratings used in nanotechnology — description and
measurement of dimensional quality parameters
Furthermore, in the field of surface measurement, a corpus of standards is already available for contact stylus
instruments. So definitions and terms according to these standards are used here especially for:
• definitions of device components: ISO 3274
• calibration standards: ISO 5436-1
• definition of surface (profile) characteristics: ISO 4287
• conditions of measurement and evaluation: ISO 4288
• definitions of properties of general-purpose microscopes: ISO 12853
• calibration of contact stylus instruments: ISO 12179
2.2 Terms used
In addition to acronyms and terms defined in ISO 18115 and the other standards mentioned above, the
following terms are used:
scanning sample During scanning, the sample is displaced in the x-y-direction and, if need be, tracked in
the z-direction. The probe acts as a zero detector.
scanning probe During scanning, the probe is displaced in the x-y-direction and tracked in the z-
direction of the surface.
scanner bow or When displaced in the x-y-direction, the scanner is accidentally deflected in the z-
direction (see also xtz, ytz).
out-of-plane motion
look-up table(s) in which correction factors for the scanner for different modes of operation
table (ranges, speeds, deflections.) are filed
open loop position values for the x- and y-axis are not used for position control
closed loop For scanning, the position values measured by a displacement transducer are used to
track the x- and y-axis via a control to scheduled position values.
position centre of gravity of a structure or of a feature in coordinates of the device
step height height of an elevation or depth of a groove (ISO 5436-1), in atomic surfaces the
distance between neighbouring crystalline planes
correction of the inclination between ideal x-y-sample plane and x-y-scanning plane
levelling
distance distance of two positions on the surface; it is defined as the distance of the centres of
gravity of the respective structures unless otherwise stated
pitch mean distance of similar structural features of the surface (period)
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ISO/DIS 11952
3 Symbols
x, y, z position value related to the respective axis
C , C , C calibration factor for the x-, y- and z-axis
x y z
h step height
w width of a structure of the sample
N number of pitch values i over all lines j = 1,., Nj
j
(o, x , y , z ) rectangular coordinate system with the coordinate origin o and the coordinate axes x,
R R R
y and z (abscissa, ordinate and applicate axes)
p pitch or period in the x-direction
x
p pitch or period in the y-direction
y
a vector in x-direction of a grating (not to be confounded with p )
x x
a vector in y-direction of a grating (not to be confounded with p )
y y
γ non-orthogonality of 2D gratings
xy
P-V peak-to-valley value
r radius
Rq (Sq) root mean square deviation of the assessed roughness profile (Rq, so-called rms
value) or of the assessed area (Sq)
T temperature
α thermal expansion coefficient
m
temperature of air
ϑ
temperature of sample in the measurement
T
m
angle of rotation about x-axis
ϕ
x
angle of rotation about y-axis
ϕ
y
angle of rotation about z-axis
ϕ
z
levelling angle
Θ
x value of the standard for shift in the x-direction
L
x shift in the x-direction measured with the x-displacement transducer
m
xtx
positional deviation Δx measured along an x-coordinate line
xty
straightness deviation Δy measured along an x-coordinate line
xtz
straightness deviation Δz measured along an x-coordinate line
xrx
rotational deviation ϕ measured along an x-coordinate line
x
xry
rotational deviation ϕ measured along an x-coordinate line
y
xrz
rotational deviation ϕ measured along an x-coordinate line
z
xwy measured rectangularity deviation in the coordinate plane xy
xwz measured rectangularity deviation in the coordinate plane xz
y value of the standard for displacement in the y -direction
L L
y displacement measured with the y-displacement transducer in the y-direction
m
ytx
positional deviation Δx measured along a y-coordinate line
yty
straightness deviation Δy measured along a y-coordinate line
ytz
straightness deviation Δz measured along a y-coordinate line
yrx
rotational deviation ϕ measured along a y-coordinate line
x
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ISO/DIS 11952
yry
rotational deviation ϕ measured along a y-coordinate line
y
yrz
rotational deviation ϕ measured along a y-coordinate line
z
ywz measured rectangularity deviation in the coordinate plane yz
z value of the standard for displacement in the z -direction
L L
z displacement in the z-direction measured with z-displacement transducer
m
ztx
straightness deviation Δx measured along a z-coordinate line
zty straightness deviation Δy measured along a z-coordinate line
ztz straightness deviation Δz measured along a z-coordinate line
zrx rotational deviation ϕ measured along a z-coordinate line
x
zry rotational deviation ϕ measured along a z-coordinate line
y
zrz
rotational deviation ϕ measured along a z-coordinate line
z
rotational correction e. g. in pitch measurement
cos(ϕ )
i
tilt-related correction e. g. in pitch measurement
cos(θ )
i
short wavelength filter (see ISO 4287 for details)
λ
s
long wavelength filter (see ISO 4287 for details)
λ
c
correlation length
Λ
angle between x- and y-direction, counterclockwise
φ
xy
angle between x- and z-direction, counterclockwise
φ
xz
angle between y- and z-direction, counterclockwise
φ
yz
noise in x-direction
Rqx
Rqy noise in y-direction
Rqz (Sqz) noise in z-direction in a measured profile (within a measured area, resp.)
v scan speed (i.e. distance travelled by the tip per unit of time, not to be confounded
with the scan rate, i.e. the number of scanlines recorded per unit of time)
4 Characteristics of scanning probe microscopes
4.1 Components of a scanning probe microscope
Figure 3: Schematic sketch of a scanning probe microscope system
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ISO/DIS 11952
Several components shown in Figure 3 are defined in ISO 18115. Here they fulfil the following functions:
Probe: equipped with a tip at its apex, it probes the sample surface exploiting a local physical interaction
whose changes can be detected, e.g. as cantilever bending in the case of an atomic force microscope
Position detector: Transformation of the probe’s interaction response (e. g. bending or oscillation of the
cantilever) into an electrical signal.
z-scanner: Adjusting element for tracking the sample-probe distance during x-y-scanning to a constant value
of the physical interaction used for distance control (e.g. of the action of force on the probe in the case of an
atomic force microscope), approximately to ensure a constant distance between sample and probe.
x-y-scanner: Adjusting element for lateral displacement of the probe (alternatively: of the sample) in the x-y-
plane (plane parallel to the seating face of the sample), which is used, among other things, to record a
location-dependent interaction signal that contains information about the local property of the sample (here
above all the topography: local height).
Sample holder: where appropriate, with coarse positioning and coarse approach mechanics.
Casing/mounting: Construction and materials between mountings for scanner and sample forming the
measurement circle.
4.2 Metrological categories of scanning probe microscopes
SPMs can generally be subdivided into the three following categories depending on their metrological
equipment:
A) Reference devices with integrated laser interferometers allowing direct traceability via the wavelength of
1
the laser used to the SI unit of length
B) SPMs with position measurement using displacement transducers, e.g. capacitive/inductive sensors,
strain gauges, encoders calibrated by temporarily connecting laser interferometers to the device or by
measuring on high-quality standards. Two types are to be distinguished here:
B1) active position control: tracking to scheduled position by means of a closed loop (so-called closed-
loop configuration)
B2) with position measurement but without closed loop for position control (so-called open-loop
configuration)
C) SPMs in which the position is determined from the electrical voltage applied to the adjusting elements and,
if need be, corrected using the look-up table; calibration against standards
This definition of metrological categories implies that it is not possible for certain devices to be assigned as a
whole to a single category but that with respect to their scan axes they must be considered separately.
4.3 Block model of a scanning probe microscope
From the schematic SPM model in Figure 3, the abstract block model in Figure 4 is obtained. The
characteristics of its essential components are given below and need to be investigated individually in the
course of verification and calibration.
For category C:
• casing/mounting (mechanical, acoustic, electromagnetic and thermal characteristics)
• sample holder, where appropriate with coarse positioning and coarse approach mechanics (accoustic
1
Instruments of category A are often referred to as “metrological SPM”, although the definition of a “metrological SPM” in
ISO 18115-2 Amd1 does not necessarily imply l
...
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