ISO 13095:2014

Surface Chemical Analysis — Atomic force microscopy — Procedure for in situ characterization of AFM probe shank profile used for nanostructure measurement

ISO 13095:2014 specifies two methods for characterizing the shape of an AFM probe tip, specifically the shank and approximate tip profiles. These methods project the profile of an AFM probe tip onto a given plane, and the characteristics of the probe shank are also projected onto that plane under defined operating conditions. The latter indicates the usefulness of a given probe for depth measurements in narrow trenches and similar profiles. This International Standard is applicable to the probes with radii greater than 5u0, where u0 is the uncertainty of the width of the ridge structure in the reference sample used to characterize the probe.

Analyse chimique des surfaces — Microscopie à balayage de sonde — Procédure pour la caractérisation in situ des sondes AFM utilisées pour mesurer la nanostructure

General Information

• Status: Published
• Publication Date: 04-Aug-2014
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 9 - Scanning probe microscopy
• Drafting Committee: ISO/TC 201/SC 9/WG 5 - Calibration of probes
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 25-Jun-2021

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13095
First edition
2014-07-15
Surface Chemical Analysis — Atomic
force microscopy — Procedure for in
situ characterization of AFM probe
shank profile used for nanostructure
measurement
Analyse chimique des surfaces — Microscopie à balayage de sonde
— Procédure pour la caractérisation in situ des sondes AFM utilisées
pour mesurer la nanostructure
Reference number
ISO 13095:2014(E)
©
ISO 2014

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ISO 13095:2014(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2014
All rights reserved. Unless otherwise specified, 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
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Published in Switzerland
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ISO 13095:2014(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
5 Procedure for probe characterization . 4
5.1 Methods for the determination of AFM probe shapes . 4
5.2 Reference sample setting . 5
5.3 Requirements of AFM and AFM imaging . 6
5.4 Measurement of probe shank profile . 7
5.5 Uncertainty of the measurement of the probe shank profile. 9
6 Reporting of probe characteristics .10
Annex A (informative) Dependence of AFM images on measurement mode and settings .12
Annex B (normative) Reference sample preparation .15
Annex C (informative) Example of a reference structure .18
Annex D (informative) Results of EPSC measurement repeatability test .20
Annex E (informative) Plane correction for probe shank profile analysis .22
Annex F (informative) Example of a report .23
Bibliography .25
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ISO 13095:2014(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 Technical Committee ISO/TC 201, Surface chemical
analysis, Subcommittee SC 9, Scanning probe microscopy.
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ISO 13095:2014(E)

Introduction
Atomic force microscopes (AFMs) are of increasing importance for imaging surfaces at the nanoscale.
The imaging mechanism involves a dilation of the surface form by the AFM probe shape. In practice, the
radii of probe tips are in the range of 1 nm to 200 nm, which is the same order of magnitude as that of
many important surface features. AFM images may, therefore, be strongly affected by the shape and size
of the AFM probe used for imaging. In addition, the mechanism used to control the distance between
the AFM probe and the sample surface can create artefacts in AFM images, because the effective probe
shape characteristic depends on the control parameters. The probe radius and its half-cone angle are
often used for the specification of AFM probes. However, practical probes are often not described so
simply. Therefore, a quantitative expression for probe shank shape is required. This International
Standard describes two methods for the detailed determination of probe shank shape: a projection of
the probe profile (PPP) and the effective probe shape characteristic (EPSC), both of which are projected
onto a defined plane and which, in turn, include the effect of the probe controlling mechanism. The PPP
provides a continuous profile, whereas the EPSC provides a few discrete characteristic points. PPP, used
in conjunction with a probe shape characteristic (PSC) measurement, gives the quality of the probe
for general applications, whereas EPSC indicates the usefulness of the probe for depth measurements
in narrow trenches and similar profiles. The true surface shape can be recovered and estimated from
the measured surface with an accurate model of the true probe shape. This International Standard
provides methods for the quantitative determination of aspects of AFM probe shank shape, to ensure
that the probe is adequate to measure surfaces with narrow trenches and similar profiles and to ensure
reproducible AFM imaging.
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INTERNATIONAL STANDARD ISO 13095:2014(E)
Surface Chemical Analysis — Atomic force microscopy —
Procedure for in situ characterization of AFM probe shank
profile used for nanostructure measurement
1 Scope
This International Standard specifies two methods for characterizing the shape of an AFM probe tip,
specifically the shank and approximate tip profiles. These methods project the profile of an AFM probe
tip onto a given plane, and the characteristics of the probe shank are also projected onto that plane
under defined operating conditions. The latter indicates the usefulness of a given probe for depth
measurements in narrow trenches and similar profiles. This International Standard is applicable to the
probes with radii greater than 5u , where u is the uncertainty of the width of the ridge structure in the
0 0
reference sample used to characterize the probe.
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 18115-2:2010, Surface chemical analysis — Vocabulary — Part 2: Terms used in scanning-probe
microscopy
ISO/TS 80004-4:2011, Nanotechnologies — Vocabulary — Part 4: Nanostructured materials
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115-2, ISO/TS 80004-4 and
the following apply.
NOTE Some of the terms and definitions are reprinted here for convenience.
3.1
aspect ratio of the probe
ratio of the probe profile length at a certain position to the probe profile width at that position
3.2
deflection sensitivity
sensitivity factor converting the output of an AFM optical displacement detection system for a cantilever
in the contact mode to the displacement of the tip
3.3
error signal
feedback control system signal whose amplitude and sign are used to correct the position and/or
alignment between the controlling and the controlled elements
3.4
effective probe shape characteristic
EPSC
relationship between the probe profile width and probe profile length for a given probe, including the
effects of the true probe shape, artefacts due to the feedback controlling mechanism in the AFM modes
employed, and other imaging mechanisms of AFM projected onto a defined plane
Note 1 to entry: The defined plane is usually the x-z plane.
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ISO 13095:2014(E)

3.5
narrow-ridge structure
isolated plateau with thin width having wide gaps on either side
3.6
peak force mode
AFM intermittent contact mode using frequencies well below resonance in which the maximum force is
used for measurement or for imaging
3.7
probe apex
[4]
structure at the extremity of a probe, the apex of which senses the surface
3.8
probe profile width
projected width of a probe at a defined probe profile length, which may be for a defined azimuth or
projection plane
Note 1 to entry: The defined projection plane is usually the x-z plane.
3.9
probe profile length
length, measured from the probe apex along the instrument’s z (vertical)-axis, to a defined point on the
probe axis
3.10
probe shape characteristic
PSC
relationship between the probe profile width and the probe profile length for a given probe projected
onto a defined plane
Note 1 to entry: The defined projection plane is usually the x-z plane.
3.11
projected probe profile
PPP
measured profile of the probe projected onto a defined plane
Note 1 to entry: The defined projection plane is usually the x-z plane.
Note 2 to entry: Figure 1 a) shows schematically the relationship between the probe profile width, w, and length,
l, and b) the definition of the aspect ratio, a.
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ISO 13095:2014(E)

a)
b)
Probeproile
width
Aspect ratio
w
Z
z
y
Y Probe
a = l / w
a=l / w
Probe proile
l
length
x
X
Probeapex
Figure 1 — Probe profile width (w), defined here for projection on the x-z plane, and probe
profile length (l)
4 Symbols and abbreviated terms
In the list of abbreviated terms below, note that the “M” in the abbreviation “AFM,” defined here as
an abbreviation for “Microscopy,” also is used as an abbreviation for “Microscope” depending on the
context. The following are the abbreviated terms.
AFM atomic force microscopy
AM amplitude modulation
EPSC effective probe shape characteristic
CRM certified reference material
PID proportional integral derivative (controller)
PSC probe shape characteristic
PPP projected probe profile
TEM transmission electron microscopy
The following are the symbols for use in the formulae and as abbreviations in the text.
A free oscillation amplitude of the cantilever before approaching the probe to the sample
0
A oscillation amplitude of the cantilever for AFM imaging
sp
a aspect ratio of the probe
D distance between the side wall of an isolated ridge structure and the adjacent wall
0
D line distance between the two side walls of the j trench structure
j th
e maximum error signal, in nanometres, measured during the recording of the probe shape data
m
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ISO 13095:2014(E)

f numbers of the frames
H average depth of the trenches on either side of the ridge structure
0
H depth of the j trench structure
j th
j index number for the j measurement of trench
th
l length of the probe profile
l maximum measured depth for the j trench
j th
L width of the ridge structure
0
m index number for m measurement of the probe profile length
th
n index number for n measurement of the probe profile length
th
p probe profile length at m measurement
m th
p probe profile length at n measurement
n th
q difference of probe profile length between PSC and EPSC data
r corner radius of the reference sample
r corner radius of the ridge structure provided by the CRM supplier
r
r maximum corner radius of the trench structure
t
r corner radius of the side wall of the j trench structure provided by the CRM supplier
j th
s maximum slope of the PSC curve
s maximum slope estimated from the EPSC data
E
u combined standard uncertainty of the measurement of the probe profile length
u standard uncertainty of the width of the ridge structure
0
u standard uncertainty of the random component obtained by the probe profile length measurement
s
u standard uncertainty of the gap width of the multiple-trench structure
t
w projected profile width of the AFM probe in the x-z plane
w’ apparent width of the ridge structure
w measured width of the AFM probe at j measurement
j th
ΔL error in l caused by the presence of a non-zero value of r
r
5 Procedure for probe characterization
5.1 Methods for the determination of AFM probe shapes
There are two methods to determine AFM probe shank profiles:
a) narrow-ridge method to determine the probe projected profile (PPP) and the probe shape
characteristic (PSC);
b) multiple-trench method to determine the effective probe shape characteristic (EPSC) for depth
measurement.
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ISO 13095:2014(E)

Either one or both of the above methods shall be used to determine aspects of the probe shank profile.
Suitable applications for each method are given in Table 1. The approximate profile of an AFM probe
tip, i.e. the profile obtained by removing that of the tip apex, is determined by the narrow-ridge method
using a reference sample. The resulting profile is given as the PPP onto a given plane. The PSC is an
expression of the relationship between the probe profile width and length obtained from PPP. The EPSC
is the PSC determined at a few points using a multiple-trench structure. The narrow-ridge method is
used mainly for the evaluation of AFM measurements for convex nano-structures, i.e. protrusions,
whereas the multiple-trench method, under the two-point contact condition, is mainly used for depth
measurements in narrow trenches and similar profiles. The two methods generate results that differ
to an extent that depends on the measurement conditions, such as humidity and the parameters used
to control the probe during AFM imaging. The appropriate probe characteristic shall be used for the
relevant analysis.
NOTE Examples of PSC and EPSC are shown in Annex A.
Table 1 — Summary of the methods
Subclauses Method Suitable application Properties to be determined
5.2 to 5.4.1, Narrow-ridge method Conventional AFM measurements and i) Projected probe profile (PPP), ii)
5.4.2, 5.5 analysis of protrusions in AFM images Probe shape characteristic (PSC)
5.2 5.4.1, Multiple-trench method Depth measurements, such as those of Effective probe shape characteristic
5.4.3, 5.5 contact holes and trenches (EPSC)
5.2 Reference sample setting
A reference sample with either a ridge structure, suitable trench structures, or both types of structures
is required and is described in Annex B. An example of a reference structure is shown in Annex C. It
is recommended to select a reference sample with a small corner radius and various sets of trench
structures. If the corner radius is large, the uncertainty region at the tip apex increases. The reference
sample shall be set on the sample holder so that the relevant structures are placed either perpendicular
or parallel to the fast raster axis of the AFM scanner, as shown in Figure 2 a) and Figure 2 b). Specifically,
if the probe shape is to be projected onto the plane through the longitudinal direction of the cantilever,
the lines of the pattern in the reference sample and the longitudinal direction of the cantilever shall
be aligned perpendicular to each other, as shown in Figure 2 a) and Figure 2 b) is the complementary
case for characterizing the probe shape projected onto the plane normal to the longitudinal direction
of the cantilever. If instead the probe shape is required for a different specific orientation [for example,
P-Q direction in Figure 2 c)], align the direction of the pattern lines in the reference sample to be
perpendicular to that specified orientation, as shown in Figure 2 c). The reference structures of the
sample should be rigidly fixed onto the specimen holder, and the orientation of the structures of the
reference sample with respect to the fast raster axis of the scanner shall be set within an error of 1° of
perpendicular orientation. When the ambient humidity changes, the effective probe shape often changes
[3]
due to the altered amount of water adsorbed on the probe surface ; thus, humidity shall be recorded.
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ISO 13095:2014(E)

The reference specimen and the cantilever shall be electrically grounded to avoid electrostatic damage
and the accumulation of contaminants collected by electrostatic charge.
a) Perpendicular to the fast b) Perpendicular to the fast c) Perpendicular to a specific
raster axis raster axis direction (P-Q direction) in an
AFM image
Figure 2 — Alignment of the AFM probe to the lines of a pattern in the reference sample
5.3 Requirements of AFM and AFM imaging
The x-, y-, and z-axes of the AFM shall be calibrated for their orthogonality and for the measurement of
[2]
length scales to the accuracy required by the user. The accuracy level should be considered carefully
since this may limit the accuracy with which the probe shape may be defined. The topographic image
and error-signal image shall both be measured and displayed synchronously for monitoring and
optimization of the feedback parameters. The scan length along both x and y-axes should be set to cover
the necessary structures of the reference material. If a closed-loop scanning system is used, the position
noise/lateral noise ratio should be considered to determine the desired resolution. The pixel size should
be chosen so that it is consistent with the desired resolution of <1 nm.
EXAMPLE For a raster width of 1 000 nm, 2 000 pixels per line scan should be used.
At least 10 raster lines shall be measured. The scan rate and other feedback parameters for imaging
shall be optimized to achieve an amplitude error-signal of <1 nm. Other control parameters should be
set to values similar to those that will be used for the actual measurements of the sample of interest,
if possible. Other experimental conditions shall be adjusted by following the instrument manual or
other documented and validated procedures. Such conditions include the alignment of the laser and
detectors, initialization of other hardware, and adjustment of the excitation frequency (for dynamic
mode operation). After setting up the AFM, check the thermal drift in the image. If the thermal drift
[1]
remains, see ISO 11039. The imaging mode of the AFM, such as contact mode, intermittent contact
mode (AM-mode), and others, shall be set to obtain the topographic and error signal images. A common
procedure for setting up the AFM is to adjust the setpoint such that the forward and backward profiles
of the probe match. However, a difference between the PSC and EPSC may remain. In AM mode, by
increasing the free oscillation amplitude, decreasing the operating amplitude (low setpoint), or both,
the difference between PSC and EPSC may be minimized. However, tip-wear increases when high
amplitudes and high setpoints are used. For reducing tip wear, the phase contrast should be maintained
at low levels, without abrupt phase jumps and apparent topographic jumps. If the difference between
PSC and EPSC is reduced, the free oscillation amplitude and setpoints should be adjusted to realize the
maximum apparent depth of the trenches. Another method to reduce the difference between PSC and
EPSC is to use an operating mode that is controlled by cantilever deflection, such as contact mode or
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ISO 13095:2014(E)

peak force mode. If static contact mode is used, then it is recommended to use hopping scanning mode
(a scanning mode in which, at each pixel, the surface is approached with the probe to a setpoint, then the
[5]
height of the probe is recorded at this point and the probe is retracted ). To preserve the shape of the
probe, careful changes of the controlling parameters are required to reduce the difference of the probe
profile width between PSC and EPSC.
NOTE An example of an EPSC measurement, with associated reproducibility, is provided in Annex D.
5.4 Measurement of probe shank profile
5.4.1 General Remarks
A narrow-ridge structure shall be measured for PPP analysis, and a multiple-trench structure shall be
measured for EPSC analysis under two-point contact conditions. The choice of experimental parameters
such as the oscillation amplitude of the cantilever and the setpoints may affect the EPSC measurement
results. These parameters shall be optimized by following the instrumental manual or other documented
and validated procedures. The recommended absolute value of the maximum error signal e is smaller
m
than 1 nm (i.e. | e | < 1 nm). The measured surface plane of the profile of the reference sample shall be
m
as level as possible. The plane correction for probe profile analysis is described in Annex E.
5.4.2 Method using narrow-ridge structure for obtaining PPP and PSC
The reference sample, which includes a narrow-ridge structure with known line width, uncertainty of
line width, and edge radius, shall be obtained. Details of the reference sample are shown in Annex B. The
procedure for determining the PPP and the PSC are given below.
a) Measure the line profile of the narrow-ridge structure along the fast raster axis of the AFM
instrument. The scan length along this axis shall be sufficiently wide such that the depth measured
on either side of the ridge reaches to 90 % of the total depth, H .
0
NOTE If the probe reaches the bottom of the adjacent trenches, spurious wings appear in the probe
shape; hence plotted data are limited to depths up to 0,9 H .
0
b) Plot the measured line profile taking the x-axis as the fast scanning axis and the z-axis as the
measured height. The scale units shall be in nanometres for both axes. The top of the profile,
averaging over the plateau which includes the width of the ridge structure, shall be set on the z-axis
at 0 nm (l = 0 nm), and the maximum scale depth on either side shall be over 0,9 H , as shown in
0
Figure 3 a).
c) Draw two horizontal lines on the plot obtained in step b, as shown in Figure 3 b). One line is at the
z-axis depth of r , where r is the radius of the ridge corner and is determined separately, and the
r r
other line is at the depth of 0,9 H .
0
d) Re-plot the line profile obtained in step b by subtracting the value of the width of the ridge structure
(L ) from the x-axis values for the data for the right hand side of the ridge structure in the height
0
region between r and 0,9 H , as shown in Figure 3 c) and Figure 3 d). Invert this plot as shown in
r 0
Figure 3 e), this provides the PPP.
e) Plot the relationship between the width w (x-axis) and length l (z-axis) of the profile obtained in step
d. Use “probe profile width” as the x-axis label, and “probe profile length” as the z-axis label. The
minimum and maximum values of the z-axis shall be r and 0,9 H , respectively, as shown in Figure 3
r 0
f). This provides the PSC.
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ISO 13095:2014(E)

a) Measured data b) The profile of the ridge c) Subtracting L
O
d) Probe profile after e) Inversion of d) giving the PPP f) PSC
removing the ridge width
Figure 3 — Determination of PPP and PSC using a narrow-ridge structure
5.4.3 Method using multiple-trench structure for obtaining EPSC
A reference sample that includes a multiple-trench structure with different known gap distances and
associated uncertainties shall be obtained. Details of a representative reference sample are shown in
Annex B. The procedure for determining the EPSC is given below.
a) Measure the line profile of the multiple-trench structure along the fast raster axis of the AFM
instrument. The scan length along this axis shall be sufficiently wide so that more than three trench
structures are measured. Confirm that flat regions appear at both sides in each trench profile.
b) Draw a straight line connecting the flat region appearing on either side of the j trench, and measure
th
the maximum depth l from that line, as shown in Figure 4 a).
j
c) Measure the maximum (apparent) depth l for each trench structure. Plot l as a function of the gap
j j
width D , which is included in the data sheet for the reference sample. Label the x-axis as “probe
j
profile width” and the z-axis as “probe profile length.” The units of the x and z-axes shall be in
nanometres, as shown in Figure 4 b) for an example with five trenches.
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ISO 13095:2014(E)

a) Schematic drawing of the probe and the j trench with the trajectory of the probe ape
th
b) EPSC measured from the multiple-trench structure
Figure 4
5.5 Uncertainty of the measurement of the probe shank profile
Divergence from the true shape of the probe can arise due to deviations of the reference sample from
its ideal shape, measurement errors of the instrument, and variation of the contact area due to the
positional relationship between the probe and sample surface. EPSC is affected by contact area, but PSC
is not, because point contact is realized on the narrow-ridge structure. Since sharp AFM tips will wear
with use, and in order to reduce the amount of work needed to obtain PSC (or PPP) and EPSC, a simple
uncertainty estimate is described below.
5.5.1 Uncertainty of the PPP or PSC measurement
The uncertainty of the PPP or PSC measurement of the probe shank profile arises mainly from the
standard uncertainty of the width, u , of the ridge structure, the standard deviation in the error of the
0
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ISO 13095:2014(E)

probe control signal, e , in nanometres, the maximum slope, s, in the PSC curve, and corner radius, r , of
m r
a ridge structure. Calculate the standard uncertainty of the measurement, u , as follows:
s
a) From the image of the selected area containing the ridge structure, select f line scans evenly
distributed through the image where f > 7;
b) Calculate the probe profile leng
...

DRAFT INTERNATIONAL STANDARD ISO/DIS 13095
ISO/TC 201/SC 9 Secretariat: KATS
Voting begins on Voting terminates on

2013-07-23 2013-10-23
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION  •  МЕЖДУНАРОДНАЯ ОРГАНИЗАЦИЯ ПО СТАНДАРТИЗАЦИИ  •  ORGANISATION INTERNATIONALE DE NORMALISATION


Surface Chemical Analysis — Atomic force microscopy —
Procedure for in situ characterization of AFM probe shank
profile used for nanostructure measurement
Analyse chimique des surfaces — Microscopie à balayage de sonde — Procédure pour la caractérisation in
situ des sondes AFM utilisées pour mesurer la nanostructure

ICS 71.040.40









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©  International Organization for Standardization, 2013

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ISO/DIS 13095

COPYRIGHT PROTECTED DOCUMENT


©  ISO 2013
All rights reserved. Unless otherwise specified, 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
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2013 – All rights reserved

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DIS 13095
Contents
Foreword . iv
Introduction . iv
1 Scope . 1
2 Normative reference(s) . 1
3 Terms and definitions . 1
4 Symbols (and abbreviated terms) . 3
5 Procedure for probe characterization . 4
5.1 Methods for the determination of AFM probe shapes . 4
5.2 Reference sample setting . 5
5.3 Requirements of AFM and AFM imaging . 6
5.4 Measurement of probe shank profile . 6
5.4.1 General Remarks . 6
5.4.2 Method using narrow-ridge structure for obtaining PPP and PSC . 6
5.4.3 Method using multiple-trench structure for obtaining EPSC . 8
5.5 Uncertainty of the measurement of the probe shank profile . 8
5.5.1 Uncertainty of the PPP or PSC measurement . 8
5.5.2 Uncertainty of the EPSC measurement . 9
6 Reporting of probe characteristics . 9
Annex A (informative) Dependence of AFM images on measurement mode and settings . 10
A.1 Results of the inter-laboratory test . 10
A.2 Example AFM image for a trench structure: dependence on the amplitude setpoints. 10
Annex B (normative) Reference sample preparation . 12
B.1 Requirements for the reference sample . 12
B.2 Narrow-ridge structure . 12
B.3 Multiple-trench structure . 13
Annex C (informative) Example of a reference structure . 14
C.1 General . 14
Annex D (informative) Results of EPSC measurement repeatability test . 15
D.1 Repeatability of EPSC measurements . 15
Annex E (informative) Plane correction for probe shank profile analysis . 17
Annex F (informative) Example of a report . 18
Bibliography . 20

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DIS 13095
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.
ISO 13095 was prepared by Technical Committee ISO/TC 201, Surface Chemical Analysis, Subcommittee
SC 9, Scanning Probe Microscopy.
This second/third/. edition cancels and replaces the first/second/. edition (), [clause(s) / subclause(s) /
table(s) / figure(s) / annex(es)] of which [has / have] been technically revised.
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Introduction
Atomic force microscopes (AFMs) are of increasing importance for imaging surfaces at the nanoscale. The
imaging mechanism involves a dilation of the surface form by the AFM probe shape. In practice, the radii of
probe tips are in the range of 1 to 200 nm, which is the same order of magnitude as that of many important
surface features. AFM images may, therefore, be strongly affected by the shape of the AFM probe used for
imaging. In addition, the mechanism used to control the distance between the AFM probe and the sample
surface can create artefacts in AFM images, because the probe’s profile depends on the control parameters.
The probe radius and its half-cone angle are often used for the specification of AFM probes. However,
practical probes are often not described so simply. Therefore, a quantitative expression for probe shape is
required. This document describes two methods for the detailed determination of probe shape: a projection of
the probe profile (PPP) and the effective probe shape characteristic (EPSC), both of which are projected onto
a defined plane and which, in turn, include the effect of the probe controlling mechanism. The PPP provides a
continuous profile, whereas the EPSC provides a few discrete characteristic points. PPP, used in conjunction
with a probe shape characteristic (PSC) measurement, gives the quality of the probe for general applications,
whereas EPSC indicates the usefulness of the probe for depth measurements in narrow trenches and similar
profiles. To recover and estimate the true surface shape, the measured surface must be eroded
mathematically by an accurate model of the true probe shape. This International Standard provides methods
for the quantitative determination of aspects of AFM probe shape, to ensure that the probe is adequate to
measure surfaces with high-aspect-ratio structures and to ensure reproducible AFM imaging.


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DIS 13095

Surface Chemical Analysis — Atomic force microscopy —
Procedure for in situ characterization of AFM probe shank
profile used for nanostructure measurement
1 Scope
Thi This International Standard specifies two methods for characterizing the shape of an AFM probe tip,
specifically the shank and approximate tip profiles. These methods project the profile of an AFM probe tip onto
a given plane, and the characteristics of the probe shank are also projected onto that plane under defined
operating conditions. The latter indicates the usefulness of a given probe for depth measurements in narrow
trenches and similar profiles. This International Standard is applicable to the probes with radii greater than 5u ,
0
where u is the uncertainty of the width of the ridge structure in the reference sample used to characterize the
0
probe.

2 Normative reference(s)
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.
ISO18115-2:2010 Surface chemical analysis – Vocabulary – Part 2: Terms used in scanning-probe
microscopy
3 Terms and definitions
For the purposes of this document, the terms and definitions given below from ISO 18115-2:2010 Surface
chemical analysis – Vocabulary – Part 2: Terms used in scanning-probe microscopy apply and are reprinted
here for convenience [1].
3.1
aspect ratio of the probe
ratio of the probe profile length at a certain position to the probe profile width at that position
3.2
deflection sensitivity
sensitivity factor converting the output of an AFM optical displacement detection system for a cantilever in the
contact mode to the displacement of the tip in nanometers
3.3
error signal
feedback control system signal whose amplitude and sign are used to correct the position and/or alignment
between the controlling and the controlled elements
3.4
effective probe shape characteristic (EPSC)
relationship between the probe profile width and probe profile length for a given probe, including the effects of
the true probe shape, artefacts due to the feedback controlling mechanism in the AFM modes employed, and
other imaging mechanisms of AFM projected onto a defined plane
NOTE – the defined plane is usually the x-z plane; see Annex A.
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DIS 13095
3.5
narrow-ridge structure
isolated plateau with thin width having wide gaps on either side
3.6
peak force mode
AFM intermittent contact mode using frequencies well below resonance in which the maximum force is used
for measurement or for imaging
3.7
probe apex
structure at the extremity of a probe; the apex senses the surface [ISO 18115-2, 6.120]
3.8
probe profile width
projected width of a probe at a defined probe profile length, which may be for a defined azimuth or projection
plane
NOTE – the defined projection plane is usually the x-z plane.
3.9
probe profile length
length, measured from the probe apex along the instrument’s z (vertical)-axis, to a defined point on the probe
axis
3.10
probe shape characteristic (PSC)
relationship between the probe profile width and the probe profile length for a given probe projected onto a
defined plane
NOTE – the defined projection plane is usually the x-z plane.
3.11
projected probe profile (PPP)
measured profile of the probe projected onto a defined plane
NOTE – the defined projection plane is usually the x-z plane.
Figure 1 shows schematically the relationship between the probe profile width w and length l (a) and the
definition of the aspect ratio a (b).

(a) (b)
Probe profile
width
Aspect ratio
w
Z
z
y Probe
Y
a = l / w
a=l / w
Probe profile
length l
x
X
Probe apex

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DIS 13095
Figure 1 — The probe profile width (w), defined here for projection on the x-z plane, and probe profile
length (l)
4 Symbols (and abbreviated terms)
In the list of abbreviated terms below, note that the "M" in the abbreviation “AFM,” defined here as an
abbreviation for "Microscopy," also is used as an abbreviation for "Microscope" depending on the context. The
abbreviated terms are:
AFM atomic force microscopy
AM amplitude modulation
EPSC effective probe shape characteristic
CRM certified reference material
PID proportional integral derivative (controller)
PSC probe shape characteristic
PPP projected probe profile
TEM transmission electron microscopy
The symbols for use in the equations and as abbreviations in the text are:
A free oscillation amplitude of the cantilever before approaching the probe to the sample
0
A oscillation amplitude of the cantilever for AFM imaging
sp
a aspect ratio of the probe
D distance between the side wall of an isolated ridge structure and the adjacent wall
0
D line distance between the two side walls of the j trench structure
j th
e maximum error signal, in nanometers, measured during the recording of the probe shape data
m
f numbers of the frames
H average depth of the trenches on either side of the ridge structure
0
H depth of the j trench structure
j th
j index number for the j measurement of trench
th
l length of the probe profile
l maximum measured depth for the j trench
j th
L width of the ridge structure
0
m index number for m measurement of the probe profile length
th
n index number for n measurement of the probe profile length
th
p probe profile length at m measurement
m th
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DIS 13095
p probe profile length at n measurement
n th
q difference of probe profile length between PSC and EPSC data
r corner radius of the reference sample
r corner radius of the ridge structure provided by the CRM supplier
r
r maximum corner radius of the trench structure
t
r corner radius of the side wall of the j trench structure provided by the CRM supplier
j th
s maximum slope of the PSC curve
s maximum slope estimated from the EPSC data
E
u combined standard uncertainty of the measurement of the probe profile length
u standard uncertainty of the width of the ridge structure
0
u standard uncertainty of the random component obtained by the probe profile length measurement
s
u standard uncertainty of the gap width of the multiple-trench structure
t
w projected profile width of the AFM probe in the x-z plane
w’ apparent width of the ridge structure
w measured width of the AFM probe at j measurement
j th
ΔL error in l caused by the presence of a non-zero value of r
r
5 Procedure for probe characterization
5.1 Methods for the determination of AFM probe shapes
There are two methods to determine AFM probe shank profiles:
(a) Narrow-ridge method to determine the probe projected profile (PPP) and the probe shape characteristic
(PSC).
(b) Multiple-trench method to determine the effective probe shape characteristic (EPSC) for depth
measurement.
Either one or both of the above methods shall be used to determine aspects of the probe shank profile.
Suitable applications for each method are given in Table 1. The approximate profile of an AFM probe tip, i.e.,
the profile obtained by removing that of the tip apex, is determined by the narrow-ridge method using a
reference sample. The resulting profile is given as the PPP onto a given plane. The PSC is an expression of
the relationship between the probe profile width and length obtained from PPP. The EPSC is the PSC
determined at a few points using a multiple-trench structure. The narrow-ridge method is used mainly for the
evaluation of AFM measurements for convex nano-structures, i.e. protrusions, whereas the multiple-trench
method under the two-point contact condition is mainly used for depth measurements in narrow trenches and
similar profiles. The two methods generate results that differ to an extent that depends on the measurement
conditions, such as humidity and the parameters used to control the probe during AFM imaging. The
appropriate probe characteristic shall be used for the relevant analysis.
NOTE Examples of PSC and EPSC are shown in Annex D.
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Table 1 — Summary of the methods
Clauses Method Suitable application Properties to be determined
5.2 - 5.4.1, Narrow-ridge method. Conventional AFM measurements i) Projected probe profile (PPP),
5.4.2, 5.5 and analysis of protrusions in ii) Probe shape characteristic
AFM images. (PSC)
5.2 - 5.4.1, Multiple-trench Depth measurements, such as Effective probe shape
5.4.3, 5.5 method. those of contact holes and characteristic (EPSC).
trenches.

5.2 Reference sample setting
A reference sample with either a ridge structure, suitable trench structures, or both types of structures is
required and is described in Annex B. It is recommended to select a reference sample with a smaller corner
radius and various sets of trench structures. If the corner radius is large, the uncertainty region at the tip apex
increases. The reference sample shall be set on the sample holder so that the relevant structures are placed
either perpendicular or parallel to the fast raster axis of the AFM scanner, as shown in Figures 2(a) and 2(b).
Specifically, if the probe shape is to be projected onto the plane through the longitudinal direction of the
cantilever, the lines of the pattern in the reference sample and the longitudinal direction of the cantilever shall
be aligned perpendicular to each other, as shown in Figure 2(a). Figure 2(b) is the complementary case for
characterising the probe shape projected onto the plane normal to the longitudinal direction of the cantilever. If
instead the probe shape is required for a different specific orientation, align the direction of the pattern lines in
the reference sample to be perpendicular to that specified orientation, as shown in Figure 2(c). The reference
sample should be rigidly fixed on the specimen holder, and the orientation of the reference sample with
respect to the fast raster axis of the scanner shall be set within an error of 1º. When the ambient humidity
changes, the effective probe shape often changes due to the altered amount of water adsorbed on the probe
surface [2]; thus, humidity shall be recorded. The reference specimen and the cantilever shall be electrically
grounded to avoid electrostatic damage and the accumulation of contaminants collected by electrostatic
charge.
(a) Perpendicular
(b) Parallel
(c) Specific orientation
Fast raster axis
Fast raster axis
Fast raster axis
Cross-sectional view


Figure 2 — Alignment of the AFM probe to the lines of a pattern in the reference sample
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5.3 Requirements of AFM and AFM imaging
The x-, y-, and z-axes of the AFM shall be calibrated for their orthogonality and for the measurement of length
scales to the accuracy required by the user [3]. The accuracy level should be considered carefully since this
may limit the accuracy with which the probe shape may be defined. The topographic image and error-signal
image shall both be measured and displayed synchronously for monitoring and optimization of the feedback
parameters. The scan length along both x- and y-axes should be set to cover the necessary structures of the
reference material. If a closed-loop scanning system is used, the position noise/lateral noise ratio should be
considered to determine the desired resolution. The pixel size should be chosen so that it is consistent with
the desired resolution of <1 nm.
Example - For a raster width of 1000 nm, 2000 pixels per line scan should be used.
At least 10 raster lines shall be measured. The scan rate and other feedback parameters for imaging shall be
optimized to achieve an amplitude error-signal of <1 nm. Other control parameters should be set to values
similar to those that will be used for the actual measurements of the sample of interest, if possible. If a sharp
or high-aspect-ratio probe is used, it is recommended to start from a relatively slow scan rate, such as 0.1 Hz,
and to increase the number of pixels in order to reduce the possible damage to the probe. Other experimental
conditions shall be adjusted by following the instrument manual or other documented and validated
procedures. Such conditions include the alignment of the laser and detectors, initialization of other hardware,
and adjustment of the excitation frequency (for dynamic mode operation). After setting up the AFM, check that
any thermal drift in the image is acceptable, or allow a longer settling time until it is acceptable. If the thermal
drift remains unacceptable, see ISO 11039 [4]. The imaging mode of the AFM, such as contact mode,
intermittent contact mode (AM-mode), and others, shall be set to obtain the topographic and error signal
images. A common procedure for setting up the AFM is to adjust the setpoint to match the forward and
backward profiles of the probe. However, a difference between the PSC and EPSC may remain. In AM mode,
by increasing the free oscillation amplitude, decreasing the operating amplitude (low setpoint), or both, the
difference between PSC and EPSC may be minimized. However, tip wear increases when high amplitudes
and high setpoints are used. For reducing tip wear, the phase contrast should be maintained at low levels,
without abrupt phase jumps and apparent topographic jumps. If the difference between PSC and EPSC is
reduced, the free oscillation amplitude and setpoints should be adjusted to realize the maximum apparent
depth of the trenches. Another method to reduce the difference between PSC and EPSC is to use an
operating mode that is controlled by cantilever deflection, such as contact mode or peak force mode. If static
contact mode is used, then it is recommended to use hopping scanning mode (a scanning mode in which, at
each pixel, the surface is approached with the probe to a setpoint, then the height of the probe is recorded at
this point and the probe is retracted [5]). To preserve the shape of the probe, careful changes of the
controlling parameters are required to reduce the difference of the probe profile width between PSC and
EPSC.
NOTE An example of an EPSC measurement, with associated reproducibility, is provided in Annex D.
5.4 Measurement of probe shank profile
5.4.1 General Remarks
A narrow-ridge structure shall be measured for PPP analysis, and a multiple-trench structure shall be
measured for EPSC analysis under two-point contact conditions. The choice of experimental parameters such
as the oscillation amplitude of the cantilever and the setpoints may affect the EPSC measurement results.
These parameters shall be optimized by following the instrumental manual or other documented and validated
procedures. The recommended absolute value of the maximum error signal e is smaller than 1 nm (i.e., | e |
m m
< nm). The measured surface plane of the profile of the reference sample shall be as level as possible. The
plane correction for probe profile analysis is described in Annex E.
5.4.2 Method using narrow-ridge structure for obtaining PPP and PSC
The reference sample, which includes a narrow-ridge structure with known line width, uncertainty of line
width, and edge radius, shall be obtained. Details of the reference sample are shown in Annex B. The
procedure for determining the PPP and the PSC are given below.
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DIS 13095
a) Measure the line profile of the narrow-ridge structure along the fast raster axis of the AFM instrument.
The scan length along this axis shall be sufficiently wide that the depth measured on either side of the
ridge reaches to 90% of the total depth, H .
0
NOTE If the probe reaches the bottom of the adjacent trenches, spurious wings appear in the probe shape; hence
plotted data are limited to depths up to 0,9H .
0
b) Plot the measured line profile taking the x-axis as the fast scanning axis and the z-axis as the measured
height. The scale units are nanometers for both axes. The top of the profile, averaging over the plateau
which includes the width of the ridge structure, shall be set on the z-axis at 0 nm (l = 0 nm), and the
maximum scale depth on either side shall be over 0,9H , as shown in Figure 3(a).
0
c) Draw two horizontal profiles on the plot obtained in step 2 from the z-axis depth of r , the separately
r
determined radius of the ridge corner, to the depth 0,9H , as shown in Figure 3(b).
0
d) Re-plot the line profile obtained in step 2 by subtracting the value of the width of the ridge structure (L )
0
from the x-axis values for the data for the right hand side of the ridge structure in the height region
between r and 0,9H , as shown in Figures 3(c) and 3(d). Turn the re-plot upside down as shown in
r 0
Figure 3(e). This provides the PPP.
e) Plot the relationship between the width w (x-axis) and length l (z-axis) of the profile obtained in step 4.
Use “probe profile width” as the x-axis label, and “probe profile length” as the z-axis label. The minimum
and maximum values of the z-axis shall be r and 0,9H , respectively, as shown in Figure 3(f). This
r 0
provides the PSC.

l = 0
0.9 H
0
0.9 H
0
0.9 H
0
0.9 H
0
0.9 H
0
Probe profile width [nm]
l = 0

Figure 3 — Determination of PPP and PSC using a narrow-ridge structure. (a) Measured data. (b) The
profile of the ridge. (c) Subtracting L . (d) Probe profile after removing the ridge width. (e) Inversion of
0
(d) giving the PPP. (f) PSC.
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Probe profile length [nm]

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5.4.3 Method using multiple-trench structure for obtaining EPSC
A reference sample that includes a multiple-trench structure with known gap distances and associated
uncertainties shall be obtained. Details of a representative reference sample are shown in Annex B. The
procedure for determining the EPSC is given below.
a) M Measure the line profile of the multiple-trench structure along the fast raster axis of the AFM
instrument. The scan length along this axis shall be sufficiently wide so that more than three trench
structures are measured. Confirm that flat regions appear at both sides in each trench profile.
b) Draw a straight line connecting the flat region appearing on either side of the j trench, and measure the
th
maximum depth l from that line, as shown in Figure 4(a).
j
c) Measure the maximum (apparent) depth l for each trench structure. Plot l as a function of the gap width
...