ASTM E766-98(2003)
(Practice)Standard Practice for Calibrating the Magnification of a Scanning Electron Microscope
Standard Practice for Calibrating the Magnification of a Scanning Electron Microscope
SIGNIFICANCE AND USE
Proper use of this practice can yield calibrated magnifications with precision of 5 % or better within a magnification range of from 10 to 50 000X.
The use of calibration specimens traceable to international/national standards, such as NIST-SRM 484, with this practice will yield magnifications accurate to better than 5 % over the calibrated range of operating conditions.
The accuracy of the calibrated magnifications, or dimensional measurements, will be poorer than the accuracy of the calibration specimen used with this practice.
For accuracy approaching that of the calibration specimen this practice must be applied with the identical operating conditions (accelerating voltage, working distance and magnification) used to image the specimens of interest.
It is incumbent upon each facility using this practice to define the standard range of magnification and operating conditions as well as the desired accuracy for which this practice will be applied. The standard operating conditions must include those parameters which the operator can control including: accelerating voltage, working distance, magnification, and imaging mode.
SCOPE
1.1 This practice covers general procedures necessary for the calibration of magnification of scanning electron microscopes. The relationship between true magnification and indicated magnification is a complicated function of operating conditions. Therefore, this practice must be applied to each set of standard operating conditions to be used.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E 766 – 98 (Reapproved 2003)
Standard Practice for
Calibrating the Magnification of a Scanning Electron
Microscope
This standard is issued under the fixed designation E 766; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This practice covers general procedures necessary for 3.1 Definitions:
the calibration of magnification of scanning electron micro- 3.1.1 For definitions of metallographic terms used in this
scopes. The relationship between true magnification and indi- practice see Terminology E 7.
cated magnification is a complicated function of operating 3.1.2 The definitions related to statistical analysis of date
conditions. Therefore,thispracticemustbeappliedtoeachset appearing in Practice E 77, Terminology E 456, and Practice
of standard operating conditions to be used. E 691 shall be considered as appropriate to the terms used in
1.2 The values stated in SI units are to be regarded as the this practice.
standard. 3.2 Definitions of Terms Specific to This Standard:
1.3 This standard does not purport to address all of the 3.2.1 calibration—the set of operations which establish,
safety concerns, if any, associated with its use. It is the under specified conditions, the relationship between magnifi-
responsibility of the user of this standard to establish appro- cation values indicated by the SEM and the corresponding
priate safety and health practices and determine the applica- magnification values determined by examination of a reference
bility of regulatory limitations prior to use. material.
3.2.2 calibration method—a technical procedure for per-
2. Referenced Documents
forming a calibration.
2.1 ASTM Standards:
3.2.3 certified reference material—reference material, ac-
E 7 Terminology Relating to Metallography companied by a certificate, one or more of whose property
E 29 Standard Practice For Using Significant Digits in Test
values are certified by a procedure which establishes its
Data to Determine Conformance with Specifications
traceability to an accurate realization of the unit in which the
E 177 Practice for Use of the Terms Precision and Bias in property values are expressed, and for which each certified
ASTM Test Methods
value is accompanied by an uncertainty at a stated level of
E 456 Terminology Relating to Quality and Statistics confidence (see ISO Guide 30:1992).
E 691 Practice for Conducting an Interlaboratory Study to
3.2.4 pitch—the separation of two similar structures, mea-
Determine the Precision of a Test Method sured as the center to center or edge to edge distance.
2.2 ISO Standard:
3.2.5 reference material—a material or substance one or
ISO Guide 30: 1992 Terms and Definitions Used in Con- more of whose property values are sufficiently homogeneous,
nection with Reference Materials
stable, and well established to be used for the calibration of an
apparatus, the assessment of a measurement method, or for
assigning values to materials (see ISO Guide 30:1992).
This practice is under the jurisdiction of ASTM Committee E04 on Metallog-
3.2.6 reference standard—a reference material, generally of
raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray and
Electron Metallography. the highest metrological quality available, from which mea-
Current edition approved Nov. 1, 2003. Published December 2003. Originally
surements are derived.
approved in 1980. Last previous edition approved in 1998 E 766 – 98.
3.2.7 traceability—the property of a result of a measure-
See Annex A1.
ment whereby it can be related to appropriate international/
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
national standards through an unbroken chain of comparisons.
Standards volume information, refer to the standard’s Document Summary page on
3.2.8 verification—confirmation by examination and provi-
the ASTM website.
4 sion of evidence that specified requirements have been met.
Available from American National Standards Institute, 25 W. 43rd St., 4th
Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 766 – 98 (2003)
4. Significance and Use require re-certification. Care should be taken to prevent the
standard from sustaining mechanical damage which may alter
4.1 Proper use of this practice can yield calibrated magni-
the standard’s structure.
fications with precision of 5 % or better within a magnification
5.6 The facility using this practice shall have arrangements
range of from 10 to 50 000X.
for the proper storage, handling, and use of the calibration
4.2 The use of calibration specimens traceable to
specimen(s) which should include but is not limited to:
international/national standards, such as NIST-SRM 484, with
5.6.1 Storage in a desiccating cabinet or vacuum container,
this practice will yield magnifications accurate to better than
5.6.2 Usingfingercots,cleanroomglovesortweezerswhen
5 % over the calibrated range of operating conditions.
handling, and
4.3 Theaccuracyofthecalibratedmagnifications,ordimen-
5.6.3 Restricting its use to calibration only, unless it can be
sional measurements, will be poorer than the accuracy of the
shown that the performance of the calibration specimen will be
calibration specimen used with this practice.
unaffected by such use.
4.4 For accuracy approaching that of the calibration speci-
5.7 The facility using this practice shall establish a schedule
men this practice must be applied with the identical operating
for verification of the calibration specimen(s), where verifica-
conditions (accelerating voltage, working distance and magni-
tion should include but is not limited to:
fication) used to image the specimens of interest.
5.7.1 Visualandmicroscopicalinspectionforcontamination
4.5 It is incumbent upon each facility using this practice to
and deterioration which may affect performance,
define the standard range of magnification and operating
5.7.2 Photomicrographic comparison (and documentation)
conditions as well as the desired accuracy for which this
of the present state of the calibration specimen(s) to the
practice will be applied. The standard operating conditions
original state, and
must include those parameters which the operator can control
5.7.3 Validation or re-certification of calibration speci-
including: accelerating voltage, working distance, magnifica-
men(s) distance intervals against other reference standards or
tion, and imaging mode.
certified reference materials.
5. Calibration Specimen
6. Procedure
5.1 Theselectionofcalibrationspecimen(s)isdependenton
6.1 Mounting of the calibration specimen.
the magnification range and the accuracy required.
6.1.1 Visually inspect the calibration specimen surface for
5.2 The use of reference standards, reference materials, or
contamination and deterioration which may affect perfor-
certified reference materials traceable to international/national
mance.Removeanydustorloosedebrisusingextracarenotto
standards (NIST, Gaithersburg, MD; NPL, Teddington, UK; or
damage the specimen surface. One safe method is to use clean
JNRLM, Tsukuba, Japan) calibration specimens is recom-
dry canned air to remove the loose surface debris.
mended. However, the use of internal or secondary reference
6.1.2 Ensure good electrical contact by following the SEM
materials validated against reference standards or certified
and calibration specimen manufacturers’ directions for mount-
reference materials may be used with this practice.
ing. In some instances the use of a conductive cement may be
5.3 Where traceability to international or national standards
required.
is not required, internal reference materials, verified as far as
6.1.3 Mountthecalibrationspecimenrigidlyandsecurelyin
technically practicable and economically feasible, are appro-
the SEM specimen stage to minimize any image degradation
priate as calibration specimens and may be used with this
caused by vibration.
practice.
6.2 Evacuate the SEM chamber to the desired or standard
5.4 The most useful calibration specimens should have the
working vacuum.
following characteristics:
6.3 Turn OFF the tilt correction and scan rotation circuits.
5.4.1 A series of patterns allowing calibration of the full
These circuits should be calibrated independently.
field of view as well as fractional portions of the field of view
6.4 Set the specimen tilt to 0° such that the surface of the
over the range of standard magnifications. Suitable standards
calibration specimen is perpendicular to the electron beam. A
allow for the pattern “pitch” to be measured,
technique for checking specimen surface perpendicularity is to
5.4.2 Pitch patterns allowing calibration in both X and Y
observe the image focus as the specimen is translated twice the
without having to rotate the sample or the raster,
picture width in the X or Y direction. The change of image
5.4.3 Made from materials which provide good contrast for
focus should be minimal at a nominal magnification of 1000X.
the various imaging modes, especially secondary electron and
6.5 Adjust the accelerating voltage, working distance, and
backscatter electron imaging.
magnification to the desired or standard operating conditions.
5.4.4 Made of or coated with electrically conductive, elec- 6.6 The instrument should be allowed to fully stabilize at
tron beam stable materials, and
the desired operating conditions. The time required will be
5.4.5 Made of materials which can be cleaned to remove pre-determined by the facility using this practice.
contamination which occurs during normal use.
6.7 Minimize residual magnetic hysteresis effects in the
5.5 Under typical use some contamination of the calibration lenses by using the degauss feature, cycling lens circuits
specimen should be expected. When cleaning becomes neces- ON-OFF-ON two or three times, or follow manufacturers
sary always follow the manufacturer’s instructions. Improper recommendations.
handling, especially during cleaning, may invalidate the cali- 6.8 Adjust the image of the calibration specimen on the
bration specimen’s certificate of accuracy or traceability and viewing CRT.
E 766 – 98 (2003)
6.8.1 Bring the image of the specimen into sharp focus.The 6.11.1 Photograph the field used in 6.10 with sufficient
sample working distance should be pre-selected to determine signal to noise ratio and image contrast to allow for accurate
measurements.
magnification accuracy since different working distances may
have different magnification errors. The specimen height (Z 6.11.2 Allowsufficienttimeforthephotographicmaterialto
stabilize prior to measurement. This will minimize the effects
axis) is then adjusted to attain focus on the viewing CRT. If the
of dimensional changes in the film caused by temperature and
SEM has a digital working distance display, the desired value
humidity.
may be selected by adjusting the objective lens focus.
6.11.3 Measure and record the pitch distance (D) between
6.8.2 Mechanically rotate the calibration specimen so the
two of the fiducial markings (in mm 6 0.5 mm) which are
measurement pattern(s) is parallel to the X or Y directions of
separated by the largest spacing in the photomicrograph for the
the CRT, or both. Never use the scan rotation circuits to rotate
best precision.
the image since the circuit may introduce distortions or
6.11.4 Itisrecommendedthatthefiducialmarkingsusedfor
magnification error, or both.
the pitch measurement be at least 10 mm from the photo edges
6.8.3 Translate the calibration specimens so the fiducial
to minimize edge distortion effects.
markings of the measurement pattern(s) span 90 % of the full
6.11.5 If the measurement pattern consists of lines which
display of the viewing CRT using the SEM specimen stage X
span the length or width of the photomicrograph, then repeat
andYcontrols. It is desirable to see both edges of each fiducial
the measurement in 6.11.3 at least three times at locations
marking in order to ascertain the line-center or repeated pitch
separated by at least 3 mm so that the average spacing may be
distance on the calibration specimen
determined (see Fig. 1).
6.8.4 A ruler of known accuracy should be used for these
6.11.6 Calculate the magnification for each measurement
measurements.
using 6.12. When multiple measurements have been made
6.9 Viewing CRT “micron” marker calibration method.
determine the mean and standard deviation for the set of
measurements.
NOTE 1—This measurement determines the micron marker accuracy on
6.12 Calculation of Magnification:
the CRT for the indicated magnification (which is assumed to be correct),
6.12.1 Calculate the true magnification (M) by dividing the
and not the magnification accuracy. Often the viewing CRT is a different
measured distance (D), usually in mm, by the accepted,
size than the record CRT and resultant micrograph. The displayed
magnification of the viewing CRT may therefore be incorrect as it was certified, or 8known’ spacing (CS), usually in micrometers and
probably intended for the final image.
then multiplying by the appropriate length units conversion
factor (CF). Conversion factors do not have to be used if the
6.9.1 Measure the length of the “micron” marker (in mm 6
same units in the calculation are used. For instance, if the
0.5mm) with an appropriate ruler of known accuracy. Record
magnified pitch distance is measured in mm, divide that
this value (D) and the indicated magnification. Due to the
thickness of the CRT face plate be careful that parallax errors
in the measurement do not affect the accuracy.
6.9.2 Calculate the true micron marker size by multiplying
the indicated magnification by the displayed micron marker
length. Calculate the percentage error by diving these two
values.Iferrorismorethantheallowabletolerance,themicron
marker should be adjusted. This may be accomplished by the
manufacturer of the SEM or by following the manufacturer’s
documented procedures.
6.10 Viewing CRT Calibration Method:
6.10.1 Measure with an appropriate ruler and record the
pitchdistance(D)betweentwoofthefiducialmarkings(inmm
6 0.5 mm) which are separated by the largest spacing in the
field of view. This step must be carried out for both the X and
Y directions of the view CRT.
6.10.1.1 If the fiducial markings are lines the measurement
must be made perpendicular to the fiducial lines and from line
centertolinecenterorlineedgetothecorrespondinglineedge.
NOTE 1—A 4 3 5 in. ( mm)
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.