ASTM E766-98(2008)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E766 −98(Reapproved 2008)
Standard Practice for
Calibrating the Magnification of a Scanning Electron
Microscope
This standard is issued under the fixed designation E766; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—3.1.2 and 6.9.2 were editorially corrected in June 2008.
1. Scope 2.2 ISO Standard:
ISOGuide30:1992TermsandDefinitionsUsedinConnec-
1.1 This practice covers general procedures necessary for
tion with Reference Materials
the calibration of magnification of scanning electron micro-
scopes. The relationship between true magnification and indi-
3. Terminology
cated magnification is a complicated function of operating
3.1 Definitions:
conditions. Therefore,thispracticemustbeappliedtoeachset
3.1.1 For definitions of metallographic terms used in this
of standard operating conditions to be used.
practice see Terminology E7.
1.2 The values stated in SI units are to be regarded as
3.1.2 The definitions related to statistical analysis of date
standard. No other units of measurement are included in this
appearing in Practice E177, Terminology E456, and Practice
standard.
E691 shall be considered as appropriate to the terms used in
this practice.
1.3 This standard does not purport to address all of the
3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
3.2.1 calibration—the set of operations which establish,
responsibility of the user of this standard to establish appro-
under specified conditions, the relationship between magnifi-
priate safety and health practices and determine the applica-
cation values indicated by the SEM and the corresponding
bility of regulatory limitations prior to use.
magnificationvaluesdeterminedbyexaminationofareference
2. Referenced Documents
material.
2.1 ASTM Standards: 3.2.2 calibration method—a technical procedure for per-
E7Terminology Relating to Metallography forming a calibration.
E29Practice for Using Significant Digits in Test Data to
3.2.3 certified reference material—reference material, ac-
Determine Conformance with Specifications
companied by a certificate, one or more of whose property
E177Practice for Use of the Terms Precision and Bias in
values are certified by a procedure which establishes its
ASTM Test Methods
traceability to an accurate realization of the unit in which the
E456Terminology Relating to Quality and Statistics
property values are expressed, and for which each certified
E691Practice for Conducting an Interlaboratory Study to
value is accompanied by an uncertainty at a stated level of
Determine the Precision of a Test Method
confidence (see ISO Guide 30:1992).
3.2.4 pitch—the separation of two similar structures, mea-
sured as the center to center or edge to edge distance.
This practice is under the jurisdiction ofASTM Committee E04 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray and
3.2.5 reference material—a material or substance one or
Electron Metallography.
more of whose property values are sufficiently homogeneous,
Current edition approved June 15, 2008. Published June 2008. Originally
stable, and well established to be used for the calibration of an
approved in 1980. Last previous edition approved in 2003 E766–98(2003). DOI:
10.1520/E0766-98R08E01.
apparatus, the assessment of a measurement method, or for
See Annex A1.
assigning values to materials (see ISO Guide 30:1992).
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
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E766−98 (2008)
3.2.6 reference standard—a reference material, generally of 5.4.3 Made from materials which provide good contrast for
the highest metrological quality available, from which mea- the various imaging modes, especially secondary electron and
surements are derived. backscatter electron imaging.
5.4.4 Made of or coated with electrically conductive, elec-
3.2.7 traceability—the property of a result of a measure-
tron beam stable materials, and
ment whereby it can be related to appropriate international/
5.4.5 Made of materials which can be cleaned to remove
national standards through an unbroken chain of comparisons.
contamination which occurs during normal use.
3.2.8 verification—confirmation by examination and provi-
5.5 Undertypicalusesomecontaminationofthecalibration
sion of evidence that specified requirements have been met.
specimen should be expected. When cleaning becomes neces-
sary always follow the manufacturer’s instructions. Improper
4. Significance and Use
handling, especially during cleaning, may invalidate the cali-
4.1 Proper use of this practice can yield calibrated magni-
bration specimen’s certificate of accuracy or traceability and
ficationswithprecisionof5%orbetterwithinamagnification
require re-certification. Care should be taken to prevent the
range of from 10 to 50 000X.
standard from sustaining mechanical damage which may alter
4.2 The use of calibration specimens traceable to
the standard’s structure.
international/national standards, such as NIST-SRM 484, with
5.6 The facility using this practice shall have arrangements
this practice will yield magnifications accurate to better than
for the proper storage, handling, and use of the calibration
5% over the calibrated range of operating conditions.
specimen(s) which should include but is not limited to:
4.3 Theaccuracyofthecalibratedmagnifications,ordimen-
5.6.1 Storage in a desiccating cabinet or vacuum container,
sional measurements, will be poorer than the accuracy of the
5.6.2 Usingfingercots,cleanroomglovesortweezerswhen
calibration specimen used with this practice.
handling, and
5.6.3 Restricting its use to calibration only, unless it can be
4.4 For accuracy approaching that of the calibration speci-
shownthattheperformanceofthecalibrationspecimenwillbe
men this practice must be applied with the identical operating
unaffected by such use.
conditions (accelerating voltage, working distance and magni-
fication) used to image the specimens of interest.
5.7 Thefacilityusingthispracticeshallestablishaschedule
for verification of the calibration specimen(s), where verifica-
4.5 It is incumbent upon each facility using this practice to
tion should include but is not limited to:
define the standard range of magnification and operating
5.7.1 Visualandmicroscopicalinspectionforcontamination
conditions as well as the desired accuracy for which this
and deterioration which may affect performance,
practice will be applied. The standard operating conditions
5.7.2 Photomicrographic comparison (and documentation)
must include those parameters which the operator can control
of the present state of the calibration specimen(s) to the
including: accelerating voltage, working distance, magnifica-
original state, and
tion, and imaging mode.
5.7.3 Validation or re-certification of calibration speci-
men(s) distance intervals against other reference standards or
5. Calibration Specimen
certified reference materials.
5.1 Theselectionofcalibrationspecimen(s)isdependenton
the magnification range and the accuracy required.
6. Procedure
5.2 The use of reference standards, reference materials, or
6.1 Mounting of the calibration specimen.
certified reference materials traceable to international/national
6.1.1 Visually inspect the calibration specimen surface for
standards (NIST, Gaithersburg, MD; NPL,Teddington, UK; or
contamination and deterioration which may affect perfor-
JNRLM, Tsukuba, Japan) calibration specimens is recom-
mance.Removeanydustorloosedebrisusingextracarenotto
mended. However, the use of internal or secondary reference
damage the specimen surface. One safe method is to use clean
materials validated against reference standards or certified
dry canned air to remove the loose surface debris.
reference materials may be used with this practice.
6.1.2 Ensure good electrical contact by following the SEM
5.3 Where traceability to international or national standards
and calibration specimen manufacturers’ directions for mount-
is not required, internal reference materials, verified as far as
ing. In some instances the use of a conductive cement may be
technically practicable and economically feasible, are appro-
required.
priate as calibration specimens and may be used with this
6.1.3 Mountthecalibrationspecimenrigidlyandsecurelyin
practice.
the SEM specimen stage to minimize any image degradation
caused by vibration.
5.4 The most useful calibration specimens should have the
following characteristics:
6.2 Evacuate the SEM chamber to the desired or standard
5.4.1 A series of patterns allowing calibration of the full
working vacuum.
field of view as well as fractional portions of the field of view
6.3 Turn OFF the tilt correction and scan rotation circuits.
over the range of standard magnifications. Suitable standards
These circuits should be calibrated independently.
allow for the pattern “pitch” to be measured,
5.4.2 Pitch patterns allowing calibration in both X and Y 6.4 Set the specimen tilt to 0° such that the surface of the
without having to rotate the sample or the raster, calibration specimen is perpendicular to the electron beam. A
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E766−98 (2008)
technique for checking specimen surface perpendicularity is to 6.10.1 Measure with an appropriate ruler and record the
observetheimagefocusasthespecimenistranslatedtwicethe pitchdistance(D)betweentwoofthefiducialmarkings(inmm
picture width in the X or Y direction. The change of image 6 0.5 mm) which are separated by the largest spacing in the
focusshouldbeminimalatanominalmagnificationof1000X. field of view. This step must be carried out for both the X and
Y directions of the view CRT.
6.5 Adjust the accelerating voltage, working distance, and
6.10.1.1 If the fiducial markings are lines the measurement
magnification to the desired or standard operating conditions.
must be made perpendicular to the fiducial lines and from line
6.6 The instrument should be allowed to fully stabilize at
centertolinecenterorlineedgetothecorrespondinglineedge.
the desired operating conditions. The time required will be
6.10.1.2 With some calibration specimens, it may be neces-
pre-determined by the facility using this practice.
sary to rotate the specimen by 90° in order to determine
magnificationinboththeXandYdirections.Ifthisisthecase,
6.7 Minimize residual magnetic hysteresis effects in the
follow 6.10-6.10.2 before rotating the sample. Then follow
lenses by using the degauss feature, cycling lens circuits
6.8.2 and 6.8.3 to re-align the calibration specimen in the new
ON-OFF-ON two or three times, or follow manufacturers
orientation and repeat 6.10 and 6.11.
recommendations.
6.10.2 Calculate the magnification by using 6.12.
6.8 Adjust the image of the calibration specimen on the
6.11 Recording CRT calibration method.
viewing CRT.
6.11.1 Photograph the field used in 6.10 with sufficient
6.8.1 Bringtheimageofthespecimenintosharpfocus.The
signal to noise ratio and image contrast to allow for accurate
sample working distance should be pre-selected to determine
measurements.
magnification accuracy since different working distances may
have different magnification errors. The specimen height (Z 6.11.2 Allowsufficienttimeforthephotographicmaterialto
axis)isthenadjustedtoattainfocusontheviewingCRT.Ifthe stabilize prior to measurement. This will minimize the effects
SEM has a digital working distance display, the desired value of dimensional changes in the film caused by temperature and
may be selected by adjusting the objective lens focus. humidity.
6.8.2 Mechanically rotate the calibration specimen so the 6.11.3 Measure and record the pitch distance (D) between
measurement pattern(s) is parallel to the X or Y directions of two of the fiducial markings (in mm 6 0.5 mm) which are
the CRT, or both. Never use the scan rotation circuits to rotate separatedbythelargestspacinginthephotomicrographforthe
the image since the circuit may introduce distortions or best precision.
magnification error, or both.
6.11.4 Itisrecommendedthatthefiducialmarkingsusedfor
6.8.3 Translate the calibration specimens so the fiducial thepitchmeasurementbeatleast10mmfromthephotoedges
markings of the measurement pattern(s) span 90% of the full to minimize edge distortion effects.
display of the viewing CRT using the SEM specimen stage X
6.11.5 If the measurement pattern consists of lines which
andYcontrols.Itisdesirabletoseebothedgesofeachfiducial
span the length or width of the photomicrograph, then repeat
marking in order to ascertain the line-center or repeated pitch
the measurement in 6.11.3 at least three times at locations
distance on the calibration specimen
separated by at least 3 mm so that the average spacing may be
6.8.4 A ruler of known accuracy should be used for these determined (see Fig. 1).
measurements.
6.11.6 Calculate the magnification for each measurement
using 6.12. When multiple measurements have been made
6.9 Viewing CRT“micrometer” marker calibration method.
determine the mean and standard deviation for the set of
NOTE 1—This measurement determines the micrometer marker accu- measurements.
racy on the CRT for the indicated magnification (which is assumed to be
6.12 Calculation of Magnification:
correct), and not the magnification accuracy. Often the viewing CRT is a
differentsizethantherecordCRTandresultantmicrograph.Thedisplayed
6.12.1 Calculate the true magnification (M) by dividing the
magnification of the viewing CRT may therefore be incorrect as it was
measured distance (D), usually in mm, by the accepted,
probably intended for the final image.
certified, or `known’ spacing (CS), usually in micrometers and
6.9.1 Measure the length of the “micrometer” marker (in
then multiplying by the appropriate length units conversion
mm 6 0.5mm) with an appropriate ruler of known accuracy.
factor (CF). Conversion factors do not have to be used if the
Record this value (D) and the indicated magnification. Due to
same units in the calculation are used. For instance, if the
the thickness of the CRT face plate be careful that parallax
magnified pitch distance is measured in mm, divide that
errors in the measurement do not affect
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