1、Designation: E766 141Standard Practice forCalibrating the Magnification of a Scanning ElectronMicroscope1This standard is issued under the fixed designation E766; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTENote 1 in Figure 1 was editorially corrected in May 2016.1. Scope1.1 This practice covers general procedures necessary forthe calibra
3、tion of magnification of scanning electron micro-scopes. The relationship between true magnification and indi-cated magnification is a complicated function of operatingconditions.2Therefore, this practice must be applied to each setof standard operating conditions to be used.1.2 The values stated in
4、 SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and heal
5、th practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E7 Terminology Relating to MetallographyE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE177 Practice for Use of the Terms
6、 Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and StatisticsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Standard:ISO Guide 30: 1992 Terms and Definitions Used in Connec-tion with Reference Materials43. Terminol
7、ogy3.1 Definitions:3.1.1 For definitions of metallographic terms used in thispractice see Terminology E7.3.1.2 The definitions related to statistical analysis of dateappearing in Practice E177, Terminology E456, and PracticeE691 shall be considered as appropriate to the terms used inthis practice.3.
8、2 Definitions of Terms Specific to This Standard:3.2.1 calibrationthe set of operations which establish,under specified conditions, the relationship between magnifi-cation values indicated by the SEM and the correspondingmagnification values determined by examination of a referencematerial.3.2.2 cal
9、ibration methoda technical procedure for per-forming a calibration.3.2.3 certified reference materialreference material, ac-companied by a certificate, one or more of whose propertyvalues are certified by a procedure which establishes itstraceability to an accurate realization of the unit in which t
10、heproperty values are expressed, and for which each certifiedvalue is accompanied by an uncertainty at a stated level ofconfidence (see ISO Guide 30:1992).3.2.4 pitchthe separation of two similar structures, mea-sured as the center to center or edge to edge distance.3.2.5 reference materiala materia
11、l or substance one ormore of whose property values are sufficiently homogeneous,stable, and well established to be used for the calibration of anapparatus, the assessment of a measurement method, or forassigning values to materials (see ISO Guide 30:1992).1This practice is under the jurisdiction of
12、ASTM Committee E04 on Metallog-raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray andElectron Metallography.Current edition approved Jan. 1, 2014. Published March 2014. Originallyapproved in 1980. Last previous edition approved in 2008 as E766 98(2008)1.DOI: 10.1520/E0766-14.2See
13、 Annex A1.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institu
14、te (ANSI), 25 W. 43rd St.,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 States13.2.6 reference standarda reference material, generally ofthe highest metrological quality available, from whi
15、ch mea-surements are derived.3.2.7 traceabilitythe property of a result of a measure-ment whereby it can be related to appropriate international/national standards through an unbroken chain of comparisons.3.2.8 verificationconfirmation by examination and provi-sion of evidence that specified require
16、ments have been met.4. Significance and Use4.1 Proper use of this practice can yield calibrated magni-fications with precision of 5 % or better within a magnificationrange of from 10 to 50 000X.4.2 The use of calibration specimens traceable tointernational/national standards, such as NIST-SRM 484, w
17、iththis practice will yield magnifications accurate to better than5 % over the calibrated range of operating conditions.4.3 The accuracy of the calibrated magnifications, or dimen-sional measurements, will be poorer than the accuracy of thecalibration specimen used with this practice.4.4 For accurac
18、y approaching that of the calibration speci-men this practice must be applied with the identical operatingconditions (accelerating voltage, working distance and magni-fication) used to image the specimens of interest.4.5 It is incumbent upon each facility using this practice todefine the standard ra
19、nge of magnification and operatingconditions as well as the desired accuracy for which thispractice will be applied. The standard operating conditionsmust include those parameters which the operator can controlincluding: accelerating voltage, working distance,magnification, and imaging mode.5. Calib
20、ration Specimen5.1 The selection of calibration specimen(s) is dependent onthe magnification range and the accuracy required.5.2 The use of reference standards, reference materials, orcertified reference materials traceable to international/nationalstandards (NIST, Gaithersburg, MD; NPL, Teddington,
21、 UK; orJNRLM, Tsukuba, Japan) calibration specimens is recom-mended. However, the use of internal or secondary referencematerials validated against reference standards or certifiedreference materials may be used with this practice.5.3 Where traceability to international or national standardsis not r
22、equired, internal reference materials, verified as far astechnically practicable and economically feasible, are appro-priate as calibration specimens and may be used with thispractice.5.4 The most useful calibration specimens should have thefollowing characteristics:5.4.1 A series of patterns allowi
23、ng calibration of the fullfield of view as well as fractional portions of the field of viewover the range of standard magnifications. Suitable standardsallow for the pattern “pitch” to be measured,5.4.2 Pitch patterns allowing calibration in both X and Ywithout having to rotate the sample or the ras
24、ter,5.4.3 Made from materials which provide good contrast forthe various imaging modes, especially secondary electron andbackscatter electron imaging.5.4.4 Made of or coated with electrically conductive, elec-tron beam stable materials, and5.4.5 Made of materials which can be cleaned to removecontam
25、ination which occurs during normal use.5.5 Under typical use some contamination of the calibrationspecimen should be expected. When cleaning becomes neces-sary always follow the manufacturers instructions. Improperhandling, especially during cleaning, may invalidate the cali-bration specimens certif
26、icate of accuracy or traceability andrequire re-certification. Care should be taken to prevent thestandard from sustaining mechanical damage which may alterthe standards structure.5.6 The facility using this practice shall have arrangementsfor the proper storage, handling, and use of the calibration
27、specimen(s) which should include but is not limited to:5.6.1 Storage in a desiccating cabinet or vacuum container,5.6.2 Using finger cots, clean room gloves or tweezers whenhandling, and5.6.3 Restricting its use to calibration only, unless it can beshown that the performance of the calibration speci
28、men will beunaffected by such use.5.7 The facility using this practice shall establish a schedulefor verification of the calibration specimen(s), where verifica-tion should include but is not limited to:5.7.1 Visual and microscopical inspection for contaminationand deterioration which may affect per
29、formance,5.7.2 Photomicrographic comparison (and documentation)of the present state of the calibration specimen(s) to theoriginal state, and5.7.3 Validation or re-certification of calibration speci-men(s) distance intervals against other reference standards orcertified reference materials.6. Procedu
30、re6.1 Mounting of the calibration specimen.6.1.1 Visually inspect the calibration specimen surface forcontamination and deterioration which may affect perfor-mance. Remove any dust or loose debris using extra care not todamage the specimen surface. One safe method is to use cleandry canned air to re
31、move the loose surface debris.6.1.2 Ensure good electrical contact by following the SEMand calibration specimen manufacturers directions for mount-ing. In some instances the use of a conductive cement may berequired.6.1.3 Mount the calibration specimen rigidly and securely inthe SEM specimen stage t
32、o minimize any image degradationcaused by vibration.6.2 Evacuate the SEM chamber to the desired or standardworking vacuum.6.3 Turn OFF the tilt correction and scan rotation circuits.These circuits should be calibrated independently.6.4 Set the specimen tilt to 0 such that the surface of thecalibrati
33、on specimen is perpendicular to the electron beam. AE766 1412technique for checking specimen surface perpendicularity is toobserve the image focus as the specimen is translated twice thepicture width in the X or Y direction. The change of imagefocus should be minimal at a nominal magnification of 10
34、00X.6.5 Adjust the accelerating voltage, working distance, andmagnification to the desired or standard operating conditions.6.6 The instrument should be allowed to fully stabilize atthe desired operating conditions. The time required will bepre-determined by the facility using this practice.6.7 Mini
35、mize residual magnetic hysteresis effects in thelenses by using the degauss feature, cycling lens circuitsON-OFF-ON two or three times, or follow manufacturersrecommendations.6.8 Adjust the image of the calibration specimen on theviewing display.6.8.1 Bring the image of the specimen into sharp focus
36、. Thesample working distance should be pre-selected to determinemagnification accuracy since different working distances mayhave different magnification errors. The specimen height (Zaxis) is then adjusted to attain focus on the viewing display. Ifthe SEM has a digital working distance display, the
37、desiredvalue may be selected by adjusting the objective lens focus.6.8.2 Mechanically rotate the calibration specimen so themeasurement pattern(s) is parallel to the X or Y directions ofthe image display, or both. Never use the scan rotation circuitsto rotate the image since the circuit may introduc
38、e distortionsor magnification error, or both.6.8.3 Translate the calibration specimens so the fiducialmarkings of the measurement pattern(s) span 90 % of the fulldisplay of the viewing display using the SEM specimen stageX and Y controls. It is desirable to see both edges of eachfiducial marking in
39、order to ascertain the line-center orrepeated pitch distance on the calibration specimen6.9 Digital image calibration:6.9.1 Follow the manufacturers calibration instructions bychoosing two points or drawing a line between the centers oredges of the repeating structure on the calibration specimen.Ent
40、er the known distance into the SEM imaging software andsave a calibration file for each set of conditions as themanufacturer provides. The content of the calibration file is adistance per pixel value that varies with digital resolution aswell as microscope conditions.6.10 Analog Image Display Calibr
41、ation Method:6.10.1 Measure with an appropriate ruler and record thepitch distance (D) between two of the fiducial markings (in mm6 0.5 mm) which are separated by the largest spacing in thefield of view. This step must be carried out for both the X andY directions of the image display.6.10.1.1 If th
42、e fiducial markings are lines the measurementmust be made perpendicular to the fiducial lines and from linecenter to line center or line edge to the corresponding line edge.6.10.1.2 With some calibration specimens, it may be neces-sary to rotate the specimen by 90 in order to determinemagnification
43、in both the X andYdirections. If this is the case,follow 6.10 6.10.2 before rotating the sample. Then follow6.8.2 and 6.8.3 to re-align the calibration specimen in the neworientation and repeat 6.10 and 6.11.6.10.2 Calculate the magnification by using 6.12.6.11 Recording CRT calibration method (for
44、older SEMs).6.11.1 Photograph the field used in 6.10 with sufficientsignal to noise ratio and image contrast to allow for accuratemeasurements.6.11.2 Allow sufficient time for the photographic material tostabilize prior to measurement. This will minimize the effectsof dimensional changes in the film
45、 caused by temperature andhumidity.6.11.3 Measure and record the pitch distance (D) betweentwo of the fiducial markings (in mm 6 0.5 mm) which areseparated by the largest spacing in the photomicrograph for thebest precision.6.11.4 It is recommended that the fiducial markings used forthe pitch measur
46、ement be at least 10 mm from the photo edgesto minimize edge distortion effects.6.11.5 If the measurement pattern consists of lines whichspan the length or width of the photomicrograph, then repeatthe measurement in 6.11.3 at least three times at locationsseparated by at least 3 mm so that the avera
47、ge spacing may bedetermined (see Fig. 1).6.11.6 Calculate the magnification for each measurementusing 6.12. When multiple measurements have been madedetermine the mean and standard deviation for the set ofmeasurements.6.12 Calculation of Magnification:6.12.1 Calculate the true magnification (M) by d
48、ividing themeasured distance (D), usually in mm, by the accepted,certified, or known spacing (CS), usually in micrometers andNOTE 1A4 5 in. (101.6 127 mm) photomicrograph of a referencematerial, a 10 m pitch square grid imposed on a silicon wafer, used as acalibration specimen. This calibration spec
49、imen is not certified. Thismicrograph was obtained using 3 kVaccelerating voltage, 26 mm workingdistance, and a magnification setting of 700X. Measurements of D (in mm6 0.5 mm) in both the horizontal and vertical directions are madeapproximately 10mm from the edges of the micrograph and in the center.In this example the horizontal magnification is 620X (6 2X) and thevertical magnification is 627X (6 3X).FIG. 1 Photomicrograph of a Reference MaterialE766 1413then multiplying by the appropriate length units conversionfactor (CF). Conversion factors do
