ASTM E986-04(2017) Standard Practice for Scanning Electron Microscope Beam Size Characterization.pdf

1、Designation: E986 04 (Reapproved 2017)Standard Practice forScanning Electron Microscope Beam Size Characterization1This standard is issued under the fixed designation E986; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o

2、f last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides a reproducible means by whichone aspect of the performance of a scanning electron micro-scope

3、 (SEM) may be characterized. The resolution of an SEMdepends on many factors, some of which are electron beamvoltage and current, lens aberrations, contrast in the specimen,and operator-instrument-material interaction. However, theresolution for any set of conditions is limited by the size of theele

4、ctron beam. This size can be quantified through the mea-surement of an effective apparent edge sharpness for a numberof materials, two of which are suggested. This practice requiresan SEM with the capability to perform line-scan traces, forexample, Y-deflection waveform generation, for the suggested

5、materials. The range of SEM magnification at which thispractice is of utility is from 1000 to 50 000 . Highermagnifications may be attempted, but difficulty in makingprecise measurements can be expected.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with

6、its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.3 This international standard was developed in accor-dance with internationally recognized principles on stand

7、ard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E7 Terminology Relating to MetallographyE766 P

8、ractice for Calibrating the Magnification of a Scan-ning Electron Microscope3. Terminology3.1 Definitions: For definitions of terms used in thispractice, see Terminology E7.3.2 Definitions of Terms Specific to This Standard:3.2.1 Y-deflection waveformthe trace on a CRT resultingfrom modulating the C

9、RT with the output of the electrondetector. Contrast in the electron signal is displayed as achange in Y (vertical) rather than brightness on the screen. Thisoperating method is often called Y-modulation.4. Significance and Use4.1 The traditional resolution test of the SEM requires, as afirst step,

10、a photomicrograph of a fine particulate sample takenat a high magnification. The operator is required to measure adistance on the photomicrograph between two adjacent, butseparate edges. These edges are usually less than one millime-tre apart. Their image quality is often less than optimumlimited by

11、 the S/N ratio of a beam with such a small diameterand low current. Operator judgment is dependent on theindividual acuity of the person making the measurement andcan vary significantly.4.2 Use of this practice results in SEM electron beam sizecharacterization which is significantly more reproducibl

12、e thanthe traditional resolution test using a fine particulate sample.5. Suggested Materials5.1 SEM resolution performance as measured using theprocedure specified in this practice will depend on the materialused; hence, only comparisons using the same material havemeaning. There are a number of cri

13、teria for a suitable materialto be used in this practice. Through an evaluation of thesecriteria, two samples have been suggested. These samples arenonmagnetic; no surface preparation or coating is required;thus, the samples have long-term structural stability. Thesample-electron beam interaction sh

14、ould produce a sharplyrising signal without inflections as the beam scans across theedge. Two such samples are:5.1.1 Carbon fibers, NISTSRM 2069B.35.1.2 Fracture edge of a thin silicon wafer, cleaved on a(111) plane.1This practice is under the jurisdiction of ASTM Committee E04 on Metallog-raphy and

15、 is the direct responsibility of Subcommittee E04.11 on X-Ray andElectron Metallography.Current edition approved June 1, 2017. Published June 2017. Originallyapproved in 1984. Last previous edition approved in 2010 as E986 04(2010). DOI:10.1520/E0986-04R17.2For referenced ASTM standards, visit the A

16、STM 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.3Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaither

17、sburg, MD 20899-1070, http:/www.nist.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision

18、on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.16. Procedure6.1 Inspect the specimen for cleanliness. If the specimenappears contaminated, a new sample is recommended as anycle

19、aning may adversely affect the quality of the specimen edge.6.2 Ensure good electrical contact with the specimen byusing a conductive cement to hold the specimen on a SEMstub, or by clamping the specimen on the stage of the SEM.Mount the specimen rigidly in the SEM to minimize any imagedegradation c

20、aused by vibration.6.3 Verify magnification calibration for both X and Y direc-tions. This can be accomplished by using Practice E766.6.4 Use a clean vacuum of 1.33 by 102Pa (104mm Hg)or better to minimize specimen contamination resulting fromelectron beam and residual hydrocarbons interacting durin

21、gexamination. The presence of a contamination layer has adeleterious effect on image-edge quality.6.5 Allow a minimum of 30 min for stabilization of elec-tronic components, vacuum stability, and thermal equilibriumfor the electron gun and lenses. The selection of optimum SEMparameters is at the disc

22、retion of the operator.4For measuringthe ultimate resolution, these will typically be: high kV(30max.), short working distance (5 to 10 mm), smallest spotsize, and long scan time.6.6 Any alternative set of conditions can be used to measureprobe size, but they will measure beam diameter under thosesp

23、ecific conditions, not ultimate resolution.NOTE 1The performance measurement must be repeated for each kVsetting used.6.7 Saturate the filament and check both filament and gunalignment for any necessary adjustment. Allow time for stabi-lization.6.8 Set all lens currents at a resettable value with th

24、e aid ofa suitable digital voltmeter, if available and allow time forstabilization.6.9 Cycle lens circuits OFF-ON two to three times tominimize hysteresis effects. An alternate procedure may beused to drive the lens through a hysteresis loopincreasecurrent above operating current, decrease below ope

25、ratingcurrent, then back up to operating current.6.10 Adjust lens apertures and stigmator for optimum reso-lution (minimum astigmatism). Because of its higherresolution, the secondary electron imaging mode is mostcommonly used. This procedure may also be used to charac-terize SEM performance in the

26、backscattered electron imagingmode.6.11 Locate a field on the chosen specimen that shows thedesired edge detail. (See Fig. 1.) Avoid tilting the stage sincethis will change the magnification due to image foreshortening.6.12 Select the highest magnification that is sufficient toallow critical focusin

27、g of the image and shows image-edgetransition from white to black contrast (for example, fuzziness) of at least 5-mm horizontal width in the photographed image.6.13 Rotate the specimen, not the scan, and shift the field ofview on the specimen so that the desired edge is orientedperpendicular to the

28、horizontal scan direction near the center ofthe CRT.6.14 Make sure that no gamma or derivative processing isemployed.6.15 Obtain a line-trace photograph across the desired edgeusing a recording time of at least 60 s. (See Fig. 2.)6.15.1 CautionSlow scan rates in the line-trace modemay cause burning

29、of the CRT-screen phosphor for improperlyadjusted analog SEM-CRT screens.4Newbury, D. E., “Imaging Strategy for the SEMA Tutorial,” SEM, Vol. 1,1981, pp. 7178.FIG. 1 Edge of Graphitized Natural Cellulose Fiber Used to Pro-duce Line Traces (Fig. 3)FIG. 2 Typical Waveform With 20 and 80 % Contrast Lev

30、els Illus-tratedE986 04 (2017)26.16 Locate the maximum and minimum Y-axis deflectionsacross the edge of the specimen in the line-trace photograph.(See Fig. 2.)6.17 The difference between these values is the full-edgecontrast produced in the line trace. From this contrast value,compute the Y-axis pos

31、itions that correspond to contrast levelsof 20 and 80 % of the full-contrast value.20% level 5 0.2 3 max2 min!1min(1)80% level 5 0.8 3 max2 min!1min(2)6.17.1 These levels are illustrated schematically on Fig. 2.Locate these positions in the line-trace photograph and mea-sure the horizontal distance

32、(D) in mm on the photographbetween these points. The slope of the line trace should have aratio (Y/D) of 2 to 4. The distance (D) should range between 2to 4 mm. The performance parameter (P), expressed innanometres, is then defined as follows:P 5 D 3106!/M (3)where M is the SEM calculated and correc

33、ted magnificationusing an acceptable standard.6.18 Photograph the field selected for later reference to aidin the location of the image edge used for the performancemeasurement.6.19 Repeat the line-trace photograph and measurementprocess outlined in 6.15 through 6.17 at two additional edges inthe ma

34、terial studied. Three waveform traces using a graphite-fiber edge are shown in Fig. 3.6.20 Average the three results to produce the performanceparameter (P).P 5 P11P21P3!#/3 (4)7. Precision and Bias7.1 At the present time, it is not possible to give a specificvalue for the precision and bias of the

35、performance test basedon extensive experience. However, the sources of error andtheir best estimates of uncertainties at a SEM magnification of80 to 50 000 under controlled operating conditions and withexperienced operators, are as follows:Source Uncertainty, %SEM magnification (M) 10Measurement var

36、iation betweenoperators2Measurement of waveform (D)2Approximate overall uncertainty 117.2 Another source of uncertainty arises from edge effectsincluding transmission of electrons through the edge of thespecimen when the beam diameter is very small.8. Reproducibility8.1 Reproducibility of the perfor

37、mance parameter may bedetermined by repeating the steps in Section 6 at intervalsdetermined by the users requirements. Measurement of per-formance is recommended after repair or realignment of theelectron optical functions or after major changes in instrument-operating parameters, for example, beam

38、voltage or lenssettings, or both. A listing of instrument parameters thatinfluence the performance is included in the Annex of PracticeE766.9. Keywords9.1 electron beam size; E766; graphite fiber; magnification;NISTSRM 2069B; resolution; SEM; SEM performance; spotsize; waveformASTM International tak

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41、sed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at th

42、e address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (ph

43、one), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 3 Set of Waveforms Measured to Determine PerformanceParameter (P) (Eq 1)E986 04 (2017)3