1、Designation: E 986 04Standard Practice forScanning Electron Microscope Beam Size Characterization1This standard is issued under the fixed designation E 986; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 (SEM) may be c
3、haracterized. 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 theelectron beam. Thi
4、s 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 suggestedmaterials. The
5、range of SEM magnification at which thispractice is of utility is from 1000 to 50 000 3 . 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 its use. It i
6、s 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.2. Referenced Documents2.1 ASTM Standards:2E 7 Terminology Relating to MetallographyE 766 Practice for Calibrating the Magnif
7、ication of a Scan-ning Electron Microscope3. Terminology3.1 Definitions: For definitions of terms used in this prac-tice, see Terminology E 7.3.2 Definitions of Terms Specific to This Standard:3.2.1 Y-deflection waveformthe trace on a CRT resultingfrom modulating the CRT with the output of the elect
8、rondetector. 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, a photomicrograph of a fine par
9、ticulate 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 the S/N ratio of a beam with s
10、uch 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 reproducible thanthe traditional resolutio
11、n 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 criteria for a suitable materialto
12、 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 should produce a sharplyrising si
13、gnal 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.6. Procedure6.1 Inspect the specimen for cleanliness. If the specimenappears contaminated, a new sample is recommen
14、ded as anycleaning 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 SEM1This practice is under the jurisdiction of ASTM Committee E04 on Metallog-raphy and is the direct responsibility of
15、Subcommittee E04.11 on X-Ray andElectron Metallography.Current edition approved July 1, 2004. Published July 2004. Originally approvedin 1984. Last previous edition approved in 1997 as E 986 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at s
16、erviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from National National Institute of Standards and Technology,Gaithersburg, MD 20899.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
17、Conshohocken, PA 19428-2959, United States.stub, or by clamping the specimen on the stage of the SEM.Mount the specimen rigidly in the SEM to minimize any imagedegradation caused by vibration.6.3 Verify magnification calibration for both X and Y direc-tions. This can be accomplished by using Practic
18、e E 766.6.4 Use a clean vacuum of 1.33 by 102Pa (104mm Hg)or better to minimize specimen contamination resulting fromelectron beam and residual hydrocarbons interacting duringexamination. The presence of a contamination layer has adeleterious effect on image-edge quality.6.5 Allow a minimum of 30 mi
19、n for stabilization of elec-tronic components, vacuum stability, and thermal equilibriumfor the electron gun and lenses. The selection of optimum SEMparameters is at the discretion of the operator.4For measuringthe ultimate resolution, these will typically be: high kV(30max.), short working distance
20、 (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 thosespecific conditions, not ultimate resolution.NOTE 1The performance measurement must be repeated for each kVsetting used.6.7 Satu
21、rate 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 the aid ofa suitable digital voltmeter, if available and allow time forstabilization.6.9 Cycle lens circuits OFF-ON two to three
22、 times tominimize hysteresis effects. An alternate procedure may beused to drive the lens through a hysteresis loopincreasecurrent above operating current, decrease below operatingcurrent, then back up to operating current.6.10 Adjust lens apertures and stigmator for optimum reso-lution (minimum ast
23、igmatism). Because of its higher resolu-tion, the secondary electron imaging mode is most commonlyused. This procedure may also be used to characterize SEMperformance in the backscattered electron imaging mode.6.11 Locate a field on the chosen specimen that shows thedesired edge detail. (See Fig. 1.
24、) Avoid tilting the stage sincethis will change the magnification due to image foreshortening.6.12 Select the highest magnification that is sufficient toallow critical focusing of the image and shows image-edgetransition from white to black contrast (for example, fuzziness)of at least 5-mm horizonta
25、l 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 horizontal scan direction near the center ofthe CRT.6.14 Make sure that no gamma or derivative processing isemployed.6.15 Obta
26、in 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 of the CRT-screen phosphor for improperlyadjusted analog SEM-CRT screens.6.16 Locate the maximum and minimum Y-axis deflection
27、sacross 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 positions that correspond to contrast levelsof 20 and 80 % of the full-contrast value.2
28、0 % level 5 0.2 3 gmax2gmin! 1gmin(1)80 % level 5 0.8 3 gmax2gmin! 1gmin(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 (D) in mm on the photograph4Newbury, D. E., “Imaging Strategy for the SEMA T
29、utorial,” SEM, Vol. 1,1981, pp. 7178.FIG. 1 Edge of Graphitized Natural Cellulose Fiber Used toProduce Line Traces (Fig. 3)FIG. 2 Typical Waveform With 20 and 80 % Contrast LevelsIllustratedE986042between these points. The slope of the line trace should have aratio (Y/D) of 2 to 4. The distance (D)
30、should range between 2to 4 mm. The performance parameter (P), expressed innanometres, is then defined as follows:P 5 D 3 106!/M (3)where M is the SEM calculated and corrected magnificationusing an acceptable standard.6.18 Photograph the field selected for later reference to aidin the location of the
31、 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 material studied. Three waveform traces using a graphite-fiber edge are shown in Fig. 3.6.20 Average the three results to produce t
32、he performanceparameter (P).P 5 P11 P21 P3!#/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 performance test basedon extensive experience. However, the sources of error andtheir best estimates of uncertainties at a SEM
33、magnification of80 to 50 000 3 under controlled operating conditions and withexperienced operators, are as follows:Source Uncertainty, %SEM magnification (M) 610Measurement variation betweenoperators62Measurement of waveform (D) 62Approximate overall uncertainty 117.2 Another source of uncertainty a
34、rises from edge effectsincluding transmission of electrons through the edge of thespecimen when the beam diameter is very small.8. Reproducibility8.1 Reproducibility of the performance parameter may bedetermined by repeating the steps in Section 6 at intervalsdetermined by the users requirements. Me
35、asurement of per-formance is recommended after repair or realignment of theelectron optical functions or after major changes in instrument-operating parameters, for example, beam voltage or lenssettings, or both. A listing of instrument parameters thatinfluence the performance is included in the Ann
36、ex of PracticeE 766.9. Keywords9.1 electron beam size; E766; graphite fiber; magnification;NISTSRM 2069B; resolution; SEM; SEM performance; spotsize; waveformASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standa
37、rd. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewe
38、d every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible
39、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 the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh
40、ohocken, 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 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).FIG. 3 Set of Waveforms Measured to Determine PerformanceParameter (P) (Eq 1)E986043
