1、Designation: E 983 05Standard Guide forMinimizing Unwanted Electron Beam Effects in AugerElectron Spectroscopy1This standard is issued under the fixed designation E 983; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.Note Changes were made throughout and the year date changed on July 25, 2005.1. Scope1.1 This guide outlines the origins and manif
3、estations ofunwanted electron beam effects inAuger electron spectroscopy(AES).1.2 Some general guidelines are provided concerning theelectron beam parameters which are most likely to producethese effects and suggestions are offered on how to minimizethem.1.3 General classes of materials are identifi
4、ed which aremost likely to exhibit unwanted electron beam effects. Inaddition, a tabulation of some specific materials which havebeen observed to undergo electron damage effects is provided.1.4 A simple method is outlined for establishing the exist-ence and extent of these effects during routine AES
5、 analysis.1.5 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 health practices and determine the applica-bility of regulatory limitations prior to use.2. Re
6、ferenced Documents2.1 ASTM Standards:2E 673 Terminology Relating to Surface AnalysisE 996 Practice for Reporting Data in Auger Electron Spec-troscopy and X-Ray Photoelectron Spectroscopy3. Terminology3.1 See Terminology E 673 for terms used inAuger electronspectroscopy.NOTE 1Electron beam effects an
7、d their consequences are widelyreferred to in the literature using any one or more of the following terms:electron beam damage, sample damage, specimen damage, beam effects,electron beam induced processes, and electron irradiation effects.4. Significance and Use4.1 When electron beam excitation is u
8、sed in AES, theincident electron beam can interact with the specimen materialcausing physical and chemical changes. In general, theseeffects are a hindrance to AES analysis because they causelocalized specimen modification (1, 2, 3, 4).34.2 With specimens that have poor electrical conductivitythe el
9、ectron beam can stimulate the development of localizedcharge on the specimen surface. This effect is a hindrance toAES analysis because the potentials associated with the chargecan either adversely affect the integrity of Auger data or makeAuger data collection difficult.5. Origins of Electron Beam
10、Effects5.1 Electron beam effects in AES may originate from one ormore distinct processes.5.1.1 Charge accumulation (5) (see Chapter 9) in materialswith poor electrical conductivity leading to potentials thatcause distortion of Auger data or make AES data collectiondifficult by virtue of:5.1.1.1 Auge
11、r peak shift on energy scale.5.1.1.2 Auger peak shape and size distortion.5.1.1.3 Auger signal strength instability.5.1.2 Electronic excitation of surface, subsurface, and bulkatoms and molecules leading to specimen changes (6-8) whichinclude:5.1.2.1 Dissociation.5.1.2.2 Electron stimulated desorpti
12、on (ESD) (9).5.1.2.3 Electron stimulated adsorption (ESA) (10).5.1.2.4 Polymerization (11, 12).5.1.2.5 Carburization (13-15).5.1.2.6 Oxidation (16, 17).5.1.2.7 Reduction (18).5.1.2.8 Decomposition (19, 20).1This guide is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the dire
13、ct responsibility of Subcommittee E42.03 on Auger ElectronSpectroscopy and XPS.Current edition approved July 25, 2005. Published July 2005. Originallyapproved in 1984. Last previous edition approved in 2004 as E 983 04.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
14、STM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the references listed at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor
15、Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.2.9 Erosion.5.1.2.10 Diffusion.5.1.3 Charge accumulation in materials of poor electricalconductivity leading to specimen changes which include (21,22, 5) (see Chapter 8):5.1.3.1 Electric field enhanced diffusion.5.1.3.2 Electrom
16、igration (4) (see p. 62).5.1.4 Heating which may cause:5.1.4.1 Annealing.5.1.4.2 Segregation.5.1.4.3 Volatilization.5.1.4.4 Chemical reaction.6. Practical Manifestations of Electron Beam Effects6.1 Electron dose dependent changes in the intensity, en-ergy, peak shape of one or more Auger transitions
17、; dependingupon the material, these changes may be complete within afraction of a second or they may progress for hours.6.2 Discoloration of the specimen at the electron beamirradiated region.6.3 Physical damage to the specimen such as erosion,cracking, blistering, or densification.6.4 Pressure rise
18、s in the analytical vacuum chamber duringelectron irradiation.6.5 Localized electric charge dependent changes in theintensity, energy, or peak shape of all Auger transitions. Thesechanges may be stable but often are erratic resulting in unstableAES signals which may preclude AES data collection.7. E
19、lectron Beam Parameters7.1 Electron Dose and Current Density:7.1.1 Electron dose and current density were previouslydefined using units of C/cm2and mA/cm2, respectively. Theseunits are not consistent with the SI system. To keep fromchanging the magnitude of the numbers appearing in theliterature (fr
20、om which Table 1 is adapted), the multipliers of theterms are being changed. A dose of C/cm2is equivalent to104C/m2, while 1mA/cm2is equivalent to 10A/m2.7.1.2 Specimen material modification can often be related tothe electron dose (D); that is, the number of electrons incidenton a unit area of the
21、specimen, expressed in coulombs persquare centimeter (C/cm2) (1).7.1.3 A number of materials, (for example, see Table 1),exhibit dose-dependent effects when the electron dose exceedsa material specific critical dose Dc. The magnitude of thecritical dose corresponds to the onset of detectable damage
22、andthe values may be subject to future revision. The materialspecific dose, Dcmay be as low as 10A/m2.7.1.4 In practice, the electron dose is directly dependentupon the electron beam current density, JB, (A/m2), the time ofelectron irradiation in seconds, t (s); and the angle of incidence,Q, of the
23、beam on the sample. That is, DC(C/m2)=JB(A/m2)t(s)cosQ. Putting the electron beam current density into com-monly used condition, 10 A/m2would be equivalent to using10-8A incident beam current into a 33 m electron beamdiameter at normal incidence.7.1.5 The electron beam-induced heating of a given mat
24、erialof poor thermal conductivity and the accumulation of chargeon a material of poor electrical conductivity are dependentupon the electron beam current density.7.1.6 Current densities for a static electron beam should beof the order 104A/m2or less for susceptible materials. In thecase of rastered
25、or gated electron beams, the time-averagedcurrent density and the instantaneous current density must beconsidered. Even though the time-averaged current densitymay be small, the instantaneous current density may besufficient to cause specimen damage or specimen charging.7.1.7 In small-spotAES analys
26、is, or scanningAuger micros-copy, the use of electron probes with high current density isinherent. Obviously a trade-off between signal-to-noise and theperturbing effects of the electron beam is required (2).7.2 Electron Energy:7.2.1 The electron beam effects which involve electronicexcitation are n
27、ot strong functions of electron beam energiesused for AES (1 to 25 keV). Changes in electron beam energywill affect the depth, and therefore the volume, in which suchchanges occur.7.2.2 Electron beam effects arising due to charging andelectric fields in the surface can be minimized by appropriateemp
28、irical choices of electron beam condition (acceleratingvoltage, current, and current density). It should be noted thatthe electron beam angle of incidence (the angle between theelectron beam and the specimen normal, as defined in Termi-nology E 673) influences the electron emission coefficient ofthe
29、 specimen surface.8. Susceptible Materials8.1 Nonmetallic Materials, particularly oxides, fluorides,chlorides, alkali halides, carbonates, and organics are mostprone to decomposition under electron beam irradiation.8.2 Adsorbed Species, particularly carbonaceous molecules,water and halogens, are usu
30、ally desorbed, but in some casesmay change their chemical form.8.3 Metal Surfaces (Clean), (23) are most susceptible toESA; the degree is, of course, enhanced by poor vacuumTABLE 1 Electron Beam Damage in AESAMaterialEnergy,keV104C/m2T = time at 110A/m2RefsSi3N42 stable . (24)Al2O35103h(2)Cu, FePtha
31、locyanines1 1 15 min (25)SiO22 0.6 10 min (24)Li2WO41 0.05 8 min (26)NaF, LiF 0.1 0.06 60 s (20)LiNO3, LiSO410.55 (26)KCl 1.5 0.03 30 s (20)TeO220.22 (27)H2O(F) 1.5 0.01 10 s (28)Native oxides 5 2 3 1032s (3)C6H12(F) 0.1 3 3 1040.3 s (29)Na3AlF631041030.1 s (30)CH3OH(F) 1.5 2.5 3 1040.3 s (28)Awhere
32、:Dc= critical dose for detectable damage,T = time of electron bombardment at 10A/m2without detectable damage,andF = frozen.(Adapted from Ref. 1.)E983052conditions and depends on the composition of residual gases.The type of specimen surface preparation is also an importantfactor.8.4 Insulators, may
33、undergo “unstable charging” wherein itis difficult to acquire an AES spectrum.8.5 Mobile Ionic Species, particularly within oxides, ni-trides, and other dielectric materials, are subject to electric fieldinduced migration under the electron beam.8.6 Nonmetallic Powders, fibers, and other specimen co
34、n-figurations which make poor thermal contact with the specimenholder, are more susceptible to beam heating.8.7 Table 1 is a list of some specific materials reported toundergo electron beam induced decomposition duringAES.Anestimate of the critical electron dose, Dc(C/cm2), is included asa guide to
35、the electron beam current density and irradiationtime which can be tolerated without detectable damage.9. Methods of Observation and Minimization9.1 Determine the existence and extent of electron beameffects for unfamiliar specimens by sequential acquisition ofAuger spectra during continuous electro
36、n irradiation. However,if the change occurs within the acquisition time it will not beseen.9.2 If the specimen is a bulk insulator with a smoothsurface, charging is generally reduced by decreasing theelectron beam current, the current density (by defocusing theelectron beam), lowering the accelerati
37、ng voltage, and increas-ing the tilt angle (to increased electron emission). If the surfaceis rough, increased tilt angle may not help since the averageangle between the electron beam and specimen will notchange.9.3 If the specimen is a thin insulating film on a conductivesubstrate, charging is gene
38、rally reduced by increasing theaccelerating voltage and decreasing the angle of incidence.This has the effect of increasing the depth of penetration of theelectron beam into the conductive layer.9.4 Many electron beam effects involving diffusion pro-cesses may be minimized by cooling the specimen. T
39、his can beachieved using a variety of methods including the use of liquidnitrogen cooled specimen holders. Maintain good thermalcontact between the specimen and specimen holder.9.5 For the analysis of insulators, maximize thermal andelectrical contact to the specimen. Consider placing a groundedcond
40、ucting foil or a conductive mask over the specimen nearthe analyzed region or a grid over the specimen surface toassist in charge dissipation. Consider the use of glancingincidence for the electron probe. If the insulating layer is thinconsider using a higher energy electron probe.10. Reporting Elec
41、tron Beam Effects10.1 The conditions that are used to control electron beameffects should be reported in a manner consistent with PracticeE 996. This record should, at a minimum, include the electronbeam conditions, such as accelerating voltage, incident current,current density, time of exposure, an
42、d incidence angle. If theelectron beam was rastered over the specimen, state the rasterspeed, area, and beam diameter. Also, state if any thermalcooling or electrical contact to the specimen was used.11. Keywords11.1 Auger electron spectroscopy; charging; electron beam;electron beam damageREFERENCES
43、(1) Pantano, C. G. and Madey, T. E., “Electron Beam Damage in AugerElectron Spectroscopy,” Applications of Surface Science, Vol 7, 1981,pp. 115141.(2) van Oostrom, A., “Some Aspects of Auger Microanalysis,” SurfaceScience, Vol 89, 1979, pp. 615634.(3) Coad, J. P., Gettings, M., and Rivire, J. C., “B
44、eam Effects in AESRevealed by XPS,” Discussions of the Faraday Society, Vol 60, 1975,pp. 269278.(4) Czanderna, A., Madey, T., and Powell, C., Beam Effects, SurfaceTopography, and Depth Profiling in Surface Analysis, Plenum Press,New York, 1998, pp. 3996.(5) Briggs, D., and Grant, J., Surface Analysi
45、s by Auger and X-rayPhotoelectron Spectroscopy, IM Publications, West Sussex, UK,Chapters 8 and 9.(6) Field, F. H., and Franklin, J. L., Electron Impact Phenomena Rev. Ed.,Academic Press, New York, 1970; Mosiewiksch, B. L., and Smith, S.J., “Electron Impact Excitation at Atoms,” Review of Modern Phy
46、sics,Vol 40 (1968) p. 1.(7) Menzel, D. “Desorption Methods,” in Topics in Applied Physics,R.Gomer, Ed., Vol 4, Springer-Verlag, Berlin, 1975, p. 101.(8) Lehman, C., Interaction of Radiation with Solids and ElementaryDefect Production, North-Holland, Amsterdam, 1977.(9) Musket, R. G. and Ferrante, J.
47、, “Auger Electron Spectroscopy Study ofElectron Impact Desorption,” Surface Science, Vol 21, 1970, pp.440442.(10) Coad, J. P., Bishop, H. E., and Rivire, J. C., “Electron-BeamAssisted Adsorption on the Si (111) Surface,” Surface Science,Vol21, 1970, pp. 253264.(11) Thompson, L. F., and Kerwin, R. E.
48、, “Polymer Resistivity Systemsfor Photo- and Electron Lithography,” Annual Review of MaterialsScience, Vol 6 (1976) p. 267.(12) Thompson, L. F., Stillwagon, L. E., and Doerries, F. M., “NegativeElectron Resists for Direct Fabrication of Devices,” Journal ofVacuum Science and Technology, Vol 15 (1978
49、) p. 938.(13) Madden, H. H., and Ertl, G., “Decomposition of Carbon Monoxideon a (110) Nickel Surface,” Surface Science, Vol 35, 1973, pp.211226.(14) Martinez, J. M., and Hudson, J. B., “The Absorption and Decompo-sition of CO on Pt (111),” Journal of Vacuum Science and Technol-ogy, Vol 10, 1973, pp. 3538.(15) Mathieu, H. H., Mathieu, J. B., McClure, D. E., and Landolt, D.,“Beam Effects in Auger Electron Spectroscopy Analysis of TitaniumOxide Films,” Journal of Vacuum Science and Technology, Vol 14,1977, pp. 10231028.(16) Joyce, B. A., and Neave, J. H., “Electron
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