1、Designation: E983 10Standard Guide forMinimizing Unwanted Electron Beam Effects in AugerElectron Spectroscopy1This standard is issued under the fixed designation E983; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las
2、t 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 guide outlines the origins and manifestations ofunwanted electron beam effects inAuger electron spectroscopy(AES).1.
3、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 identified which aremost likely to exhibit unwanted electron beam effects. Inaddition, a
4、 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 analysis.1.5 The values stated in SI units are to be regarded asstandard. No ot
5、her units of measurement are included in thisstandard.1.6 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
6、of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E673 Terminology Relating to Surface AnalysisE996 Practice for Reporting Data in Auger Electron Spec-troscopy and X-ray Photoelectron Spectroscopy3. Terminology3.1 See Terminology E673 for terms used in Auger electrons
7、pectroscopy.NOTE 1Electron beam effects and 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
8、 Use4.1 When electron beam excitation is used 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 (1-4).34.2 With specimens that have
9、 poor electrical conductivitythe electron 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 dif
10、ficult (5, 6).5. Origins of Electron Beam Effects5.1 Electron beam effects in AES may originate from one ormore distinct processes.5.1.1 Charge accumulation (7) (see Chapter 9) in materialswith poor electrical conductivity leading to potentials thatcause distortion of Auger data or make AES data col
11、lectiondifficult by virtue of:5.1.1.1 Auger peak shift on energy scale,5.1.1.2 Auger peak shape and size distortion, and5.1.1.3 Auger signal strength instability.5.1.2 Electronic excitation of surface, subsurface, and bulkatoms and molecules leading to specimen changes (8-10)which include:5.1.2.1 Di
12、ssociation,5.1.2.2 Electron stimulated desorption (ESD) (11),5.1.2.3 Electron stimulated adsorption (ESA) (12),5.1.2.4 Polymerization (13, 14),5.1.2.5 Carburization (15-17),5.1.2.6 Oxidation (18, 19),5.1.2.7 Reduction (20),5.1.2.8 Decomposition (21, 22),5.1.2.9 Erosion, and5.1.2.10 Diffusion.1This g
13、uide is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.03 on Auger ElectronSpectroscopy and X-Ray Photoelectron Spectroscopy.Current edition approved Nov. 1, 2010. Published December 2010. Originallyapproved in 1984. Last previous
14、 edition approved in 2005 as E983 05. DOI:10.1520/E0983-10.2For 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.3T
15、he boldface numbers in parentheses refer to the references listed at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.3 Charge accumulation in materials of poor electricalconductivity leading to specimen ch
16、anges which include (23,24, 7) (see Chapter 8):5.1.3.1 Electric field enhanced diffusion, and5.1.3.2 Electromigration (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, and5.1.4.4 Chemical reaction.6. Practical Manifestations of Electron Beam
17、Effects6.1 Electron dose dependent changes in the intensity, en-ergy, or peak shape of one or more Auger transitions, or anycombination thereof; depending upon the material, thesechanges may be complete within a fraction of a second or theymay progress for hours.6.2 Discoloration of the specimen in
18、the proximity of theelectron beam irradiated region.6.3 Physical damage to the specimen such as erosion,cracking, blistering, or densification.6.4 Pressure rises in the analytical vacuum chamber duringelectron irradiation.6.5 Localized electric charge dependent changes in theintensity, energy, or pe
19、ak shape of all Auger transitions, or anycombination thereof. These changes may be stable but oftenare erratic resulting in unstable AES signals which maypreclude AES data collection.7. Electron Beam Parameters7.1 Electron Dose and Current Density:7.1.1 Electron dose and current density were previou
20、slydefined 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 (from which Table 1 is adapted), the multipliers of theterms are being changed. A dose of C/cm2is equivalent to104C/
21、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 specimen, expressed in coulombs persquare centimeter (C/cm2) (1).7.1.3 A number of materials, (for example, see T
22、able 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 andthe values may be subject to future revision. The materialspecific critical dose, Dc, may be as low as 1 C/m2
23、.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 beam on the sample. That is, DC(C/m2)=JB(A/m2)t(s)cosQ. Using a typical electron beam current density
24、,10 A/m2would be equivalent to using 10-8A incident beamcurrent into a 33 m electron beam diameter at normalincidence.7.1.5 The electron beam-induced heating of a given materialof poor thermal conductivity and the accumulation of chargeon a material of poor electrical conductivity are dependentupon
25、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 or gated electron beams, the time-averagedcurrent density and the instantaneous current density must beconsidered. Even though t
26、he 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 analysis, or scanningAuger micros-copy, the use of electron probes with high current density isinherent. Obviously a trade-off between
27、 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 not strong functions of electron beam energiesused for AES (1 keV to 25 keV). Changes in electron beamenergy will affect the dept
28、h, and therefore the volume, in whichsuch changes occur.7.2.2 Electron beam effects arising due to charging andelectric fields at the surface can be minimized by appropriateempirical choices of the electron beam condition (acceleratingvoltage, current, and current density). It should be noted thatth
29、e electron beam angle of incidence (the angle between theelectron beam and the specimen normal, as defined in Termi-nology E673) influences the electron emission coefficient ofthe specimen surface and beam penetration depth.8. Susceptible Materials8.1 Nonmetallic Materials, particularly oxides, fluo
30、rides,chlorides, alkali halides, carbonates, and organics are mostprone to decomposition under electron beam irradiation.TABLE 1 Electron Beam Damage in AESAMaterialIncidentBeamEnergy,keVDc,104C/m2T RefsSi3N42 stable . (26)Al2O35103h(2)Cu, FePthalocyanines1 1 15 min (27)SiO22 0.6 10 min (26)Li2WO41
31、0.05 8 min (28)NaF, LiF 0.1 0.06 60 s (22)LiNO3, LiSO410.55 (28)KCl 1.5 0.03 30 s (22)TeO220.22 (29)H2O(F) 1.5 0.01 10 s (30)Native oxides 5 2 3 1032s (3)C6H12(F) 0.1 3 3 1040.3 s (31)Na3AlF631041030.1 s (32)CH3OH(F) 1.5 2.5 3 1040.3 s (30)Awhere:Dc= critical dose for detectable damage,T = time of e
32、lectron bombardment at 10A/m2without detectable damage,andF = frozen.(Adapted from Ref. 1.)E983 1028.2 Adsorbed Species, particularly carbonaceous molecules,water and halogens, are usually desorbed, but in some casesmay change their chemical form.8.3 Metal Surfaces (Clean) (25) are most susceptible
33、toESA; the degree is, of course, enhanced by poor vacuumconditions and depends on the composition of residual gases.The type of specimen surface preparation is also an importantfactor.8.4 Insulators may undergo “unstable charging” wherein itis difficult to acquire an AES spectrum.8.5 Mobile Ionic Sp
34、ecies, 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 con-figurations which make poor thermal contact with the specimenholder, are more susceptible to be
35、am 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 the electron beam current density and irradiationtime which can be tolerated without detectable d
36、amage.9. Methods of Observation and Minimization9.1 Determine the existence and extent of electron beameffects for unfamiliar specimens by comparing sequentialacquisitions of Auger spectra during continuous electron irra-diation. However, if the change occurs within the acquisitiontime it will not b
37、e seen.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 accelerating voltage, and increas-ing the tilt angle (to increase electron emission). If the s
38、urfaceis 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 generally reduced by increasing theaccelerating voltage and decreasing the angle of incid
39、ence.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. This can beachieved using a variety of methods including the use of liquidnitrogen coo
40、led 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 groundedconducting foil or a conductive mask over the specimen nearthe analyzed region or a grid
41、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 Electron Beam Effects10.1 The conditions that are used to control electron beameffects sh
42、ould be reported in a manner consistent with PracticeE996. This record should, at a minimum, include the electronbeam conditions, such as accelerating voltage, incident current,current density, time of exposure, and incidence angle. If theelectron beam was rastered over the specimen, state the raste
43、rspeed, 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(1) Pantano, C. G. and Madey, T. E., “Electron Beam Damage in AugerElectron Spectrosco
44、py,” 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., “Beam Effects in AESRevealed by XPS,” Discussions of the Faraday Society, Vol 60, 1975,p
45、p. 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) Baer, D.R., Lea, A.S., Geller, J.D., Hammond, J.S., Kover, L., Powell,C.J., Seah, M.P., Suzuki, M., Watts, J.F., Wolstenholme, J
46、., “Ap-proaches to analyzing insulators with Auger electron spectroscopy:Update and overview,” Journal of Electron Spectroscopy and RelatedPhenomena, Vol 176, 2010, pp. 8094.(6) Cazaux, J., “Secondary electron emission and charging mechanisms inAuger Electron Spectroscopy and related e-beam techniqu
47、es,” Jour-nal of Electron Spectroscopy and Related Phenomena, Vol 176, 2010,pp. 5879.(7) Briggs, D., and Grant, J., Surface Analysis by Auger and X-rayPhotoelectron Spectroscopy, IM Publications, West Sussex, UK,Chapters 8 and 9.(8) Field, F. H., and Franklin, J. L., Electron Impact Phenomena Rev. E
48、d.,Academic Press, New York, 1970; Mosiewiksch, B. L., and Smith, S.J., “Electron Impact Excitation at Atoms,” Review of ModernPhysics, Vol 40 (1968) p. 1.(9) Menzel, D. “Desorption Methods,” in Topics in Applied Physics,R.Gomer, Ed., Vol 4, Springer-Verlag, Berlin, 1975, p. 101.(10) Lehman, C., Int
49、eraction of Radiation with Solids and ElementaryDefect Production, North-Holland, Amsterdam, 1977.(11) Musket, R. G. and Ferrante, J., “Auger Electron Spectroscopy Studyof Electron Impact Desorption,” Surface Science, Vol 21, 1970, pp.440442.(12) Coad, J. P., Bishop, H. E., and Rivire, J. C., “Electron-BeamAssisted Adsorption on the Si (111) Surface,” Surface Science,Vol21, 1970, pp. 253264.(13) Thompson, L. F., and Kerwin, R. E., “Polymer Resistivity Systemsfor Photo- and Electron Lithography,” Annual Review of MaterialsScience, Vol 6 (1976) p. 267.(14) Thompson
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