1、Designation: E 1127 03Standard Guide forDepth Profiling in Auger Electron Spectroscopy1This standard is issued under the fixed designation E 1127; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、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 guide covers procedures used for depth profiling inAuger electron spectroscopy.1.2 Guidelines are given for depth profiling by the follo
3、w-ing:SectionIon Sputtering 6Angle Lapping and Cross-Sectioning 7Mechanical Cratering 8Nondestructive Depth Profiling 91.3 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-pri
4、ate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 673 Terminology Relating to Surface Analysis2E 684 Practice for Approximate Determination of CurrentDensity of Large-Diameter Ion Beams for Sputter Dept
5、hProfiling of Solid Surfaces2E 827 Practice for Elemental Identification by Auger Elec-tron Spectroscopy2E 1634 Guide for Performing Sputter Crater Depth Mea-surements23. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this guide, refer toTerminology E 673.4. Summary of Guide4.1 In
6、 ion sputtering, the surface layers are removed by ionbombardment in conjunction with Auger analysis.4.2 In angle lapping, the surface is lapped or polished at asmall angle to improve the depth resolution as compared to across section.4.3 In mechanical cratering, a spherical or cylindrical crateris
7、created in the surface using a rotating ball or wheel. Thesloping sides of the crater are used to improve the depthresolution as in angle lapping.4.4 In nondestructive techniques, different methods of vary-ing the electron information depth are involved.5. Significance and Use5.1 Auger electron spec
8、troscopy yields information con-cerning the chemical and physical state of a solid surface in thenear surface region. Nondestructive depth profiling is limitedto this near surface region. Techniques for measuring the craterdepths and film thicknesses are given in (35).5.2 Ion sputtering is primarily
9、 used for depths of less thanthe order of 1 m.5.3 Angle lapping or mechanical cratering is primarily usedfor depths greater than the order of 1 m.5.4 The choice of depth profiling methods for investigatingan interface depends on surface roughness, interface rough-ness, and film thickness (1).36. Ion
10、 Sputtering6.1 First introduce the specimen into a vacuum chamberequipped with an Auger analyzer and an ion sputtering gun.Align the ion beam using a sputtering target or a Faraday cup,paying careful attention to the relative spot size of the electronbeam, ion beam, and Faraday cup and their respect
11、ive orien-tations to ensure accurate convergence of the two beams at thespecimen surface.6.1.1 Place the specimen in front of the Auger analyzer anddirect the ion gun towards the analysis area. If the ion beam isnot normal to the specimen surface then possible shadowing ofthe analysis area from the
12、ion beam must be considered.6.2 Choose the elements to be investigated from previousexperience or from an initial Auger electron spectrum or anenergy-dispersive X-ray spectrum since the latter spectrum canreveal additional elements present at depths greater than thosethat contribute to the Auger ele
13、ctron spectrum (2). Select aspecific transition for each element. During the depth profiling,record the peak-to-peak heights for Auger derivative data, orpeak heights or peak areas for N(E) data. The data may be1This guide is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the
14、 direct responsibility of Subcommittee E42.03 on Auger ElectronSpectroscopy and XPS.Current edition approved May 10, 2003. Published September 2003. Originallyapproved in 1986. Last previous edition approved in 1997 as E 1127 91 (1997).2Annual Book of ASTM Standards, Vol 03.06.3The boldface numbers
15、in parentheses refer to the list of references at the end ofthis guide.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.gathered during continuous sputtering or between timed sputtersegments. Results may vary between the two technique
16、s.6.2.1 One source of their difference is due to the presence ofion-induced electrons during continuous sputter depth profil-ing, especially at low-electron kinetic energies, that can be-come comparable in intensity to the electrons induced by theprobing incident electron beam. Unless one or the oth
17、er of theexcitation beams is modulated and detected synchronouslythese two types of emitted electrons are difficult to distinguish.These ion-induced electrons usually form a featureless back-ground that rises steeply as their kinetic energy decreases, butsometimes ion-induced Auger peaks might be pr
18、esent whoselineshape may be different from those produced by the electronbeam (3). As a result, care must be taken during continuoussputtering to ensure reliable results. Another source of differ-ence is due to the buildup of adsorbed species during the dataacquisition time in the discontinuous sput
19、ter depth profilemode (4). If portions of the ion-eroded surface expose veryreactive phases, then Auger peaks due to adsorbed species, forexample, oxygen or carbon, or both, will appear in the spectraand mask the actual depth distribution.6.2.2 It is advisable when analyzing an unknown specimento pe
20、riodically examine survey scans to detect any newelements that were not present in the initial survey scan and todetermine if any of the Auger peaks have been displacedoutside of their analysis windows (5).6.3 Crater-edge profiling of the sputter-formed crater byusing Auger line scans is a technique
21、 similar to the analysis ofthe mechanically formed craters in Section 8 (6). Forming thecrater by sputtering may introduce the additional complicationsof ion-induced damage and asymmetric crater dimensions.6.4 If specimen rotation is used to reduce ion-inducedroughness, then the rotational speed, ro
22、tation axis runoutrelative to ion beam sputtered area or wobble and dataacquisition rate should be reported (7 and 8).6.5 Identify the elements in the survey scans using PracticeE 827.6.6 The Auger data and the sputtering conditions should bereported as described in Practice E 996.6.7 There is exten
23、sive information available in the literatureon the effects of ion bombardment on solid surfaces (9-14).6.8 Special care must be exercised whenever specimentemperature changes are present because effects due to surfacediffusion, surface segregation or diffusion limited bulk pro-cesses such as point d
24、efect migration can occur and dramati-cally alter the specimen composition, even over depths largerthan the ion beam penetration depth which is typically a fewnanometers (15 and 16). The concept of preferential sputteringin multielement, single-phase specimens has altered signifi-cantly so that chem
25、ical effects such as surface segregation areconsidered to be at least as important as physical effects suchas mass differences in the evolution of the near surfacecomposition during sputter depth profiling (17-20). Since theprobing depths in Auger electron spectroscopy are usuallysmaller than the io
26、n-penetration depth these effects are veryimportant in any interpretation of Auger signal intensity interms of composition during ion-beam profiling. Computermodelling of these and other ion-induced phenomena has beenextensively studied and has provided new insights into thisfield (21 and 22).6.8.1
27、It should be determined for each specimen if compo-sitional changes or other sputter effects are likely to occur. Itmay be possible to minimize these effects in some instances byadjusting the sputtering parameters.6.9 Ion guns used in Auger analysis are normally self-contained units capable of produ
28、cing a focused beam of ions.The specimen is not used as an anode for the gun. Many ionguns are able to raster the ion beam. A rastered ion beam willproduce a more uniform ion current distribution on thespecimen surface in the region of analysis.6.10 If the ion gun is differentially pumped, the vacuu
29、mpumps may be left on during sputtering, removing most of thesputtered gases. If not, then the chamber must be back filledwith gas and provisions for removing the sputtered active gasesmust be considered. Titanium sublimation is effective inremoving these gases.6.11 Noble gas ions are normally used
30、in sputtering and themost commonly used gas is argon. Xenon is occasionally usedwith high beam energies when rapid sputtering is needed.Active gases such as oxygen and metal ions are used in specialcircumstances.6.11.1 Ion energies commonly used for depth profilingusing noble gases are in the range
31、from 1 to 5 keV where lowerion energies are usually preferred for improved depth resolu-tion. Higher ion energies usually can be obtained with higherion currents and less preferential sputtering.6.11.2 Ion beam current density can be measured by aFaraday cup or by following Practice E 684.6.11.3 The
32、 sputter rate is needed to calibrate the depth scale(33, 34, Guide E 1634) when depth profiling using ionsputtering. Several reference standards are available for thispurpose. One reference material consists of 30 and 100-nmthick tantalum pentoxide films (23).4Another reference mate-rial is an alter
33、nating nickel and chromium thin film structure;each layer is nominally 50-nm thick.57. Angle Lapping and Cross-Sectioning7.1 In cross-sectioning, polish the specimen perpendicularto the interface, while in angle lapping, polish the specimen atan angle to increase the depth resolution as shown in Fig
34、. 1(24). Polishing usually includes the use of silicon carbidepapers, diamond paste, and alumina. Use progressively finerpolishing particles to obtain the desired surface finish. Possiblelimitations of the techniques include smearing of materialacross the interface, surface roughness, and the electr
35、on probediameter limiting the spatial resolution.7.2 In angle lapping mount the specimen on a flat gageblock and measure the angle with a collimator. The accuracydepends on the flatness of the specimen. In practice an angle of0.1 can be accurately measured.4Available from the National Physical Labor
36、atory, Teddington, Middlesex,England. Listed as Certified Reference Material NPL No. S7B83, BCR No. 261.5Available from the National Institute of Standards and Technology, U.S.Department of Commerce, Gaithersburg, MD 20899. Listed as NIST StandardReference Material 2135.E11270327.3 The depth, d, is
37、given by the following equation:d 5 Y tan u (1)where (in Fig. 1) u is the lapped angle and Y is the distancefrom the edge.7.4 The depth resolution, Dd, is given by the followingequation:Dd 5DY tan u (2)where DY includes the electron beam diameter and uncer-tainties in position that may be due to err
38、ors in specimen orelectron beam positioning.7.5 Auger analysis can include line scans and point analysisalong the lapped surface. Perform the analysis by eithermoving the specimen using micrometer adjustments or byelectronically moving the electron beam.7.6 Ion sputtering (Section 6) is often used i
39、n conjunctionwith angle lapping to remove contaminants and to investigateinterfaces beneath the lapped surfaces.7.7 Consideration should be given if specimen mountingmethods, for example, plastic embedding media, are usedwhich may employ high vapor pressure materials. Out-gassingof the media as well
40、 as trapped gases between the media andthe specimen may require complete removal of the mountingmaterials prior to analysis.8. Mechanical Cratering8.1 Ball Cratering:8.1.1 First mount the specimen in a device where a rotatingsteel ball can be placed against its surface. Commercialapparatus is availa
41、ble that uses a rotating shaft with a notch thatholds the ball and spins it. The rotational speed and the forceagainst the specimen can be adjusted (25).8.1.2 Coat the ball with an abrasive material to improve thecratering rate. In practice diamond paste is used with a particlesize of 0.1 to 1 m. Th
42、e larger particle sizes will give the mostrapid cratering rates and the finer particle sizes will give thesmoothest crater wall surface. The coarser pastes can be usedfirst to form the crater and the fine pastes can be used to smooththe crater wall. As with cross-sectioning and angle lapping,conside
43、ration should be given to the possibility of smearingmaterial across the cratered surface.8.1.3 The geometry of the crater is shown in Fig. 2. Thedepth of the crater, d, is given by the following equation:d 5 D2/8R (3)where:D = the diameter of the crater,R = the radius of the ball, andR =D/2.8.1.4 T
44、he Auger analysis is the same as described in 7.5 and7.6.8.1.5 The depth at any point in the analysis, Z, is given bythe following equation (1):Z 5 R22 x21 Dx 2 D2/4!1/22 R22 D2/4!1/2(4)where x is the lateral distance from the crater edge. Thedepth may also be given by the approximation as follows:Z
45、 5 xD 2 x!/2R (5)8.1.6 The depth resolution, DZ, is given by the followingequation:DZ 5Dx tan u (6)where Dx includes the electron beam diameter and otheruncertainties in lateral position and u is the taper angle. Incontrast to angle lapping (Section 7), the taper angle, which isdefined as the angle
46、between the surface and the tangent to thecrater, varies in value along the crater wall. Its value is givenby the following equation:sin u50.5D 2 x!2/R (7)The best resolution is when u is the smallest at the craterbottom.8.2 Radial SectioningA technique similar to ball crateringthat uses a cylindric
47、al grinding tool instead of a spherical one(26).9. Nondestructive Depth Profiling9.1 Methods for nondestructive depth profiling with Augerelectron spectroscopy are based upon varying the effectiveelectron escape depth from the specimen and are limited tocharacterizing the outermost 2 to 5 nm.9.2 For
48、 certain elements, a depth dependence may be foundby examining Auger transitions of different energies (27). Thelower energy Auger electrons will have a shallower escapedepth than the more energetic electrons and therefore, differenttransitions for the same element will have different samplingdepths
49、.NOTE 1In practice, the angle u is much smaller than shown, being ofthe order of 1FIG. 1 Cross Section of Angle-Lapped SpecimenFIG. 2 Cross Section of Specimen After Ball-Cratering Using aSphere of Radius, R, to a depth, dE11270339.3 The sampling depth may also be varied to a limiteddegree by varying the incident electron beam energy toproduce a weak depth dependence in the excitation volume ofthe specimen (28).9.4 Angle-resolved Auger electron spectroscopy, which in-volves varying the collected take-off angle of the emittedelectrons, has been used for depth profiling (29),
