1、Designation: F 1467 99 (Reapproved 2005)Standard Guide forUse of an X-Ray Tester (10 keV Photons) in IonizingRadiation Effects Testing of Semiconductor Devices andMicrocircuits1This standard is issued under the fixed designation F 1467; the number immediately following the designation indicates the
2、year oforiginal adoption or, in the case of revision, the year of last revision. 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 guide covers recommended procedures for the us
3、eof X-ray testers (that is, sources with a photon spectrum having10 keV mean photon energy and 50 keV maximum energy)in testing semiconductor discrete devices and integrated cir-cuits for effects from ionizing radiation.1.2 The X-ray tester may be appropriate for investigatingthe susceptibility of w
4、afer level or delidded microelectronicdevices to ionizing radiation effects. It is not appropriate forinvestigating other radiation-induced effects such as single-event effects (SEE) or effects due to displacement damage.1.3 This guide focuses on radiation effects in metal oxidesilicon (MOS) circuit
5、 elements, either designed (as in MOStransistors) or parasitic (as in parasitic MOS elements inbipolar transistors).1.4 Information is given about appropriate comparison ofionizing radiation hardness results obtained with an X-raytester to those results obtained with cobalt-60 gamma irradia-tion. Se
6、veral differences in radiation-induced effects caused bydifferences in the photon energies of the X-ray and cobalt-60gamma sources are evaluated. Quantitative estimates of themagnitude of these differences in effects, and other factors thatshould be considered in setting up test protocols, are prese
7、nted.1.5 If a 10-keV X-ray tester is to be used for qualificationtesting or lot acceptance testing, it is recommended that suchtests be supported by cross checking with cobalt-60 gammairradiations.1.6 Comparisons of ionizing radiation hardness results ob-tained with an X-ray tester with results obta
8、ined with a linac,with protons, etc. are outside the scope of this guide.1.7 Current understanding of the differences between thephysical effects caused by X-ray and cobalt-60 gamma irradia-tions is used to provide an estimate of the ratio (number-of-holes-cobalt-60)/(number-of-holes-X-ray). Several
9、 cases aredefined where the differences in the effects caused by X raysand cobalt-60 gammas are expected to be small. Other caseswhere the differences could potentially be as great as a factorof four are described.1.8 It should be recognized that neither X-ray testers norcobalt-60 gamma sources will
10、 provide, in general, an accuratesimulation of a specified system radiation environment. Theuse of either test source will require extrapolation to the effectsto be expected from the specified radiation environment. In thisguide, we discuss the differences between X-ray tester andcobalt-60 gamma eff
11、ects. This discussion should be useful asbackground to the problem of extrapolation to effects expectedfrom a different radiation environment. However, the processof extrapolation to the expected real environment is treatedelsewhere (1, 2).21.9 The time scale of an X-ray irradiation and measurementm
12、ay be much different than the irradiation time in the expecteddevice application. Information on time-dependent effects isgiven.1.10 Possible lateral spreading of the collimated X-raybeam beyond the desired irradiated region on a wafer is alsodiscussed.1.11 Information is given about recommended exp
13、erimentalmethodology, dosimetry, and data interpretation.1.12 Radiation testing of semiconductor devices may pro-duce severe degradation of the electrical parameters of irradi-ated devices and should therefore be considered a destructivetest.1.13 The values stated in International System of Units (S
14、I)are to be regarded as standard. No other units of measurementare included in this standard.1This guide is under the jurisdiction of ASTM Committee F01 on Electronicsand is the direct responsibility of Subcommittee F01.11 on Quality and HardnessAssurance.Current edition approved Jan. 1, 2005. Publi
15、shed January 2005. Originallyapproved in 1993. Last previous edition approved in 1999 as F 146799.2The boldface numbers 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 S
16、tates.1.14 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. Refer
17、enced Documents2.1 ASTM Standards:3E 170 Terminology Relating to Radiation Measurementsand DosimetryE 666 Practice for CalculatingAbsorbed Dose from Gammaor X-RadiationE 668 Practice for the Application of Thermoluminescence-Dosimetry (TLD) Systems for DeterminingAbsorbed Dosein Radiation-Hardness T
18、esting of Electronic DevicesE 1249 Practice for Minimizing Dosimetry Errors in Radia-tion Hardness Testing of Silicon Electronic Devices UsingCobalt-60 SourcesE 1894 Guide for Selecting Dosimetry Systems for Appli-cation in Pulsed X-Ray Sources2.2 International Commission on Radiation Quantities and
19、Units Reports:ICRU Report 33Radiation Quantities and Units42.3 United States Department of Defense Standards:MIL-STD-883, Method 1019, Ionizing Radiation (TotalDose) Test Method53. Terminology3.1 Definitions:3.1.1 absorbed-dose enhancement, nincrease (or de-crease) in the absorbed dose (as compared
20、with the equilibriumabsorbed dose) at a point in a material of interest; this can beexpected to occur near an interface with a material of higher orlower atomic number.3.1.2 average absorbed dose, nmass weighted mean ofthe absorbed dose over a region of interest.3.1.3 average absorbed-dose enhanceme
21、nt factor, nratioof the average absorbed dose in a region of interest to theequilibrium absorbed dose.NOTE 1For a description of the necessary conditions for measuringequilibrium absorbed dose see the term “charged particle equilibrium” inTerminology E 170 which provides definitions and descriptions
22、 of otherapplicable terms of this guide. In addition, definitions appropriate to thesubject of this guide may be found in ICRU Report 33.NOTE 2The SI unit for absorbed dose is the gray (Gy), defined as oneJ/kg. The commonly used unit, the rad, is defined in terms of the SI unitsby 1 rad = 0.01 Gy. (
23、For additional information on calculation of absorbeddose see Practice E 666.)3.1.4 equilibrium absorbed dose, nabsorbed dose at someincremental volume within the material in which the conditionof electron equilibrium (the energies, number, and direction ofcharged particles induced by the radiation
24、are constantthroughout the volume) exists (see Terminology E 170).3.1.4.1 DiscussionFor practical purposes the equilibriumabsorbed dose is the absorbed dose value that exists in amaterial at a distance in excess of a minimum distance fromany interface with another material. This minimum distancebein
25、g greater than the range of the maximum energy secondaryelectrons generated by the incident photons.3.1.5 ionizing radiation effects, nthe changes in the elec-trical parameters of a microelectronic device resulting fromradiation-induced trapped charge. These are also sometimesreferred to as “total d
26、ose effects.”3.1.6 time dependent effects, nthe change in electricalparameters caused by the formation and annealing of radiation-induced electrical charge during and after irradiation.4. Significance and Use4.1 Electronic circuits used in many space, military andnuclear power systems may be exposed
27、 to various levels ofionizing radiation dose. It is essential for the design andfabrication of such circuits that test methods be available thatcan determine the vulnerability or hardness (measure ofnonvulnerability) of components to be used in such systems.4.2 Manufacturers are currently selling se
28、miconductor partswith guaranteed hardness ratings, and the military specificationsystem is being expanded to cover hardness specification forparts. Therefore test methods and guides are required tostandardize qualification testing.4.3 Use of low energy (10 keV) X-ray sources has beenexamined as an a
29、lternative to cobalt-60 for the ionizingradiation effects testing of microelectronic devices (3, 4, 5, 6).The goal of this guide is to provide background informationand guidance for such use where appropriate.NOTE 3Cobalt-60The most commonly used source of ionizingradiation for ionizing radiation (“
30、total dose”) testing is cobalt-60. Gammarays with energies of 1.17 and 1.33 MeV are the primary ionizing radiationemitted by cobalt-60. In exposures using cobalt-60 sources, test specimensmust be enclosed in a lead-aluminum container to minimize dose-enhancement effects caused by low-energy scattere
31、d radiation (unless ithas been demonstrated that these effects are negligible). For this lead-aluminum container, a minimum of 1.5 mm of lead surrounding an innershield of 0.7 to 1.0 mm of aluminum is required. (See 8.2.2.2 and PracticeE 1249.)4.4 The X-ray tester has proven to be a useful ionizingr
32、adiation effects testing tool because:4.4.1 It offers a relatively high dose rate, in comparison tomost cobalt-60 sources, thus offering reduced testing time.4.4.2 The radiation is of sufficiently low energy that it canbe readily collimated. As a result, it is possible to irradiate asingle device on
33、 a wafer.4.4.3 Radiation safety issues are more easily managed withan X-ray irradiator than with a cobalt-60 source. This is dueboth to the relatively low energy of the photons and due to thefact that the X-ray source can easily be turned off.4.4.4 X-ray facilities are frequently less costly than co
34、mpa-rable cobalt-60 facilities.4.5 The principal radiation-induced effects discussed in thisguide (energy deposition, absorbed-dose enhancement,electron-hole recombination) (see Appendix X1) will remain3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
35、ice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from International Commission on Radiation Units and Measure-ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814.5Available from Standardizatio
36、n Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094.F 1467 99 (2005)2approximately the same when process changes are made toimprove the performance of ionizing radiation hardness of apart that is being produced. This is the case as long as thethicknesses and compo
37、sitions of the device layers are substan-tially unchanged. As a result of this insensitivity to processvariables, a 10-keV X-ray tester is expected to be an excellentapparatus for process improvement and control.4.6 Several published reports have indicated success inintercomparing X-ray and cobalt-6
38、0 gamma irradiations usingcorrections for dose enhancement and for electron-hole recom-bination. Other reports have indicated that the present under-standing of the physical effects is not adequate to explainexperimental results. As a result, it is not fully certain that thedifferences between the e
39、ffects of X-ray and cobalt-60 gammairradiation are adequately understood at this time. (See 8.2.1and Appendix X2.) Because of this possible failure of under-standing of the photon energy dependence of radiation effects,if a 10-keV X-ray tester is to be used for qualification testingor lot acceptance
40、 testing, it is recommended that such testsshould be supported by cross checking with cobalt-60 gammairradiations. For additional information on such comparison,see X2.2.4.4.7 Because of the limited penetration of 10-keV photons,ionizing radiation effects testing must normally be performedon unpacka
41、ged devices (for example, at wafer level) or onunlidded devices.5. Interferences5.1 Absorbed-Dose EnhancementAbsorbed-dose en-hancement effects (see 8.2.1 and X1.3) can significantlycomplicate the determination of the absorbed dose in the regionof interest within the device under test. In the photon
42、 energyrange of the X-ray tester, these effects should be expected whenthere are regions of quite different atomic number withinhundreds of nanometers of the region of interest in the deviceunder test.NOTE 4An example of a case where significant absorbed doseenhancement effects should be expected is
43、 a device with a tantalumsilicide metallization within 200 nm of the SiO2gate oxide.5.2 Electron-Hole RecombinationOnce the absorbed dosein the sensitive region of the device under test is determined,interpretation of the effects of this dose can be complicated byelectron-hole recombination (see 8.2
44、.1 and X1.5).5.3 Time-Dependent EffectsThe charge in device oxidesand at silicon-oxide interfaces produced by irradiation maychange with time. Such changes take place both during andafter irradiation. Because of this, the results of electricalmeasurements corresponding to a given absorbed dose can b
45、ehighly dependent upon the dose rate and upon the time duringand after the irradiation at which the measurement takes place(see X1.7 for further detail).NOTE 5The dose rates used for X-ray testing are frequently muchhigher than those used for cobalt-60 testing. For example, cobalt-60testing is speci
46、fied by Military Test Method 1019.4 to be in the range of0.5 to 3 Gy(Si)/s (50 to 300 rads/(Si)/s). For comparison, X-ray testing iscommonly carried out in the range of 2 to 30 Gy(Si)/s (200 to 3000rads(Si)/s).5.4 HandlingAs in any other type of testing, care must betaken in handling the parts. This
47、 especially applies to parts thatare susceptible to electrostatic discharge damage.6. Apparatus6.1 X-Ray Tester A suitable X-ray tester (see Ref (3)consists of the following components:6.1.1 Power Supply The power supply typically supplies10 to 100 mA at 25 to 60 keV (constant potential) to the X-ra
48、ytube.6.1.2 X-Ray TubeIn a typical commercial X-ray tube apartially focused beam of electrons strikes a water-cooledmetal target. The target material most commonly used forionizing radiation effects testing is tungsten, though some workhas been done using a copper target. X-ray tubes are limited byt
49、he power they can dissipate. A maximum power of 3.5 kW istypical.6.1.3 CollimatorA collimator is used to limit the regionon a wafer which is irradiated. A typical collimator is con-structed of 0.0025 cm of tantalum.6.1.4 FilterA filter is used to remove the low-energyphotons produced by the X-ray tube. A typical filter is 0.0127cm (0.005 in.) of aluminum.6.1.5 DosimeterA dosimetric system is required to mea-sure the dose delivered by the X-ray tube (see Guide E 1894).NOTE 6X-ray testers typically use a calibrated diode to measure thedose delivered by the
