1、Designation: E1249 15Standard Practice forMinimizing Dosimetry Errors in Radiation Hardness Testingof Silicon Electronic Devices Using Co-60 Sources1This standard is issued under the fixed designation E1249; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scop
3、e1.1 This practice covers recommended procedures for theuse of dosimeters, such as thermoluminescent dosimeters(TLDs), to determine the absorbed dose in a region of interestwithin an electronic device irradiated using a Co-60 source.Co-60 sources are commonly used for the absorbed dosetesting of sil
4、icon electronic devices.NOTE 1This absorbed-dose testing is sometimes called “total dosetesting” to distinguish it from “dose rate testing.”NOTE 2The effects of ionizing radiation on some types of electronicdevices may depend on both the absorbed dose and the absorbed dose rate;that is, the effects
5、may be different if the device is irradiated to the sameabsorbed-dose level at different absorbed-dose rates. Absorbed-dose rateeffects are not covered in this practice but should be considered inradiation hardness testing.1.2 The principal potential error for the measurement ofabsorbed dose in elec
6、tronic devices arises from non-equilibrium energy deposition effects in the vicinity of materialinterfaces.1.3 Information is given about absorbed-dose enhancementeffects in the vicinity of material interfaces. The sensitivity ofsuch effects to low energy components in the Co-60 photonenergy spectru
7、m is emphasized.1.4 A brief description is given of typical Co-60 sourceswith special emphasis on the presence of low energy compo-nents in the photon energy spectrum output from such sources.1.5 Procedures are given for minimizing the low energycomponents of the photon energy spectrum from Co-60sou
8、rces, using filtration. The use of a filter box to achieve suchfiltration is recommended.1.6 Information is given on absorbed-dose enhancementeffects that are dependent on the device orientation with respectto the Co-60 source.1.7 The use of spectrum filtration and appropriate deviceorientation prov
9、ides a radiation environment whereby theabsorbed dose in the sensitive region of an electronic devicecan be calculated within defined error limits without detailedknowledge of either the device structure or of the photonenergy spectrum of the source, and hence, without knowing thedetails of the abso
10、rbed-dose enhancement effects.1.8 The recommendations of this practice are primarilyapplicable to piece-part testing of electronic devices. Elec-tronic circuit board and electronic system testing may intro-duce problems that are not adequately treated by the methodsrecommended here.1.9 This standard
11、 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-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM
12、Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE666 Practice for Calculating Absorbed Dose From Gammaor X RadiationE668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining AbsorbedDose in Radiation-Hardness Testing of Electronic DevicesE
13、1250 Test Method for Application of Ionization Chambersto Assess the Low Energy Gamma Component of1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applicationsand is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on
14、 Materials and Devices.Current edition approved June 1, 2015. Published July 2015. Originally approvedin 1988. Last previous edition approved in 2010 as E124910. DOI: 10.1520/E1249-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm
15、.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Cobalt-60 Irradiators Used in Radiation-Hardness Testingof Sili
16、con Electronic Devices2.2 International Commission on Radiation Units and Mea-surements Reports:ICRU Report 14 Radiation Dosimetry: X-Rays and GammaRays With Maximum Photon Energies Between 0.6 and50 MeV3ICRU Report 18 Specification of HighActivity Gamma-RaySources33. Terminology3.1 absorbermaterial
17、 that reduces the photon fluence ratefrom a Co-60 source by any interaction mechanism.3.2 absorbed-dose enhancementincrease (or decrease) inthe absorbed dose (as compared to the equilibrium absorbeddose) at a point in a material of interest. This can be expectedto occur near an interface with a mate
18、rial of higher or loweratomic number.3.3 absorbed-dose enhancement factor ratio of the ab-sorbed dose at a point in a material of interest to theequilibrium absorbed dose in that same material.3.4 average absorbed dosemass weighted mean of theabsorbed dose over a region of interest.3.5 average absor
19、bed-dose enhancement factorratio ofthe average absorbed dose in a region of interest to theequilibrium absorbed dose (1).4NOTE 3For a description of the necessary conditions for measuringequilibrium absorbed dose, see 6.3.1 and the term charged particleequilibrium in Terminology E170, which provides
20、 definitions and descrip-tions of other applicable terms of this practice.3.6 beam trapabsorber that is designed to remove thebeam that has been transmitted through the device under test.Its purpose is to eliminate the scattering of the transmittedbeam back into the device under test.3.7 clean spect
21、rumone that is relatively free of low energycomponents in the photon energy spectrum. For example, for aCo-60 source an ideally clean spectrum would contain only theprimary 1.17 and 1.33 MeV photons of Co-60 decay.3.8 equilibrium absorbed doseabsorbed dose at someincremental volume within the materi
22、al in which the conditionof charged particle equilibrium (the energies, number, anddirection of charged particles induced by the radiation areconstant throughout the volume) exists (see TerminologyE170).NOTE 4For practical purposes the equilibrium absorbed dose is theabsorbed dose value that exists
23、in a material at a distance from anyinterface with another material, greater than the range of the maximumenergy secondary electrons generated by the incident photons.3.9 filter boxcontainer, made of one or more layers ofdifferent materials, surrounding a device under test or adosimeter, or both, fo
24、r the purpose of minimizing low energycomponents of the incident photon energy spectrum.3.10 spectrum filtermaterial layer intercepting photons ontheir path between the Co-60 source and the device under test.The purpose of the filter is to reduce low energy components ofthe photon energy spectrum.3.
25、11 spectrum hardeningprocess by which the fraction oflow energy components of the photon energy spectrum isreduced.3.12 spectrum softeningprocess by which the fraction oflow energy components of the photon energy spectrum isincreased.4. Significance and Use4.1 Division of the Co-60 Hardness Testing
26、into Five Parts:4.1.1 The equilibrium absorbed dose shall be measured witha dosimeter, such as a TLD, located adjacent to the deviceunder test. Alternatively, a dosimeter may be irradiated in theposition of the device before or after irradiation of the device.4.1.2 This absorbed dose measured by the
27、 dosimeter shallbe converted to the equilibrium absorbed dose in the materialof interest within the critical region within the device undertest, for example the SiO2gate oxide of an MOS device.4.1.3 A correction for absorbed-dose enhancement effectsshall be considered. This correction is dependent u
28、pon thephoton energy that strikes the device under test.4.1.4 A correlation should be made between the absorbeddose in the critical region (for example, the gate oxidementioned in 4.1.2) and some electrically important effect(such as charge trapped at the Si/SiO2interface as manifestedby a shift in
29、threshold voltage).4.1.5 An extrapolation should then be made from the resultsof the test to the results that would be expected for the deviceunder test under actual operating conditions.NOTE 5The parts of a test discussed in 4.1.2 and 4.1.3 are the subjectof this practice. The subject of 4.1.1 is c
30、overed and referenced in otherstandards such as Practice E668 and ICRU Report 14. The parts of a testdiscussed in 4.1.4 and 4.1.5 are outside the scope of this practice.4.2 Low-Energy Components in the SpectrumSome of theprimary Co-60 gamma rays (1.17 and 1.33 MeV) producelower energy photons by Com
31、pton scattering within the Co-60source structure, within materials that lie between the sourceand the device under test, and within materials that lie beyondthe device but contribute to backscattering. As a result of thecomplexity of these effects, the photon energy spectrumstriking the device usual
32、ly is not well known. This point isfurther discussed in Section 5 and Appendix X1. The presenceof low-energy photons in the incident spectrum can result indosimetry errors. This practice defines test procedures thatshould minimize dosimetry errors without the need to know thespectrum. These recommen
33、ded procedures are discussed in4.5, 4.6, Section 7, and Appendix X5.4.3 Conversion to Equilibrium Absorbed Dose in the DeviceMaterialThe conversion from the measured absorbed dose inthe material of the dosimeter (such as the CaF2of aTLD) to theequivalent absorbed dose in the material of interest (su
34、ch as theSiO2of the gate oxide of a device) is dependent on the incident3Available from International Commission on Radiation Units, 7910 WoodmontAve., Washington, DC 20014.4The boldface numbers in parentheses refer to the list of references appended tothis practice.E1249 152photon energy spectrum.
35、However, if the simplifying assump-tion is made that all incident photons have the energies of theprimary Co-60 gamma rays, then the conversion from absorbeddose in the dosimeter to that in the device under test can bemade using tabulated values for the energy absorption coeffi-cients for the dosime
36、ter and device materials. Where thissimplification is appropriate, the error incurred by its use todetermine equilibrium absorbed dose is usually less than 5 %(see 6.3).4.4 Absorbed-Dose Enhancement Effects If a higheratomic number material lies adjacent to a lower atomic numbermaterial, the energy
37、deposition in the region adjacent to theinterface is a complex function of the incident photon energyspectrum, the material composition, and the spatial arrange-ment of the source and absorbers. The absorbed dose near suchan interface cannot be adequately determined using the proce-dure outlined in
38、4.3. Errors incurred by failure to account forthese effects may, in unusual cases, exceed a factor of five.Because microelectronic devices characteristically contain lay-ers of dissimilar materials with thicknesses of tens ofnanometres, absorbed-dose enhancement effects are a charac-teristic problem
39、 for irradiation of such devices (see 6.1 andAppendix X2).4.5 Minimizing Absorbed-Dose Enhancement EffectsUnder some circumstances, absorbed-dose enhancement ef-fects can be minimized by hardening the spectrum. Hardeningis accomplished by the use of high atomic number absorbers toremove low energy c
40、omponents of the spectrum, and byminimizing the amount and proximity of low atomic numbermaterial to reduce softening of the spectrum by Comptonscattering (see Sections 6 and 7).4.6 Limits of the Dosimetry Errors To correct forabsorbed-dose enhancement by calculational methods wouldrequire a knowled
41、ge of the incident photon energy spectrumand the detailed structure of the device under test. To measureabsorbed-dose enhancement would require methods for simu-lating the irradiation conditions and device geometry. Suchcorrections are impractical for routine hardness testing.However, if the methods
42、 specified in Section 7 are used tominimize absorbed-dose enhancement effects, errors due to theabsence of a correction for these effects can be kept withinbounds that may be acceptable for many users. An estimate ofthese error bounds for representative cases is given in Section7 and Appendix X5.4.7
43、 Application to Non-Silicon Devices The material ofthis practice is primarily directed toward silicon based solidstate electronic devices. The application of the material andrecommendations presented here should be applied to galliumarsenide and other types of devices only with caution.5. Descriptio
44、n of Co-60 Sources5.1 Cobalt-60 principally decays by emitting gamma rays of1.17 and 1.33 MeV. In most sources, Co-60 is doubly encap-sulated in stainless steel; the sources are supported onstructures, usually of aluminum alloys or stainless steel. Forsome sources, the output is collimated using iro
45、n, lead, or otherhigh-density metals or combinations of these absorbers.Finally, shielding materials of tungsten, lead, concrete, or waterare often present. Therefore, a significant fraction of thephotons incident on the device under test are the result ofCompton scattering that produces low energy
46、components inthe source output photon energy spectrum (see ICRU Report18 for additional discussion of gamma-ray sources).NOTE 6As an example, the energy spectrum from even a relativelyclean Co-60 source has about 35 % of its total number of photons withenergies of less than 1 MeV (see Ref (2) and Ap
47、pendix X1).5.2 Even for a given source, a considerable variability existsin the output energy spectrum depending on the geometry andposition of irradiation. The spectrum at any position is affectedby scattering from walls, floor, and ceiling and by scatteringfrom material located nearby.NOTE 7A qual
48、itative estimate of the spectrum hardness for a givensource can be obtained using Method E1250.5.3 The following Co-60 source types are described brieflyand listed in the order of decreasing relative spectrum hardnessunder the most favorable conditions of irradiation.NOTE 8Diagrams of typical source
49、s, a nominal photon energyspectrum for each, and references are given in Appendix X1.5.3.1 A teletherapy source is a completely shielded sourcefrom which the photon output is confined to a beam that isusually collimated. The source output is typically directed intoa shielded room, but a shielded container, or box, is used insome cases.5.3.2 A room source is a source contained in a shielded wellfrom which it is moved into a shielded room by remote control.Its position in the room relative to walls, floor, and ceiling andother scattering material determines t
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