1、Designation: E1249 10Standard 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 Department of Defense.1. Scope1.1
3、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 silicon
4、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 may b
5、e 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 electroni
6、c 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 spectrum is
7、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-60sources,
8、 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 provides
9、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 absorbed-
10、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 does
11、 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 Stand
12、ards:2E170 Terminology Relating to Radiation Measurements andDosimetry2E666 Practice for CalculatingAbsorbed Dose From Gammaor X Radiation2E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for DeterminingAbsorbed Dosein Radiation-Hardness Testing of Electronic Devices2E1250
13、 Test Method forApplication of Ionization Chambersto Assess the Low Energy Gamma Component ofCobalt-60 Irradiators Used in Radiation-Hardness Testingof Silicon Electronic Devices2.2 International Commission on Radiation Units andMeasurements Reports:ICRU Report 14 Radiation Dosimetry: X-Rays and Gam
14、maRays With Maximum Photon Energies Between 0.6 and50 MeV3ICRU Report 18 Specification of High Activity Gamma-Ray Sources31This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry
15、 for Radiation Effects on Materials and Devices.Current edition approved Dec. 1, 2010. Published January 2011. Originallyapproved in 1988. Last previous edition approved in 2005 as E124900(2005). DOI:10.1520/E1249-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AST
16、M Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Commission on Radiation Units, 7910 WoodmontAve., Washington, DC 20014.1Copyright ASTM International, 100 Barr Har
17、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1 absorbermaterial 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 abso
18、rbeddose) at a point in a material of interest. This can be expectedto occur near an interface with a material 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
19、.4 average absorbed dosemass weighted mean of theabsorbed dose over a region of interest.3.5 average absorbed-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 measuringequilib
20、rium absorbed dose, see 6.3.1 and the term charged particleequilibrium in Terminology E170, which provides 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 pur
21、pose is to eliminate the scattering of the transmittedbeam back into the device under test.3.7 clean spectrumone that is relatively free of lowenergy components in the photon energy spectrum. For ex-ample, for a Co-60 source an ideally clean spectrum wouldcontain only the primary 1.17 and 1.33 MeV p
22、hotons of Co-60decay.3.8 equilibrium absorbed doseabsorbed dose at someincremental volume within the material in which the conditionof charged particle equilibrium (the energies, number, anddirection of charged particles induced by the radiation areconstant throughout the volume) exists (see Termino
23、logyE170).NOTE 4For practical purposes the equilibrium absorbed dose is theabsorbed dose value that exists 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, m
24、ade of one or more layers ofdifferent materials, surrounding a device under test or adosimeter, or both, for 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 dev
25、ice under test.The purpose of the filter is to reduce low energy components ofthe photon energy spectrum.3.11 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 o
26、f the photon energy spectrum isincreased.4. Significance and Use4.1 Division of the Co-60 Hardness Testing 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 t
27、heposition of the device before or after irradiation of the device.4.1.2 This absorbed dose measured by the 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.
28、4.1.3 A correction for absorbed-dose enhancement effectsshall be considered. This correction is dependent upon 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 so
29、me electrically important effect(such as charge trapped at the Si/SiO2interface as manifestedby a shift in 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 5
30、The 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 covered 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 Component
31、s in the SpectrumSome of theprimary Co-60 gamma rays (1.17 and 1.33 MeV) producelower energy photons by Compton 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 backsca
32、ttering. As a result of thecomplexity of these effects, the photon energy spectrumstriking the device usually 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 define
33、s test procedures thatshould minimize dosimetry errors without the need to know thespectrum. These recommended 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 materia
34、l of the dosimeter (such as the CaF2of aTLD) to theequivalent absorbed dose in the material of interest (such as theSiO2of the gate oxide of a device) is dependent on the incidentphoton energy spectrum. However, if the simplifying assump-tion is made that all incident photons have the energies of th
35、eprimary 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 dosimeter and device materials. Where thissimplification is appropriate, the error incurred by its use
36、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 deposition in the region adjacent to theinterface is a complex function of the incident photon en
37、ergy4The boldface numbers in parentheses refer to the list of references appended tothis practice.E1249 102spectrum, 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 outlin
38、ed in 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 of nanome-tres, absorbed-dose enhancement effects are a characteristicp
39、roblem for irradiation of such devices (see 6.1 and AppendixX2).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 en
40、ergy components 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 k
41、nowledge 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. How-ever, if the
42、 methods specified in Section 7 are used to minimizeabsorbed-dose enhancement effects, errors due to the absenceof a correction for these effects can be kept within bounds thatmay be acceptable for many users. An estimate of these errorbounds for representative cases is given in Section 7 andAppendi
43、x X5.4.7 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. De
44、scription 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 on struc-tures, usually of aluminum alloys or stainless steel. For somesources, the output is collimated
45、 using iron, lead, or otherhigh-density metals or combinations of these absorbers. Fi-nally, 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
46、 low energy 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 Re
47、f (2) and Appendix 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.
48、NOTE 7A qualitative 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 ty
49、pical sources, a nominal photon energy spec-trum 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 materia
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