1、Designation: F996 11 (Reapproved 2018)Standard Test Method forSeparating an Ionizing Radiation-Induced MOSFETThreshold Voltage Shift Into Components Due to OxideTrapped Holes and Interface States Using the SubthresholdCurrentVoltage Characteristics1This standard is issued under the fixed designation
2、 F996; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapprova
3、l.1. Scope1.1 This test method covers the use of the subthresholdcharge separation technique for analysis of ionizing radiationdegradation of a gate dielectric in a metal-oxide-semiconductor-field-effect transistor (MOSFET) and an isola-tion dielectric in a parasitic MOSFET.2,3,4The subthresholdtech
4、nique is used to separate the ionizing radiation-inducedinversion voltage shift, VINVinto voltage shifts due to oxidetrapped charge, Votand interface traps, Vit. This techniqueuses the pre- and post-irradiation drain to source current versusgate voltage characteristics in the MOSFET subthresholdregi
5、on.1.2 Procedures are given for measuring the MOSFET sub-threshold current-voltage characteristics and for the calculationof results.1.3 The application of this test method requires the MOS-FET to have a substrate (body) contact.1.4 Both pre- and post-irradiation MOSFET subthresholdsource or drain c
6、urves must follow an exponential dependenceon gate voltage for a minimum of two decades of current.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns, if a
7、ny, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accor-dance with internatio
8、nally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:5E666 Pract
9、ice 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 DevicesE1249 Practice for Minimizing Dosimetry Errors in Radia-tion Hardness Testing of Silic
10、on Electronic Devices UsingCo-60 SourcesE1894 Guide for Selecting Dosimetry Systems for Applica-tion in Pulsed X-Ray Sources3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 anneal conditionsthe current and/or voltage bias andtemperature of the MOSFET in the time period betweeni
11、rradiation and measurement.3.1.2 doping concentration n-orp-type doping, is theconcentration of the dopant in the MOSFET channel regionadjacent to the oxide/silicon interface.1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommit
12、tee F01.11 on Nuclear andSpace Radiation Effects.Current edition approved March 1, 2018. Published April 2018. Originallyapproved in 1991. Last previous edition approved in 2011 as F996 11. DOI:10.1520/F0996-11R18.2McWhorter, P. J. and P. S. Winokur, “Simple Technique for Separating theEffects of In
13、terface Traps and Trapped Oxide Charge in MOS Transistors,” AppliedPhysics Letters, Vol 48, 1986, pp. 133135.3DNA-TR-89-157, Subthreshold Technique for Fixed and Interface TrappedCharge Separation in Irradiated MOSFETs, available from National TechnicalInformation Service, 5285 Port Royal Rd., Sprin
14、gfield, VA 22161.4Saks, N. S., and Anacona, M. G., “Generation of Interface States by IonizingRadiation at 80K Measured by Charge Pumping and Subthreshold SlopeTechniques,” IEEE Transactions on Nuclear Science, Vol NS34 , No. 6, 1987, pp.13481354.5For referenced ASTM standards, visit the ASTM websit
15、e, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesT
16、his international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade
17、(TBT) Committee.13.1.3 Fermi levelthis value describes the top of thecollection of electron energy levels at absolute zero tempera-ture.3.1.4 intrinsic Fermi levelthe energy level that the Fermilevel has in the absence of any doping.3.1.5 inversion current, IINVthe MOSFET channel currentat a gate-so
18、urce voltage equal to the inversion voltage.3.1.6 inversion voltage, VINVthe gate-source voltage cor-responding to a surface potential of 2B.3.1.7 irradiation biasesthe biases on the gate, drain,source, and substrate of the MOSFET during irradiation.3.1.8 midgap current, IMGthe MOSFET channel curren
19、t ata gate-source voltage equal to the midgap voltage.3.1.9 midgap voltage, VMGthe gate-source voltage corre-sponding to a surface potential of B.3.1.10 oxide thickness, toxthe thickness of the oxide of theMOSFET under test.3.1.11 potential, Bthe potential difference between theFermi level and the i
20、ntrinsic Fermi level.3.1.12 subthreshold swingthe change in the gate-sourcevoltage per change in the log source or drain current of theMOSFET channel current below the inversion current. Thevalue of the subthreshold swing is expressed in V/decade (ofcurrent).3.1.13 surface potential, sthe potential
21、at the MOSFETsemiconductor surface measured with respect to the intrinsicFermi level.4. Summary of Test Method4.1 The subthreshold charge separation technique is basedon standard MOSFET subthreshold current-voltage character-istics. The subthreshold drain or source current at a fixed drainto source
22、voltage, VDS, is measured as a function of gatevoltage from the leakage current (or limiting resolution of themeasurement apparatus) through inversion. The drain currentand gate voltage are related by ID 10VG. When plotted as logIDversus VG, the linear I-V characteristic can be extrapolatedto a calc
23、ulated midgap current, IMG. By comparing the pre- andpost-irradiation characteristics, the midgap voltage shift, VMGcan be determined. The value of VMGis equal to Vot, whichis the voltage shift due to oxide trapped charge. The differencebetween the inversion voltage shift, VINV, and VMGis equalto Vi
24、t, which is the voltage shift due to interface traps. Thisprocedure is shown in Fig. 1 for a p-channel MOSFET.5. Significance and Use5.1 The electrical properties of gate and field oxides arealtered by ionizing radiation. The method for determining thedose delivered by the source irradiation is disc
25、ussed in Prac-tices E666, E668, E1249, and Guide E1894. The time depen-dent and dose rate effects of the ionizing radiation can bedetermined by comparing pre- and post-irradiation voltageshifts, Votand Vit. This test method provides a means forevaluation of the ionizing radiation response of MOSFETs
26、 andisolation parasitic MOSFETs.5.2 The measured voltage shifts, Votand Vit, can providea measure of the effectiveness of processing variations on theionizing radiation response.5.3 This technique can be used to monitor the total-doseresponse of a process technology.6. Interferences6.1 Temperature E
27、ffectsThe subthreshold drain currentvaries as the exponential of qB/kT, and other terms which varyas a function of temperature. Therefore, the temperature of themeasurement should be controlled to within 6 2C, since thetechnique requires a comparison of pre- and post-irradiationdata. At cryogenic te
28、mperatures, this test method may givemisleading results.46.2 Floating Body (Kink) EffectsFloating body effectsoccur in MOSFETs without body (substrate) ties. This testmethod should not be applied to a MOSFET without asubstrate or substrate/source contact.6.3 Short Channel EffectsTo minimize drain vo
29、ltage de-pendence on the subthreshold curve, a small drain measure-ment voltage is recommended but not necessary.6.4 Leakage CurrentBecause the MOSFET midgap cur-rent is below the capabilities of practical current-voltagemeasurement instrumentation, extrapolation of the subthresh-old swing is requir
30、ed for the determination of a MOSFETmidgap voltage. Extrapolation of ideal linear MOSFET sub-threshold current-voltage characteristics is unambiguous, be-cause of the constant subthreshold swing. An example of nearideal subthreshold characteristics is given in Fig. 2, where thesubthreshold current s
31、wing is relatively constant between 1011and 106A. Nonideal subthreshold characteristics, that areaberrations from the theoretical linear subthreshold swing, cancomplicate the subthreshold current swing extrapolation to themidgap voltage. For subthreshold characteristics that havemultiple subthreshol
32、d swings, the value of the midgap voltagewould be dependent on the values of the subthreshold currentfrom which the extrapolation is made. Nonideal subthresholdFIG. 1 Determination of Radiation Induced Voltage Shift forp-Channel MOSFETF996 11 (2018)2characteristics are caused by MOSFET leakage curre
33、nts thatcan be either independent of, or a function of, gate-sourcevoltage.6.4.1 Junction Leakage CurrentThis leakage current isfrom the drain to the substrate and is independent of gate-source voltage. Junction leakage current masks the actualMOSFET channel subthreshold current below the leakagecur
34、rent level. Junction leakage current is easily distinguishedfrom the channel subthreshold current as is shown in Fig. 2 bythe flat section of the drain current, ID, below 1011A. Thisfigure also shows the advantage of using the source current, IS, for extrapolation. The source current is not affected
35、 byjunction leakage so that a measure of the MOSFET channelcurrent is obtained to the instrumentation noise level. However,if there is not a separate source and substrate contact (forexample, power MOSFETs), the drain current must be used.Only the part of the subthreshold curve above the junctionlea
36、kage or instrumentation noise level should be used forextrapolation. A minimum of two decades of source or draincurrent above the leakage or noise is required for application ofthis test method.6.4.2 Gate LeakageGate leakage can be any combinationof leakage from the gate to source, drain, or substra
37、te.Typically this leakage will be a function of the gate-sourcevoltage. If gate leakage is greater than 1.0 A for anygate-source voltage, the test method should not be applied.Gate leakages less than 1.0 A can still cause nonidealsubthreshold characteristics. The minimum value of the sub-threshold s
38、ource or drain current used for extrapolation to themidgap voltage must be above any changes in the subthresholdswing that can be attributed to gate leakage. Plotting the log ofthe gate leakage along with log source and drain current on thesame graph, will aid in the determination of gate leakageeff
39、ects on the drain and source subthreshold swing.6.4.3 Edge Leakage CurrentMost microcircuit MOSFETsuse an open geometry layout so that ionizing radiation induceddrain to source leakage can occur in n-channel devices outsideof the intentional MOSFET channel. The effect of this edgeleakage on the subt
40、hreshold swing is dependent on the aspectratios and threshold voltages of the intentional and parasiticMOSFETs. The aspect ratio of the parasitic MOSFET wouldusually be much smaller than a standard width MOSFETlayout. Thus, when the MOSFET channel is in stronginversion, the channel current will typi
41、cally dominate.However, as the channel current is reduced, edge leakage cango from a minimal fraction to dominating the measured drainor source current if the parasitic MOSFET inversion voltage isless than the intentional MOSFET. This effect can be observedin the measured subthreshold characteristic
42、s as a deviationfrom the ideal linear subthreshold curve that is a function of thegate-source voltage. Examples of parasitic MOSFET induceddeviations from the ideal linear subthreshold swing are given inFig. 3 and Fig. 4.InFig. 3, the subthreshold swing changesfrom the initial swing near inversion t
43、o a much larger mV/decade swing. In Fig. 4, a more pronounced deviation isshown. The section of the subthreshold curve that should beused for extrapolation to the midgap voltage is shown in bothfigures. The upper section of the subthreshold curve above thelower current level deviations was used. Any
44、 lower currentchange in the subthreshold swing from the initial subthresholdswing below strong inversion should be considered a parasiticMOSFET induced deviation. Only the part of the subthresholdcurve above this deviation should be used for extrapolation asis shown in Fig. 3 and Fig. 4. Some n-chan
45、nel MOSFETs mayhave post-irradiation edge leakage sufficiently large to preventany observation of a subthreshold swing. The subthresholdcharge separation technique cannot be applied to thesesamples.Aminimum of two decades of source or drain currentabove any subthreshold swing deviation is required f
46、or appli-cation of this test method. Open and closed (annular) geometrylayouts can be used to separate edge leakage current from theMOSFET channel current.6.4.4 Backchannel and Sidewall Leakage in a SOIMOSFETIn a silicon-on-insulator (SOI) MOSFET, the back-channel leakage arises from a parasitic MOS
47、FET located at theinterface between the epitaxial silicon and the insulator. Side-wall leakages arise from the parasitic MOSFET formed at theedges of the intentional MOSFET. These parasitics distort thesubthreshold curve in the same manner as described in 6.4.3.FIG. 2 Near Ideal Subthreshold Charact
48、eristics from ann-Channel TransistorFIG. 3 Example of a Parasitic MOSFET Induced Deviation Fromthe Ideal Linear Subthreshold SwingF996 11 (2018)37. Apparatus7.1 To measure the subthreshold current-voltage character-istics of a MOSFET, the instrumentation required consists of,as a minimum, two voltag
49、e sources and four ammeters.7.2 The power supplies are used to apply voltage to the gateand drain of the MOSFET. The ammeters are used to measurethe gate, drain, source, and substrate currents.7.3 For MOSFETs that have a common source/substratecontact, only three ammeters are required.7.4 For a typical digital microcircuit MOSFET the voltagesources and ammeters should meet the specification given inTable 1.7.5 For a power, parasitic field oxide, or high voltage linearMOSFET, the maximum voltage requirement for the gate-source power
