Radiation Effects in Emerging Materials - Institute for Space and ...

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Radiation Effects in Emerging Materials - Institute for Space and ...

May , 2008Radiation Effects on Emerging Electronic Materials andDevicesRadiation Effects in Emerging MaterialsOverviewLeonard C. FeldmanVanderbilt UniversityAndRutgers University


Topics of InterestBasic radiation interaction with electronicmaterials-review, educationalAlternate Dielectrics and Gate Stacks-in allaspects-growth, spectroscopy, radiation effects amajor emphasis on nano-scale structure--SiGe devices and other “alternate substrates”(Ge, InGaAs, SiC)Strained silicon


Basic radiation interaction withelectronic materialsmodificationsat the nanoscaleNanoscale:Basic theory of e-h pair production,particularly ε, the average energy requiredfor e-h pair creation, is based on bulkconcepts, including bulk density of states.The nanoscale thicknesses, and the newunderstanding of nanoscale effects callsfor re-examination of these concepts.ΔV=Q/C=N e {(dE/dx) t ox /ε} /CMOS SchematicGateSioxidemetalε= average energy/e-h pairN e = number of electrons penetrating the dielectric


ε= 2.6E g + Kε vs. E gShockley-Klein


CVS and irradiation - 7.5 nm/1nm7.5 nm HfO 2Dielectric stackBias stress at -2 V1 nmSiO 2Hole injection- 2V bias stressHfO 2SiO 2E CTiNE iBiased irradiation at -2 VE fp-SiE VAt 10 Mrad(SiO 2 ), ΔN t = ~ 3.8 x 10 12 cm -2AccumulationDixit et al., IEEE TNS, vol. 54, p. 1883, 2007Ph. D. Dissertation Defense24 th March, 2008


Rutgers CMOS Materials AnalysisUse high resolution characterization methods to: Determine composition, structure and electronic propertiesgate stacks that use new (post-Si) materials Help determine physical and chemical nature of radiationinduced defectsSurface/interface analysis:• Ion scattering: RBS, MEIS, NRA, ERD –composition, crystallinity, depth profiles, H/D• Direct, inverse and internal photoemission –electronic structure, band alignment, defects• Scanning probe microscopy – topography,surface damage, electrical defects


Motivation: Help develop a fundamentalunderstanding and control of radiation induceddefects in future CMOS materials.Rutgers team uses high resolution characterization tools to:• Determine composition, structure and electronic properties ofgate stacks that use new (post-Si) materials• Help determine physical and chemical nature of pre-existing andradiation induced defectsExperimental studies of High-k on Ge and III-V substrates:• Composition and depth profiling – MEIS, XPS, RBS…• electronic structure – PES, IPE, optical and electrical methods…


S-passivated film Fermi levels partiallypinned; after HfO2 growth, little pinning.Conduction and valance band offsetsmeasured; agree with literature.S- passivated n-GaAsS- passivated n-GaAsHfO 2E cE c0.35-0.4 eVE F1.9 eVE F1.4 eV1.4 eV3.9 eVE v~2.3-2.4 eVE vS- passivated p-GaAsS- passivated p-GaAsHfO 2E cE c1.4 eV1.4 eVE vE F0.35-0.4 eVE F~2.3-2.4 eV2.5 eVE v


HfO 2 sample detailsGateSource Drain Bodyn + n + p +p-wellp-substrateSamplesHfO 2based nMOSFETExperimental• State-of-the-art samples, SEMATECH, Inc. • 10 keV X-rays, RT irradiation• 65 nm technology node• Function of dose• nMOSFETs with W/L = 10µm/0.2µm• Function of bias• t phys= 7.5 nm and 3.0 nm• Characterization done using(EOT = 1.2 nm and 0.5 nm)I-V measurements• SiO 2interlayer (~ 8Å)


C-V - Comparison (Theory &Measured)1C eff=1C HfO2+1C SiO2 HfO 2deposition + PDA at 700 °C Intermixing issues Interlayer sub-stoichiometric κ effreduces!C HfO2C SiO2HfO 2SiO 2κ ~ 10κ ~ 750% Si20% SiPh. D. Dissertation Defenseat % HfCallegari et al., JAP, v.90,p. 6466, 200124 th March, 2008


Materials analysis - HfO 2 /SiO 2 IL/SiRBS/Channelingt HfO2& t SiO2MEIS t HfO2, t SiO2 & Si in HfO 2O peak(HfO 2 /SiO 2 )XRRq c critical angle1.8 MeV He +Scattering angle 175º channelHf peakSi surfacepeakt HfO22000 E 0 =130.0KeVIncident angle = 0 o Scattering angle = 125.3 o Yield [a.u.]150010005000COSi10X100 105 110 115 120 125 130Energy [KeV]SimulationExperimentSi surfaceSi surf peakC-V t HfO2, t SiO2 & Si in HfO 2HfFringesDixit et al., manuscript to be submitted to JAP, 2008Ph. D. Dissertation Defense24 th March, 2008


RBS/MEIS - HfO 2 /SiO 2 IL/SiHfO 2SiO 2‘Hf’ concentration% χ min for Si ~ 4 %Samples‘Hf’ expected(10 15 at/cm 2 )‘Hf’ RBS(10 15at/cm 2 )‘Hf’ MEIS(10 15at/cm 2 )3nm/1nm8.248.29 ± 0.038.327.5nm/1nm20.620.2 ± 0.00519.953nm/2nm8.248.10 ± 0.037.97.5nm/3nm20.620.7 ± 0.00519.51Feldman et al., Material analysis by ion-channeling:Submicron crystallography, Academic Press, NY, 1982


RBS/MEIS - HfO 2 /SiO 2 IL/Si‘O’ concentrationSamples‘O’ expected‘O’ RBS‘O’ MEIS(10 15 at/cm 2 )(10 15 at/cm 2 )(10 15 at/cm 2 )3nm/1nm21.2821.9 ± 0.222.377.5nm/1nm46.045.5 ± 0.236.823nm/2nm25.2824.2 ± 0.220.167.5nm/3nm54.455.1 ± 0.355.81Interlayer ‘O’ concentrationSamples3nm/1nmIL ‘O’ expected(10 15 at/cm 2 )4.84IL ‘O’ RBS(10 15 at/cm 2 )5.32 ± 2.017.5nm/1nm3nm/2nm7.5nm/3nm4.848.8013.25.10 ± 2.428.02 ± 2.3213.6 ± 2.92


MEIS - HfO 2 /SiO 2 IL - 3nm/1 nmNo Anneal700 C NH 3 Anneal2000 E 0 =130.0KeVIncident angle = 0 o Scattering angle = 125.3 o Yield [a.u.]15001000OSi10XSimulationExperimentHfYield [a.u.]200015001000E 0=130.0KeVIncident angle = 0 o Scattering angle = 125.3 o OSi10XExperimentalSimulationHf500CSi surf500Surf. C NSurf. Si0100 105 110 115 120 125 130Energy [KeV]0100 105 110 115 120 125 130Energy [KeV]ElementConcentration ×10 15 [atoms/cm 2 ]ElementConcentration ×10 15 [atoms/cm 2 ]Hf8.32Hf7.90Si3.87O20.16O22.37NSi (surface)3.680.97


Total dose results comparisonKey results 3 nm HfO 2 /2 nm SiO 2• IL O leaching 7.5 nm HfO 2(exposure t at higher temp. growth a,b )• I-V sweeps modify the charge (~ 50%)(border traps in the SiO 2IL c )• Residual V Tafter stabilization(traps in HfO 2and/or away frominterface)Irradiation Bias ~ -2 MV/cma Bersuker et al., JAP, vol. 100, p. 094108, 2006,bRyan et al., APL, vol. 90, p. 173513, 2007,c Fleetwood et al., IEEE TNS, vol. 39, p. 269, 1992.Dixit et al., manuscript to be submitted to APL, 2008Ph. D. Dissertation Defense24 th March, 2008


A New Dielectric DegradationPhenomenon in High-k Devices!Vth /Vth0 (%)1512-3 0369-12-9-6-15-18V STRESS= 3.0 VNo dischargeAfter dischargeClosed: !V thOpen: !gm10 0 10 1 10 2 10 3 10 4Stress time (sec)100101!gm/gm0 (%)Positivechargebuildupcaused byelectroninjectionstressGennadi Bersuker, SEMATECH


• Hole traps are generated inthe interfacial layer ofnMOS high-k devicesduring inversion stress;tentatively attributed to Nspecies in high-k stack may affect evaluation ofradiation-induceddegradation mechanismTiN HfO 2SiO 2 SiHole trap location

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