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U of U PHYS 5739 - EDS Mapping

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11EDS MappingIan HarveyFall 2008p.2Practical Electron MicroscopyCharacteristic X-ray generationFrom: Energy Dispersive X-ray Microanalysis, An IntroductionKevex Corp. 19882p.3Practical Electron MicroscopyX-ray generation source (sim) Electron Microscopy“X-ray Resolution” effects Electron MicroscopyX-ray detection Li-drifted Si (or h.p. Ge) crystal: Photoelectric effect # of electron / hole pairs α X-ray energy Charge pulse converted to V at FET CHIP LED switched on to reset saturated FET (deadtime)A Guide to Energy Dispersive X-Ray Analysisp.6Practical Electron MicroscopyOptical Feedback for FET resetA Guide to Energy Dispersive X-Ray Analysis Counting time = “live time” Reset time = “dead time” (all pulses rejected) For increasing beam current, count rate peaks andfalls off as dead-time increases4p.7Practical Electron MicroscopyResolution vs. count ratetradeoff EDS system sorts as well as counts X-rayevents, hence total count rate produced ismuch lower than that for WDS system To increase the count rate capability,shorten the time constant of the mainamplifier But at the sacrifice of resolution For many SEM and TEM application,count rate are low and a 10 µs timeconstant is used for highest resolutionp.8Practical Electron MicroscopyEDS: gaussian peak shapes E=hν-(KeV energy ofejected core electron) -(eV work function ofthousands of ejectedvalence electrons) FWHM α (C2E + N2)1/2 C= cons f(work funct) E= photon energy N= amplificationnoiseGoldstein et al. Scanning Electron Microscopy and X-Ray Microanalysis, 3rd ed. Klewer Academic Press5p.9Practical Electron MicroscopyX-ray spectrumdepends on VaccA Guide to Energy Dispersive X-Ray Analysisp.10Practical Electron MicroscopyAnother reason to keep thevacuum clean…Goldstein et al. Scanning Electron Microscopy and X-Ray Microanalysis, 3rd ed. Klewer Academic Press6p.11Practical Electron MicroscopyCare for quantitative analysis Assumptions: Flat polished sample Homogeneous within sampling region Calculations not simply ratio of intensities: Peaks may overlap (reason for WDX) Elements backscatter differently due to different density(producing different x-ray yields) Energy losses of incoming beam produce different x-raygeneration distributions for different elements Re-absorption of X-rays plays a role (Z-dependent) Some re-absorbed X-rays produce other X-rays (fluorescence) “Φρz” and “ZAF” corrections…Goldstein et al. Scanning Electron Microscopy and X-Ray Microanalysis, 3rd ed. Klewer Academic Pressp.12Practical Electron MicroscopyFigure 10.5er.3WDS: “sharp” peak shapes E=hν=hc/λ λ = 2d sin θ Counts are “digital”according to angularposition of crystalspectrophotometer Only collect x-rays ofthe one energy at agiven position ==>SLOW Superior for quant--“microprobe”Goldstein et al. Scanning Electron Microscopy and X-Ray Microanalysis, 3rd ed. Klewer Academic Press7p.13Practical Electron MicroscopyEDS or WDS:count the eventswithin a givenpeak “window”and map beamposition wheneach eventoccurs…A Guide to Energy Dispersive X-Ray Analysisp.14Practical Electron MicroscopyMapping…Because most of your samples are NOTflatsmooth / polishedhomogeneous8p.15Practical Electron MicroscopyTrading peak resolution fordata collection rates …A Guide to Energy Dispersive X-Ray Analysisp.16Practical Electron Microscopy9p.17Practical Electron MicroscopyTi Sub ionpump filamentp.18Practical Electron Microscopy“Hoar frost”: Take a nicepicture first…10p.19Practical Electron MicroscopyUse abackgroundwindowp.20Practical Electron Microscopy…after letting itrun for ~10minutes11p.21Practical Electron Microscopyp.22Practical Electron Microscopy12p.23Practical Electron Microscopysetupp.24Practical Electron Microscopy“Collect Maps”13p.25Practical Electron Microscopyp.26Practical Electron MicroscopyEnd collection,release ext14p.27Practical Electron Microscopyp.28Practical Electron Microscopy15p.29Practical Electron Microscopyp.30Practical Electron Microscopy16p.31Practical Electron Microscopyp.32Practical Electron Microscopy17p.33Practical Electron Microscopyp.34Practical Electron MicroscopyHow to analyze thin organic film?• Drop Vacc• Tilt the sampleRun at hi Vacc to identify all peaks• look for relevant L, M• do you need better “resolution”?18p.35Practical Electron MicroscopySEM (BSE) view of gross residual BCB (DOA)BSE (Z-sensitive) image shows dramatic contrast between organic(dark), primary Sn phase (grey), and primary Pb phase (white)p.36Practical Electron MicroscopyMiscellaneous Failure Mechanisms:Assembly Solderability 5x5 750/500 TC test First failure at ~150 cycles (Ni/Au only) Catastrophic failure rate on affected boards Unknown source of process sensitivitySolder lift-off from padAdjacent good pad19p.37Practical Electron MicroscopyEDS Maps of a Typical Pad Interface(Where-n-tar-blazes did the Cu come from??)BSE image Ni map Cu mapp.38Practical Electron MicroscopyTypical Ni/Au device(post-polish / 50% nitric; 3 min. decorative etch)←Etched bulk eutectic solder←Cu/Sn intermetallic←Columnar Ni grains←Etched Cu pad20p.39Practical Electron MicroscopyEDS Maps of a Failed Pad Interface(note lack of Cu/Sn intermetallic)p.40Practical Electron MicroscopyXRF: X-Ray Fluorescence21p.41Practical Electron MicroscopyXRF:•High Sensitivity vs. SEM-based•”Bulk” analysis technique•Lower spatial resolution (mm-mapping)•non-vacuum or low vacuum•quantitation; liquids possibleReduced backgroundp.42Practical Electron MicroscopyMicrospot XRF (June)22p.43Practical Electron MicroscopySpectral Mapping - BoneFossilizationFeNaKSiPp.44Practical Electron MicroscopyMap Image Overlays: BoneFossilizationFe – RedK – BlueSi –YellowP – GrayNa

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