Application of transient interferometric mapping

Outline• Motivation• Principle of Transient Interferometric Mapping (TIM)• Application example of TIM– Thermal breakdown mechanism in ESD protection devicesdue current filaments– Analysis of carrier plasma spreading in 90nm CMOS SCRESD protection device– Transient latch-up analysis in 90nm CMOS test chip– Failure analysis• Conclusions

MotivationExperimental access to internal device parameters (temperature,carrier concentration, current density, electric field) is important for: Finding critical places in devices - hot spots, thermo-mechanicalstress,..Device structure and performance optimization Verification of simulation results Calibration of simulation models Prediction of device failure thresholdThermal and high injection effects important in: power devices,electrostatic discharge (ESD) protection devices, etc...⇒ TIM method provides µm space and ns time resolutionand access to bulk properties from backside

Electrostatic discharge (ESD)Human Body Model (HBM)RelayswitchR=1.5kΩL1-10kVHVC=100pFDUT1-5Amps@100nsCatastrophic failure[Amerasekera & Duvvury, 1995]- ESD more and more important withscaling down technologies- higher power dissipation densities insmaller volumes higher temperaturesup to silicon melting point[Courtesy W. Stadler, Infineon]

Backside Transient Interferometric Mapping (TIM)IR laser, wavelength=1.3µm is transparent for SiΔϕdrainmicroscope objectivegateheatingsubstratePolishedchipbackside* Temperatureand carrier conc.variations⇓* Change inrefractive index⇓* Optical phaseshift Δϕ⇓* Interferometricdetection

General optical principle of TIMOptical phase shift (integral along the laser path):Δϕ4πλ() t = ΔT( z, t) + α Δn( z, t) + α Δp( z, t)∫⎧ dn⎨⎩dT[ ]np⎭ ⎬⎫ dzThermal contribution>0+Free-carrier contribution

Method is quantitative:APEX postprocessor of Synopsis allows calculation ofphase shift data from the simulated temperature and freecarrier distributions of device simulation (TCAD) DESSIS

Transient interferometric mapping (TIM) at TUVienna:* Scanning heterodyne interferometer + Michelson- 3ns and 1.5µm resolution- phase shift transients recorded at eachscanning position- repetitive stressing necessary forspatial imaging* 2D holographic interferometric method- 5ns and 3µm resolution- one or two 2D images recordedper single stress pulse- single event thermal imaging- wafer level probing possible

Scanning heterodyne interferometerlaser diodeλ=1310 nmω 1ω 2+microscopeobjectivexy-stage* 1.5µm space resolution* 3ns time resolutionAOMmirrorD.U.T.photodiodeexternalreferencemirrorIR observationcameraTLP testervf-TLP testerDMOS pulserMOS-switchSpatialdistribution:- periodicaldevice stressing- lateral devicescanningHVsourceFocused laser beam used Fürböck &, Microel. Rel. 40(2000)1365]

Scanning heterodyne interferometer: signal and phase shiftDetector signalPhase shift (rad)1.61.20.80.40.0ΔϕHeatingheatingnoheating0 200 400 600 800Time (ns)Detector signal:A sin[2Δωt+Δϕ(t)]* Time domain detection* Automated acquisition* FFT analysis* phase extractioninsensitive to samplereflectivity[Fürböck &, J. Elstat, 49(2000)195][M.Litzenberger &, IEEE TIM, 54(2005)2438]

2D TIM method: Phase extractionInterferogram:Unstressed Stressed[D.Pogany &, IEEE EDL, 23(2002)606]p-bodyAnodep+ n+n+ buried layern-epip-substrate⊕n+ sinkerCathodePhase extractionbased on FFT analysisTemperature-inducedphase shiftPhase(Stressed) - Phase(Unstressed)⇒

2D TIM methodImaging at two time instants during a single shotIRcamera 2IRcamera 1MonitorPCPulsecontrolDUTMOMLPBS L NPBSDETLaser 2 PBSLaser 1CT1 1kΩ50ΩOSCIL.Beam 1HVelectron.pulserBeam 2Electricalsignal path• orthogonally polarizedlaser beams• laser pulse duration5ns• relative laser pulsedelay 0 ns - 5 μs• phase distribution attwo time instantsduring single stresspulse- non-repetitivephenomena(destructive)[Dubec &, Microel.Reliab.44(2004)1793]

Model verification at high temperatures by TIMESD protection diode : comparisom TIM vs. TCAD simulationUp to 1100K models for impact ion. coeff. verified experimentally[S. Reggiani et al. I3E EDL, vol.26 2005, p.916]

Current filament dynamics in ESD protection devicesPhase shift –measuredAnode⊕p+ n+n-epip-bodyn+ buried layerp-substraten+ sinkerCathodeP2D – extractedpower density130 nsFilament hasbeen created130 ns200 nsFilamentmoves to left200 ns290 nsFilamentreflects fromdevice corner290 ns530 nsFilamentmoves back530 ns-1 rad4 rad-3030 mW/μm 2[Dubec &, Microel.Reliab. 44(2004)1793]

Instantaneouspower extractionfrom TIMmeasurementsFilament movement alongthe device widthNpn ESD prot. deviceanodecathode+Device lengthDevice widthCalculated:P 2D ≈curr.densityp+ n+p bodyIavlaser beamn- epin+sinkern+ buried layerDevice widthp - substrateMeasured:Δϕ:memoryeffectDevice lengthBy 2D scanning[Pogany &, App.Phys.Lett,81(2002)2881]

Second breakdown due to stopped current filaments10.90.8w200, 600-620 nsw200, 70-90 nsTLP Current (A)0.70.60.50.40.30.20.100 10 20 30 40 50 60TLP Voltage (V)p-bodyAnodep+ n+n+ buried layern-epip-substrate⊕n+ sinkerCathodeVoltage (V)252015105t TBOptimized structures00 200 400 600 800 1000time (ns)Thermal breakdown (TB) occurs when filament reaches an alreadypreheated region (edge, or start position) improving t TB[D. Johnsson &, IRPS08, p.240]

TLU analysis in 90nm CMOS structures* Invertor sensitivity toLatch –up is studued* Injector diode emulatessubstrate current injectionDetector Voltage3V0V0µs 1µs 2µs 3µsPhase [mrad]0-500µs 1µs 2µs 3µsLaser[K.Domanski et al. EOS/ESD’07, p.347]

Carrier an heat distribution during TLU event:effect of guard rings studiedGuardRingfloating:GuardRing3V:[K.Domanski et al.EOS/ESD’07, p.347]-200mApulse of1623ns• Carrier diffusion length can be experimentally determinedTU-Wien ≈100µm (≈1µs) → calibration of simulator• Guard ring effect demonstrated –still carrent via substrate

90 nm CMOS SCR study: spreading of the on statet1t2 >t1P-well, P-substrateN-welln+p+n+YZp+t3 >t2n+p+-electron-hole plasma spreads with timeto sides and to substrate- heating follows with a delay the currentflowDensity of current inside filamentt1: t2: t3:J1 J2

ESD failure detection using 2D TIM method– rough position detection in a large field of view2 mW ~ 3 mrad FOV1.6x1.3 mmIR imageInterferogram difference2 mW ~ 3 mradStroboscopicdetection usingrepetitivepulses +stabizedMichelsoninterferometerIR imageTesting on npn transistorInterferogram differenceFOV3x2.5 mm[V.Dubec et al. , Microel. Reliab, 47(2007)1549]

Scanning TIM technique for failure analysis- metal short detection[V.Dubec et al. , Microel. Reliab, 47(2007)1549]2D scanLaserω ω+Ω 1ω+Ω 2DETAOM+L.O.Microscope= PhaseDUTScan area1x1 mm(metal short)Ω 1t - Ω 2t + Δϕ Ω 1t - Ω 2t Δϕ• power resolution up to 50 μW• spatial resolution 2 μm• comparable to standard FA methods(e.g. TIVA)•possible to combine FA with standardTIM for ESD analysisSingle beam scan0.4Differential scanPhase (rad)0.30.20.10.0IR image-800 -600 -400 -200 0 200X-position (μm)

ConclusionsTIM :– free carrier and thermal dynamics can be detected with ns timeand µm space resolution– understanding device physics and for device layout optimisation- used for calibration and verification of device simulation modelsunder high current and high temperature conditions- failure analysis application- other applications include thermal mapping of GaN HEMTs,lasers [J.Kuzmik &, APL 2003, IEEE TED 2005, SSE 2006,…]