Application of transient interferometric mapping (TIM

D.Pogany, TU Vienna, Toulouse 2009

Application of transient interferometric mapping (TIM) technique for analysis of ns-time scale thermal and carrier dynamics in

ESD protection devices

D. Pogany, S. Bychikhin, M. Heer, W. Mamanee, V. Dubec, E. GornikInstitute for Solid State Electronics, Vienna University of Technology

D. Johnsson, K. Domanski, K. Esmark, W. Stadler, H. Gossner, M. StecherInfineon Technologies, Am Campeon, Neubiberg, Germany

The work was performed within EU Medea+ projects SIDRA (T104) and SPOT2 (2T205)and EU FP5 project DEMAND (IST2000-30033)


• Motivation• Principle of Transient Interferometric Mapping (TIM)• Application example of TIM

– Thermal breakdown mechanism in ESD protection devices due current filaments

– Analysis of carrier plasma spreading in 90nm CMOS SCR ESD protection device

– Transient latch-up analysis in 90nm CMOS test chip– Failure analysis

• Conclusions

Outline


MotivationExperimental access to internal device parameters (temperature, carrier concentration, current density, electric field) is important for:

Finding critical places in devices - hot spots, thermo-mechanical stress,..

Device structure and performance optimization

Verification of simulation resultsCalibration of simulation modelsPrediction of device failure threshold

Thermal and high injection effects important in: power devices, electrostatic discharge (ESD) protection devices, etc...

⇒ TIM method provides µm space and ns time resolution and access to bulk properties from backside


Electrostatic discharge (ESD)Human Body Model (HBM)

1-10kV

1-5Amps@100ns

[Courtesy W. Stadler, Infineon]

Catastrophic failure

HV

Relayswitch R=1.5kΩ

C=100pF

L

DUT

[Amerasekera & Duvvury, 1995]

- ESD more and more important with scaling down technologies- higher power dissipation densities in smaller volumes higher temperaturesup to silicon melting point


* Temperatureand carrier conc.

variations⇓

* Change inrefractive index

⇓* Optical phase

shift Δϕ⇓

* Interferometricdetection

substrate

drain

Polishedchipbacksidemicroscope objective

gate

heating

Δϕ

Backside Transient Interferometric Mapping (TIM)IR laser, wavelength=1.3µm is transparent for Si


General optical principle of TIM

( ) ( ) ( ) ( )[ ]∫ ⎭⎬⎫

⎩⎨⎧ Δα+Δα+Δ

λπ

=ϕΔ dzt,zpt,znt,zTdTdn4t pn

Optical phase shift (integral along the laser path):

Thermal contribution>0

Free-carrier contribution<0

Both components can bedistinguished according to

the sign and different time scales

Thermal component is dominant at high dissipated powers

+

Δϕ

Free-carrier

Temperature

Time

Sum T+FC

[Goldstein &,Rev.Sci. In. 64(1993)3009, D.Pogany & IEEE TED 49(2002)2070]


Method is quantitative:

APEX postprocessor of Synopsis allows calculation of phase shift data from the simulated temperature and free carrier distributions of device simulation (TCAD) DESSIS


Transient interferometric mapping (TIM) at TU Vienna:

* 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 recorded

per single stress pulse- single event thermal imaging- wafer level probing possible


Scanning heterodyne interferometer

IR observationcameramicroscope

objective D.U.T.

AOM

laser diode=1310 nmλ

+ω 1

ω 2 external referencemirror

MOS-switchxy-stage

mirror

photo diode

TLP testervf-TLP testerDMOS pulser

HVsourceHVsource

* 1.5µm space resolution* 3ns time resolution

Spatial distribution:

- periodical device stressing

- lateral device scanning

Focused laser beam used Fürböck &, Microel. Rel. 40(2000)1365]


Scanning heterodyne interferometer: signal and phase shiftD

etec

tor s

igna

l

noheating

heatingΔϕ

Heating

0 200 400 600 8000.00.40.81.21.6

Time (ns)

Phas

e sh

ift (r

ad)

Detector signal:

A sin[2Δωt+Δϕ(t)]

* Time domain detection* Automated acquisition* FFT analysis* phase extraction insensitive to sample reflectivity

[Fürböck &, J. Elstat, 49(2000)195]

[M.Litzenberger &, IEEE TIM, 54(2005)2438]


2D TIM method: Phase extraction

Phase extraction based on FFT analysis

Phase(Stressed) - Phase(Unstressed) ⇒

Temperature-inducedphase shift

StressedInterferogram:

Unstressed

p-body

n+ s

inke

r

n+ buried layer

p-substrate

n-epip+ n+

⊕ CathodeAnode

[D.Pogany &, IEEE EDL, 23(2002)606]


2D TIM method

DUT

NPBS

IRcamera 2

PC

HVelectron.

pulser

1kΩ

50Ω

OSCIL.

M

Beam 2Electricalsignal path

L

L

MO

Monitor

CT1

DET

Lase

r 1

Laser 2 PBS

IRcamera 1

PBS

Beam 1

Pulsecontrol

• orthogonally polarized laser beams

• laser pulse duration 5ns

• relative laser pulse delay 0 ns - 5 μs

• phase distribution at two time instants during single stress pulse

- non-repetitive phenomena (destructive)

[Dubec &, Microel.Reliab. 44(2004)1793]

Imaging at two time instants during a single shot


Model verification at high temperatures by TIM

[S. Reggiani et al. I3E EDL, vol.26 2005, p.916]

Up to 1100K models for impact ion. coeff. verified experimentally

ESD protection diode : comparisom TIM vs. TCAD simulation


4 rad-1 rad

130 ns

530 ns

290 ns

200 ns Filament moves to left

Filament has been created

Filament reflects from device corner

Filament moves back

130 ns

530 ns

290 ns

200 ns

30 mW/μm2-30

P2D – extracted power density

Phase shift –measured

[Dubec &, Microel.Reliab. 44(2004)1793]

Current filament dynamics in ESD protection devices

p-body

n+ s

inke

r

n+ buried layer

p-substrate

n-epip+ n+

⊕ CathodeAnode


Instantaneous power extraction from TIM measurements

Filament movement along the device width

Measured: Δϕ: memory effect

Calculated:

P2D ≈

curr.

density

By 2D scanning

Device width

p - substrate

n+ buried layer

p body

p+n+sinker

n- epi

+

laser beam

anode cathode

n+

Iav

Npn ESD prot. device

[Pogany &, App.Phys.Lett,81(2002)2881]

Dev

ice

leng

th

Device length

Device

widt

h


Second breakdown due to stopped current filaments

[D. Johnsson &, IRPS08, p.240]

Thermal breakdown (TB) occurs when filament reaches an already preheated region (edge, or start position) improving tTB

0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

TLP Voltage (V)

TLP

Cur

rent

(A)

w200, 600-620 nsw200, 70-90 ns

0 200 400 600 800 10000

5

10

15

20

25

Vol

tage

(V)

time (ns)

p-body

n+ s

inke

r

n+ buried layer

p-substrate

n-epip+ n+

⊕ CathodeAnode

Opt

imiz

ed s

truct

ures

tTB


TLU analysis in 90nm CMOS structures

0µs 1µs 2µs 3µs0V

3V D

etec

tor V

olta

ge

0µs 1µs 2µs 3µs

-50

0

Pha

se [m

rad]

Laser[K.Domanski et al. EOS/ESD’07, p.347]

* Invertor sensitivity to Latch –up is studued* Injector diode emulates substrate current injection


TU-Wien

Carrier an heat distribution during TLU event: effect of guard rings studied

• Carrier diffusion length can be experimentally determined ≈100µm (≈1µs) → calibration of simulator

• Guard ring effect demonstrated –still carrent via substrate

GuardRingfloating:

GuardRing 3V:

-200mA pulse of 1623ns

[K.Domanski et al. EOS/ESD’07, p.347]


N-well

P-well, P-substrate

p+

p+

p+

n+

n+

n+

Z

Y

t1

t1: t2: t3:

t2 >t1

t3 >t2

J1 J2<J1 J3<J2

Density of current inside filament

90 nm CMOS SCR study: spreading of the on state

-electron-hole plasma spreads with time to sides and to substrate- heating follows with a delay the current flow

[K.Esmark et al, IRPS08, p.247]


ESD failure detection using 2D TIM method – rough position detection in a large field of view

2 mW ~ 3 mrad FOV 1.6x1.3 mm

FOV 3x2.5 mmIR image Interferogram difference

2 mW ~ 3 mrad

[V.Dubec et al. , Microel. Reliab, 47(2007)1549]Testing on npn transistor

IR image Interferogram difference

Stroboscopic detection usingrepetitive pulses +stabizedMichelson interferometer


Scanning TIM technique for failure analysis- metal short detection

• power resolution up to 50 μW• spatial resolution 2 μm• comparable to standard FA methods (e.g. TIVA)•possible to combine FA with standard TIM for ESD analysis

AOM

DUT

DET + L.O. = Phase

ω ω+Ω1 ω+Ω2

Ω1t - Ω2t + Δϕ Ω1t - Ω2t Δϕ

LaserMicroscope

IR image

-800 -600 -400 -200 0 200

0.0

0.1

0.2

0.3

0.4

Pha

se (r

ad)

X-position (μm)

Single beam scanDifferential scan

2D scan

Scan area1x1 mm

(metal short)

[V.Dubec et al. , Microel. Reliab, 47(2007)1549]


Conclusions

TIM :

– free carrier and thermal dynamics can be detected with ns time and µm space resolution

– understanding device physics and for device layout optimisation

- used for calibration and verification of device simulation models under 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,…]

Documents

Application of transient interferometric mapping (TIM