MICROELECTRONICS

FAILURE ANALYSIS LABORATORYTHALES Microelectronics S.A.

THERMAL LASER STIMULATION(TLS / OBIRCH / TIVA)

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TLS in the FA flowI.C. FA flow

Electrical diagnostic

Defect localization

Physical analysis

Current related defects

Emission microscopy

Thermal Laser Stimulation

– Ileakage metallic shorts

– Ileakage junctions– Ileakage oxides

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TLS PrinciplesLASER

λ = 1,3 µm• Heating• No e-h pair

generation

High absorption in:– Metals– Polysilicon– Highly doped silicon

16Aluminium cm10x1,1 −=α

Valence band

Conduction band

Ephoton < Eb.g.

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Laser Heating of Metals

Electric current density :

↑ T° → Current variation∇ T°→ Additional current

( )[ ]TQ ∇−+≅ Ej σ

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A. Resistance Variation

( ) TSLR TTCR ∆−=∆ δαρ 20

αTCR → Temperature Coefficient of Resistivity

δT → Coefficient of Thermal linear dilatation

Aluminium

αTCR = 4,29x10-3

δT = 2,36x10-5 ( )V RRI 2∆−=∆

Current Source (TIVA)

IRV ⋅∆=∆Voltage Source (OBIRCH)

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B. Electromotive Force Generation

T > T0

T0

Laser

T0 M 1 M 2

Q → Thermoelectric power orSeebeck coefficient

Q12 → Relative Thermoelectric power

( )( ) ( )01202112 TTQTTQQV −=−−=

Materials Q12 (µV/oC)

Al / W 7,0

-121

Al / n+ Si(1020cm-3) -105

Al / n+ Poly

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TLS Model

Length = 120µm

Model: 1µm Al line, Gaussien Laser

2 cases:- Transversal- Longitudinal

1µm0.5µm1µm

AlSiO2

Silicon

1µm

4µm

10µm

Parameters:Tini: 25oCPlaser: 100mWRlaser: 0,65µmVfast: 1,23m/sVslow: 0,00768m/s

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A. Transversal Case• Rapid thermal equilibrium and heat dissipation• Hottest temperature occurs at laser spot

Slowest scanning speed

253545556575

0 1 2 3 4 5 6 7 8 9 10 11 12 13Position (µm) Elapsed time (µs)

T (°

C)

transversal slowtransversal fast

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B. Longitudinal Case

• Thermal equilibrium reached after 10µs

Slowest scanning speed

25

35

45

55

65

75

0,0E+00 5,0E-06 1,0E-05 1,5E-05 2,0E-05Time (s)

T (°C

) longitudinal slowlongitudinal fast

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Temperature CalculationAt thermal

equilibrium:

Thermal spreading limited to ~ 30µm

Temperature varies linearly with laser

power

∆Tmax = 0.55oC/mW

25

35

45

55

65

75

-20 -10 0 10 20Position from the laser center (µm)

T (°C)trans. slowtrans. fastlong. slowlong. fast

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Resistance Calculation

Laser Power(mW)0 20 40 60 80 100

Res

ista

nce

Varia

tion

(Ω)

0,00

0,05

0,10

0,15

0,20∆R = 0,17Ω

∆Rmax = 1,7 mΩ/mW

( )0MoyTCR0 TTS

LR −αρ

=∆

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Model Conclusion

Precise localizationThermal diffusion < 30µm

Tmax at center of line and laser beam

Localization of defects and lines submitted to Ileakage∆R 1/∝ Section∆V ∝ Ileakage

Localization of junctions and interface defectsQ12 or ∆T

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TLS System Requirements• Laser scanning microscope (LSM)

– Gaussian laser of λ > 1,1µm• Acquisition and imaging system• Biasing and amplification scheme :

Techniques Inventor Bias

OBIRCHCC-OBIRCH

TIVATBIPXIVA

NikawaNikawa

Cole

PalaniappanFalk

V

I

V

SEI Cole

Amplifier

I / None

I

V

V

V

TLS

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Configurations

I.C.

AMPLIV / V

I.C.

AMPLII / V

OBIRCH

I.C.

AMPLIV / V

TIVA• Other configurations:

– Inductance (TBIP / XIVA)– No bias (SEI)

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TLS on Test StructuresAl line

Poly line

N+ resistance

No bias (SEI)

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TLS Case Study #1• Failed CMOS IC

– I ~ 2mA @ 5V• No emission• Front-side

Metal short (M1-M2)

TLS 200X

TLS 5X

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TLS Case Study #2• Failed BICMOS IC

– I > 100 µA (I/O)• Backside

– 4 metal levels

TLS (20x)

W short (Drain-Source)EMMI (20x)

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TLS Case Study #3• Failed CMOS IC

– I ~ 2 mA @ 3V • Front-side

TLS (20x)

TLS (20x)

Metal short (M2-M3)

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TLS Case Study #4• ESD failed commercial ICs

– HBM and MM stressed• Front-side

– No bias applied (SEI)SEI (200x)

SEI (50x)

Molten Si/Al filament

Molten Sispike

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TLS Case Study #5• GaAs failed ASICS

– I ~ 50 µA @ 3V • Front-side

TLS (100x) Gold filament

Defects induced by CDM type ESD stress

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Conclusion : TLS Application Field

Thermal Laser

StimulationSignature Defect type Material

Current lines Shorts

ESD defects Voids

No Bias

Ileakage >1µA

All circuits Comparison

Bias

ESD defects Interface defects

AI, W, Au, PolySi,

Doped Si, Amorph. Si

Metal / Metal Metal / Si

Metal / Poly SiMelted Si / Si