THALES Microelectronics S.A. FAILURE ANALYSIS LABORATORY
THERMAL LASER STIMULATION (TLS / OBIRCH / TIVA)
MICROELECTRONICS
2
TLS in the FA flow I.C. FA flow Electrical diagnostic
Current related defects Emission microscopy
Thermal Laser Stimulation
– Ileakage junctions – Ileakage oxides
– Ileakage metallic shorts
Defect localization Physical analysis MICROELECTRONICS
3
TLS Principles LASER λ = 1,3 µm
Conduction band
• Heating • No e-h pair generation
Ephoton < Eb.g. Valence band
High absorption in: – Metals – Polysilicon – Highly doped silicon MICROELECTRONICS
α Aluminium = 1,1x10 cm 6
−1
4
Laser Heating of Metals Electric current density :
j ≅ σ[E + Q (− ∇T )] ↑ T° → Current variation ∇ T° → Additional current MICROELECTRONICS
5
A. Resistance Variation
∆R =
ρ0L S
(α TCR − 2δ T )∆T
Aluminium αTCR = 4,29x10-3 δT = 2,36x10-5 MICROELECTRONICS
αTCR → Temperature Coefficient of Resistivity δT → Coefficient of Thermal linear dilatation
Current Source (TIVA)
∆V = ∆R ⋅ I Voltage Source (OBIRCH)
(
)
∆I = − ∆R R V 2
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B. Electromotive Force Generation Laser
T0
M1
M2
T0
T > T0
V12 = (Q1 −Q2 )(T −T0 ) =Q12(T −T0 ) Q→
Thermoelectric power or Seebeck coefficient Q12 → Relative Thermoelectric power
MICROELECTRONICS
Materials
Q12 (µV/oC)
Al / W
7,0
Al / n+ Poly
-121
Al / n+ Si (1020 cm-3)
-105
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TLS Model 1µm
Parameters: Tini: 25oC Plaser: 100mW Rlaser: 0,65µm Vfast: 1,23m/s Vslow : 0,00768m/s
1µm Al SiO2
Silicon
10µm
0.5µm 1µm
- Transversal - Longitudinal
4µm
Length = 120µm
Model: 1µm Al line, Gaussien Laser MICROELECTRONICS
2 cases:
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A. Transversal Case • Rapid thermal equilibrium and heat dissipation • Hottest temperature occurs at laser spot 75
T (°C)
65
transversal slow transversal fast
55 45 35 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13
Slowest scanning speed
MICROELECTRONICS
Position (µm) Elapsed time (µs)
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B. Longitudinal Case • Thermal equilibrium reached after 10µs 75
T (°C)
65 55 45
longitudinal slow longitudinal fast
35 25 0,0E+00 5,0E-06 1,0E-05 1,5E-05 2,0E-05
Time (s)
Slowest scanning speed
MICROELECTRONICS
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Temperature Calculation trans. slow trans. fast long. slow long. fast
75
T (°C)
65 55
At thermal equilibrium: Thermal spreading limited to ~ 30µm
45 35 25 -20
-10 0 10 20 Position from the laser center (µm)
MICROELECTRONICS
Temperature varies linearly with laser power
∆Tmax =
o 0.55 C/mW
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Resistance Calculation Resistance Variation (Ω)
0,20
∆R = 0,17Ω
0,15 0,10
∆Rmax = 1,7 mΩ/mW
0,05 0,00 0
20
40
60
80
100
ρ0 α TCR L (TMoy − T0 ) ∆R = S
Laser Power(mW)
MICROELECTRONICS
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Model Conclusion Localization of defects and lines submitted to Ileakage ∆R 1/∝ Section ∆V ∝ Ileakage Localization of junctions and interface defects Q12 or ∆T Precise localization Thermal diffusion < 30µm Tmax at center of line and laser beam MICROELECTRONICS
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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 :
MICROELECTRONICS
Techniques
Inventor
Bias
Amplifier
OBIRCH
Nikawa
V
I
CC-OBIRCH TIVA
Nikawa Cole
I
V
TBIP XIVA
Palaniappan Falk
V
V
SEI
Cole
I / None
V
TLS
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Configurations OBIRCH I.C. I.C.
AMPLI I/V
AMPLI V/V
TIVA I.C.
AMPLI V/V
MICROELECTRONICS
• Other configurations: – Inductance (TBIP / XIVA) – No bias (SEI)
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TLS on Test Structures Al line N+ resistance
Poly line No bias (SEI)
MICROELECTRONICS
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TLS Case Study #1 • Failed CMOS IC
TLS 200X
– I ~ 2mA @ 5V
• No emission • Front-side
TLS 5X MICROELECTRONICS
Metal short (M1-M2)
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TLS Case Study #2 • Failed BICMOS IC – I > 100 µA (I/O)
TLS (20x)
• Backside – 4 metal levels
EMMI (20x) MICROELECTRONICS
W short (Drain-Source)
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TLS Case Study #3 • Failed CMOS IC
TLS (20x)
– I ~ 2 mA @ 3V
• Front-side
Metal short TLS (20x) MICROELECTRONICS
(M2-M3)
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TLS Case Study #4 • ESD failed commercial ICs Molten Si spike
– HBM and MM stressed
• Front-side – No bias applied (SEI) SEI (200x)
SEI (50x)
Molten Si/Al filament MICROELECTRONICS
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TLS Case Study #5 • GaAs failed ASICS – I ~ 50 µA @ 3V
Defects induced by CDM type ESD stress
• Front-side
TLS (100x)
MICROELECTRONICS
Gold filament
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Conclusion : TLS Application Field Thermal Laser Stimulation Bias
No Bias
MICROELECTRONICS
Signature
Defect type
Material
Ileakage >1µA
Current lines Shorts ESD defects Voids
AI, W, Au, PolySi, Doped Si, Amorph. Si
ESD defects Interface defects
Metal / Metal Metal / Si Metal / Poly Si Melted Si / Si
All circuits Comparison
