Static Thermal Laser Stimulation FIRITI Abdellatif 26-27 January 2009 TM
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History TLS = OBIRCh + TIVA + SEI
OBIRCh
Optical Beam Induced Resistance Change – Nikawa et Inoue (1993)
TIVA
Thermally Induced Voltage Alteration – Cole et Al. (1998)
Defect localization in conductive materials of an IC
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Semiconductors basics: Laser-Material Interaction IR LASER λ = 1,3 μm
Heating of die material No photoelectric generation Conduction Band
Ephoton < Egap. Valence Band High optical absorption by next material: • Metallization (Al / W…) • Polysilicon • Active silicon highly doped
α Aluminium = 1,1x106 cm−1
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Principle of Thermal laser Stimulation General Principle Laser scanning ⇒ Thermal gradient Æ Local ΔR induced inside metallizations tracks ⇒ Modification of current consumption of the IC ⇒ Correlation between laser position and measured variations ΔI or ΔV ⇒ Defect localization (resistive/short circuit/leakage) Laser I Al
Heated
or
Al
ΔI = (Δ R/V) I2 ΔV
or
Si-sub.
Laser
ΔV ΔR×I
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OBIRCh / TIVA IR Laser beam 1.3 μm ⇒ Frontside & Backside analysis
Heating of metallic elements Resistivity variation
Δρ = ρoαTCR(ΔT) Current variation
ΔΙ = -(ΔR/R²) V
@ constant V
Voltage Variation ΔV = ΔR I
OBIRCh
@ constant I TIVA
Localization of discontinuity inside metallic material and abnormal current paths observation
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Heating of metallic materials
Electrical current density :
j ≅ σ[E + Q(− ∇T )]
J = Je + Jstimu ↑ T° → Current variation ∇ T° → Additional current generated by stimulation
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Heating of metallic materials Laser Defect
Metal track
x
T
x |ΔR| x |ΔI|/|ΔV|
ΔI / ΔV
A
G*ΔI / G* ΔV
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Heating of metallic material Æ Resistance variation
ΔR =
ρ0L S
(α TCR
− 2δ T )Δ T
ΔR = αTCR * ΔΤ R0 Aluminum αTCR = 4,29x10-3 °C-1 δT = 2,36x10-5
αTCR → Temperature coefficient of resistance δT → Linear Temperature expansion
Note: Dopped Silicon & PolySi αTCR is depending on doping type and value
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Temperature coefficient of resistivity Littérature value
M a té ria u A lu m in iu m C u ivre T u n g ste n Fer P la tin e M a n g a n è se M e rc u re A llia g e N i,F e ,C r C a rb o n e G e rm a n iu m S iliciu m V e rre
Experimengtal values
A lp h a T C R (°C -1 ) 0 ,0 0 3 9 0 ,0 0 6 8 0 ,0 0 4 5 0 ,0 0 6 5 1 0 ,0 0 3 9 2 7 0 ,0 0 0 0 0 2 0 ,0 0 0 9 0 ,0 0 0 4 -0 ,0 0 0 5 -0 ,0 4 8 -0 ,0 7 5
Metal layer
Matériaux
Alpha TCR (°C)
Al/Cu (1%)
0,0035
W
0,0015
TiTiN
-0.01357
Poly
-0.006
(4.1015cm-3)
Semi conductors
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Poly (N+)
0,00075
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Sign of resistance change Case of metals and alloys materials : αTCR > 0
;
ΔR ⇑ R
;
Δi
⇓
; BLACK
⇑
; WHITE
Case of semiconductors materials : αTCR < 0
;
ΔR ⇓ R
;
Δi
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Synthesis of mapping color
αTCR
ΔR/R
Métal
>0
Augmentation
Semiconducteur
T0 B
T0
Tc
T0
Material 1
∇T
Material 2 T0
B
A
A
Tc
T0
⊕ Θ
Mat erial1
Material 2
∇T
(
)(
)
(
FEM≡ V12 = Q1 − Q2 * T − T0 = Q12 T − T0
)
Q → Thermo-electrical power or Seebeck coefficient of the element Q12 → Relative Thermo-electrical power Freescale Semiconductor Confidential and Proprietary Information. Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2006.
Materials
Q12 (μV/oC)
Al / W
7,0
Al / n+ Poly
-121
Al / n+ Si
-105
(1020 cm-3)
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APPLICATIONS OF THERMAL LASER STIMULATION
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OBIRCh Analysis on constraint aluminum track (0,8µm) V= 19,7 mV (I = 1mA)
αTCR > 0
OBIRCh image
Superimposed image
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OBIRCh Analysis on Polysilicon line (0.8μm) V= 3V (I = 1mA)
αTCR < 0
(Weak doping)
OBIRCh Image
αTCR > 0
(High doping)
V= 940 mV (I = 1mA)
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TLS application on shorted device
Technology: 0.25µm – 6 metal layers
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Physical analysis: SEM observation
Conclusion: Root cause of failure on this product was a short LIL (W). NB: Defect found in front-end level has been detected and localized through 6 metal layers
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SUMMARY OF STATIC TLS TECHNIQUES Interaction between IR laser beam and the IC material will generate: - Optical to thermal transformation, - Heating of conductive materials Æ modification of IC current consumption
OBIRCh Δ i = −α
TCR
* ΔΤ * (
U ) R
ΔI = -(ΔR/R)*I
TIVA
SEI
Δ V = α TCR * ΔΤ * R0 * I
ΔV= (Q1-Q2)*∇T= Q1-2* ∇T
ΔV = ΔR*I
Resistivity change detection
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Thermocouple detection
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Conclusion Thermal Laser Stimulation allows : •
Localizing accurrately metallic shorts via fronstide and backside of IC,
•
No shift of defect position, Weak thermal expansion (~30μm).
Localizing non metallic defect
Polysilicon bridging or melted silicon, Bridging active area, Implants defects, .. Spiking defects, Interface defects of vias/contact.
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A. Firiti
16/05/03
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