Material aspects in power technologies – from failure analysis to material testing M. Nelhiebel Kompetenzzentrum für Automobil und Industrieelektronik (KAI) Automotive Division / Quality Management, Infineon Technologies Villach, Austria
EUFANET Dresden, 17.10.2012
Motivation and purpose Growing segment of the power semiconductor market for automotive and industrial applications Area shrinks imply increasing transient peak junction temperatures (>400°C in the silicon!) Technology solutions target metallization-stack and interconnect Thus, technology development partially turns into mechanical material engineering … … and physical analysis, as an essential development support, must adapt accordingly
Nelhiebel, EUFANET 17.10.2012
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outline Power pulses and area shrinks of power semiconductor devices corresponding temperatures, and how to survive Failure vs degradation, destructive vs non-destructive analysis Defects in thick metallization layers ¬ Relevance and detectability
Material parameters of metals and dielectrics Microstructure of metal layers ¬ Grains, phases, contaminands
Measuring mechanical parameters ¬ Metals, dielectrics
New materials, new approaches decapsulation revisited
conclusion Nelhiebel, EUFANET 17.10.2012
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Example for active power pulses: Smart power switch operated into a fault condition for car applications Load (e.g. flash lights)
Fault ! ~4A
e.g. short circuit Cable resistances & inductances
~ 70 A
8.65 mm 4 mm
~80 mV ~0.3 W
high
low
high
low
t
t
Nelhiebel, EMPA 18.11.2011
~40 V ~1-3 kW ~10-100 µs
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Subsequent power-device shrinks in the last ~12 years – for same application
8.65 x 6.0 mm2 12.8 x 10.3 mm2
6.4 x 10.3 mm2 3.652x2.140mm2
3.902x3.402mm2
2x 30m 2x12.2 mm2
2x 20 m
3.904x3.145mm2
7.8 mm2
2x 25 m 13.3 mm2
1997 Nelhiebel, EMPA 18.11.2011
2003 Copyright © Infineon Technologies 2010. All rights reserved.
2010 Page 5
Realistic power pulse and corresponding temperatures of a smart power switch
surface of the sun: 63 W/mm2
… continuous!
Nelhiebel, EMPA 18.11.2011
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Little information by failure spot analysis of end-of-life tested samples Smart Power Technology, 3 metal layers (AlCu), Planar PowerMOS
metal 3
Smart Power Technology, 2 metal layers (AlCu), Trench PowerMOS
metal 2 metal 1 silicon conclusion: it was too hot…
Nelhiebel, EUFANET 17.10.2012
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Schematic of active cycling degradation Increasing peak-temperature by cumulated damage - systematic effect with intrinsic statistical scatter, driven by thermo-mechanical stress DMOS temperature > 550°C
T_limit leading to immediate destruction of the DMOS-device by thermal runaway in the product- and load-specific pulse Shape
insufficient robustness of technology
< 400°C
worst case T_peak specified lifetime
worst case T_peak 1st event
worst case T_ambient
+85°C
Specified lifetime Nelhiebel, EMPA 18.11.2011
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log stress (#pulses) Page 8
degradation phenomena due to power pulses
Cracks in Cu power metal
Severe plastic deformation (voiding) of AlCu power metal Al-based PowerMetal, 3M pulses
Nelhiebel, EUFANET 17.10.2012
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development: the power metal as heat buffer
Thick power metals reduce the peak temperature and enable area shrinks Nelhiebel, EUFANET 17.10.2012
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thick power metal for thermal management = relevance of metal cracks and voids Cracks in Cu power metal air gap
Blocked heat transfer to copper increasing Si temperature thermal runaway
+50 K in Si
Thick metals gain importance when shrinking power MOSFETs for automotive and industrial applications Voids and cracks in thick metal layer stacks (including dielectrics and interconnect) are the relevant degradation phenomena Non-destructive analysis methods for such defects are required! Nelhiebel, EUFANET 17.10.2012
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Non-destructive ways to find degradation induced metal voids and cracks? Example SAM intact power metal
Flip device, remove lead frame Scanning transducer – emitted wave melt-up
Reflected waves as a function of local power metal aspect
degraded power metal
Nelhiebel et al, ESREF 2011
defects in power metal Nelhiebel, EUFANET 17.10.2012
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Poschgan et al, ESREF 2012 Page 12
outline Power pulses and area shrinks of power semiconductor devices corresponding temperatures, and how to survive Failure vs degradation, destructive vs non-destructive analysis Defects in thick metallization layers ¬ Relevance and detectability
Material parameters of metals and dielectrics Microstructure of metal layers ¬ Grains, phases, contaminands
Measuring mechanical parameters ¬ Metals, dielectrics
New materials, new approaches decapsulation revisited
conclusion Nelhiebel, EUFANET 17.10.2012
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Effect of power cycles on copper grain microstructure (~100k pulses) initial
Poly-heater test structure Thinning from backside, Large area FIB cuts through thick Cu
stressed Nelhiebel, EUFANET 17.10.2012
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Passive temperature cycles of Al layers on silicon
(PhD thesis W. Heinz, KAI/Erich Schmid Institut Leoben, Prof. G. Dehm) 600nm polycrystalline Al 0 cycles
1.000 cycles
W. Heinz, R. Pippan, G. Dehm, Materials Science and Engineering A 527 (2010) 7757
600nm epitaxial Al 0 cycles
1.000 cycles
Film stress at 25°C
10.000 cycles
10.000 cycles
Benefit of epitaxial metal proven by SEM + EBSD
Nelhiebel, EUFANET 17.10.2012
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mechanical characterisation of copper
(PhD thesis M. Smolka, KAI/Erich Schmid Institut Leoben, Prof. G. Dehm) Presented @ EMRS 2011, Nice, France M. Smolka, C. Motz, T. Detzel, W. Robl, T. Griesser, A. Wimmer, er and G. Dehm (2012). Novel temperature dependent tensile test of freestanding copper thin film structures. Review of Scientific Instruments. 83 (6), 064702.
Temperature dependent yield stress of a thin copper layer measured by micro-tensile tests
RT 200°C 400°C
150 Stress (MPa)
Stress (MPa)
150
100
50
Ultimate tensile strength Yield stress
100
50
0
0 0
10
20
30
Strain (%) Nelhiebel, EMPA 18.11.2011
40
50
0
100
200
300
400
Temperature (°C) Copyright © Infineon Technologies 2010. All rights reserved.
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mechanical characterisation of copper
(PhD thesis M. Smolka, KAI/Erich Schmid Institut Leoben, Prof. G. Dehm) 50 µm
100 µm
Tensile direction
Nelhiebel, EMPA 18.11.2011
Force measurement
Heating 1 for samples + thermocouple
Heating 2 for gripper + thermocouple
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Micro tensile testing
grain with „bad“ orientation fail first
E. Schmid, W. Boas, Plasticity of crstals, with special reference to metals (1935)
Nelhiebel, EUFANET 17.10.2012
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mechanical characterisation of dielectrics
(PhD thesis K. Matoy, KAI/Erich Schmid Institut Leoben, Prof. G. Dehm)
K. Matoy, H. Schönherr, T. Detzel and G. Dehm (2010). Micron-sized fracture experiments on amorphous SiOx films and SiOx/SiNx multi-layers. Thin Solid Films. 518 (20), 5796-5801. K. Matoy, T. Detzel, M. Müller, C. Motz and G. Dehm (2010). Interface fracture properties of thin films studied by using the micro-cantilever fraction technique. Surface and Coatings Technology. 204 (6-7), 878-881.
Metal/dielectric adhesion measured by micro-cantilever tests Nelhiebel, EUFANET 17.10.2012
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metallization stacks for thermomechanical robustness = relevance of material parameters Cracks in Cu power metal air gap
crack and void initiation by thermomechanical stress as a function of material parameters of metals and dielectrics
+50 K in Si
Complex multilayer structures for power metallization and interconnect, exposed to violent thermal rises imply high thermomechanical stress Microstructure, „contaminands“ and (possibly) intermetallic phases define material parameters and thus robustness Material parameters may change under stress
methods for microstructure analysis and mechanical parameters are required Nelhiebel, EUFANET 17.10.2012 Copyright © Infineon Technologies 2010. All rights reserved.
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Semiconductor suitable methods for material parameter measurement? Example nanoindenter
Laser heating for Temperature up to 500°C
• Localized measurement of mechanical properties • Temperature dependent mechanical properties • Compression / Tension / Bending test possible • Adhesion Nelhiebel, EUFANET 17.10.2012
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outline Power pulses and area shrinks of power semiconductor devices corresponding temperatures, and how to survive Failure vs degradation, destructive vs non-destructive analysis Defects in thick metallization layers ¬ Relevance and detectability
Material parameters of metals and dielectrics Microstructure of metal layers ¬ Grains, phases, contaminands
Measuring mechanical parameters ¬ Metals, dielectrics
New materials, new approaches decapsulation revisited
conclusion Nelhiebel, EUFANET 17.10.2012
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Review: difficulties in decapsulation of copper-devices motivate „inverse“ SAM
Nelhiebel, EUFANET 17.10.2012
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Advanced decapsulation procedures for copper based power metal stacks (J. Maynollo, IFAT QM FA) Copper metallization & copper bonds Organic solvant vs acidic decapsulation
Anilin/ Indolin/ Aceton/Brij®35
Nelhiebel, EUFANET 17.10.2012
Optimierte Säuredekapsulierung
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conclusion Trend in automotive and industrial power semiconductors Power semiconductor devices get smaller and hotter Power metallization and interconnect stacks become thicker and more
complex, involving new materials
degradation modes are cracks and voids in the
metallization/interconnect stack, blocking the heat transfer
Mechanical robustness is achieved by material parameter engineering
Requirements to FA Degradation analysis instead of failure analysis Nondestructive methods for the characterisation of voids, cracks and
delaminations inside the metal/dielectric layers
Mechanical material parameters of metals and dielectrics must be
measured during development and production
new analysis methods for new materials Nelhiebel, EUFANET 17.10.2012
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Thank you for your attention
Nelhiebel, EUFANET 17.10.2012
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