Specialists in Materials Characterization
LED Analysis at EAG
Tim Chang and Gary Mount
© Copyright 2011 Evans Analytical Group® 2
EAG Background in Semi and LED
• Established in 1978, Silicon Valley California• EAG Taiwan established in 2000• Now over 15 locations in 7 countries• 30+ analytical techniques• Over 150 instruments• Over 300 scientists and engineers• Career scientists, many with Ph.D.• Foundation in semiconductor industry• Very active in LED space
– Process monitoring and R&D analysis for 20 years.
MOCVD Reactor Capacity by Region
© Copyright 2011 Evans Analytical Group® 3Courtesy of Yole Development
Barriers to Adoption
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price 5x price 40x price
Costs for LED Light Source
Source: US Department of Energy
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MOCVD EpitaxyBig Effect on Cost : Big Effect on Performance
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Epitaxy – MOCVD: Higher yields and throughputs –
Improved material quality.
Epitaxy: Cluster tools –New Epi technologies.
Substrate Separation: Laser Lift Off, other
separation techniques.
Lithography: Dedicated tools, higher throughput.
Mirrors:Resonant Cavities.
Mirrors: Improve reflectivity – electrical properties.
Contacts & Electrodes: Transparent contacts /
Electrode materials and patterns.
Contacts &Electrodes:
p to n layer VIAS.
Surface Texture:Patterned substrates/
Roughening.
Surface Texture:Photonic and QuasiPhotonic Crystals.
Current Droop:Green Gap – LED
Structures.
LED Performance
Man
ufac
turin
g C
ost
Alternative Substrates: #2: Si
Large Diameter Substrates: 4”, 6”, 8”. Wafer Level Packaging:
Silicon TSC, Wafer level optics.
Phosphors: Conversion efficiency, Color rendering –
‘IP Free’ phosphors.
Phosphors: Quantum dots phosphors
Alternative Substrate: #1: GaN, AnO, Si, Engineered
substrates.
Thermal Management: New materials for packaging.
Encapsulation Materials and Optics: Ageing and
optical properties.
Testing and Binning: Wafer level – Higher
throughputs.
Die Singulation: Increased throughputs and yields.
Courtesy of Yole Development
MOCVD Reactors
• It’s somewhat of an art [operating an MOCVD reactor]. You can’t make decent stuff [LEDs] without epitaxial active layers. Every machine has its own identity. You need R&D."
7
Aldo Kamper, president and CEO of Osram Opto Semiconductor
Interview with Greentechsolar: March 7, 2011
© Copyright 2011 Evans Analytical Group®
Testing and Binning
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A lot of this variability is created at the epitaxy stage:Within Wafer – Wafer to Wafer – Run to Run – Reactor to Reactor
Each part is binned for 3 parameters•Color•Forward Voltage•Brightness
Example:8 color bins4 Vf bins3 flux bins
Color
ForwardVoltage
Flux
For a customer that wants warm white, highest brightness and mid-range Vf, only 5% of the bin space qualifies.
Courtesy of Yole Development
LED Evaluation
• Binning can only be done by testing LED performance for finished devices.
• Much of the LED performance is determined by the device microstructure as grown by MOCVD epitaxy.
“MOCVD is really the weak point in LED manufacturing. Good die yields after binning are about 35% industrywide. Manufacturers really need some feedback loop on actual dopant concentration homogeneity to fine tune their tools.”
(Source: Yole Development)
• SIMS is an excellent way to monitor epitaxy microstructure and it can be done before any devices are made!
© Copyright 2011 Evans Analytical Group® 9
© Copyright 2011 Evans Analytical Group® 10
EAG Services for LED
EAG Taiwan Can Provide:• Process Monitoring• Research & Development• Failure Analysis• Construction Analysis (Reverse Engineering)
Process Characterization and Monitoring
• Characterizing the performance of MOCVD reactors using SIMS is one of our most popular analysis.
• SIMS is a powerful process characterization tool. We use SIMS depth profiling to look at layer structure and thickness, n and p type doping levels in all layers, and contaminants in all layers.
• Customers can compare center and edge growth on a wafer, can compare wafer to wafer, compare wafers from the center and edge of the platen, compare lot to lot from the same reactor, and compare reactors.
• As wafers get larger these comparative measurements will only become more important.
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Si and Mg Profiles
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Average ConcentrationMeasure Peak Concentration
Layer Thickness
Long Term Precision for Si in GaN
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Value of SIMS for Process Monitoring
• We currently have 2 major LED manufacturers who use EAG SIMS for MOCVD process monitoring.
• EVERY COMPANY THAT HAS USED SIMS FOR MOCVD PROCESS MONITORING IN A SERIOUS WAY HAS CONTINUED TO DO SO…. a very strong endorsement of the value of the measurements.
© Copyright 2011 Evans Analytical Group® 14
© Copyright 2011 Evans Analytical Group® 15
EAG Services for LED
EAG Taiwan Can Provide:• Process Monitoring
Research & Development• Failure Analysis• Construction Analysis
© Copyright 2011 Evans Analytical Group® 16
Research & Development
SIMS:•Dopant and contaminant concentration and distributionTEM:•Layer thickness / uniformity > primarily QW region•Growth quality – defects – dislocations type and number•QW interface sharpnessSTEM:•Layer compositionEBIC:•Junction and junction defects
© Copyright 2011 Evans Analytical Group® 17
III-V Layer Structure
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 0.5 1 1.5 2 2.5 3
DEPTH (microns)
CO
NC
ENTR
ATI
ON
(ato
ms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
Cou
nts
per S
econ
d
Ga->
InP HBT The layer structure can be seen and
thickness measured
InGaP Si: 3E19InP Si: 3E19InP undopedInGaP C: 3E19InP undopedInGaP C: 3E19
InGaP undoped
InGaP Si: 4E18
InP substrate undoped
© Copyright 2011 Evans Analytical Group® 18
III-V Dopants
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 0.5 1 1.5 2 2.5 3
DEPTH (microns)
CO
NC
ENTR
ATI
ON
(ato
ms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
Cou
nts
per S
econ
d
Ga->CSi
InP HBT Dopant concentrations can be profiled and quantified in
multiple layers.
InGaP Si: 3E19InP Si: 3E19InP undopedInGaP C: 3E19InP undopedInGaP C: 3E19
InGaP undoped
InGaP Si: 4E18
InP substrate undoped
© Copyright 2011 Evans Analytical Group® 19
III-V Contaminants
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 0.5 1 1.5 2 2.5 3
DEPTH (microns)
CO
NC
ENTR
ATI
ON
(ato
ms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
Cou
nts
per S
econ
d
Ga->
HO
InP HBT Performance destroying contaminants can be
measured and quantified
InGaP Si: 3E19InP Si: 3E19InP undopedInGaP C: 3E19InP undopedInGaP C: 3E19
InGaP undoped
InGaP Si: 4E18
InP substrate undoped
© Copyright 2011 Evans Analytical Group® 20
• Powerful analysis tool–Depth profiling dopants and impurities in III-V
heterostructures–Surface, layer, substrate and interface–Stoichiometry in some cases
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
DEPTH (microns)
CO
NC
ENTR
ATI
ON
(ato
ms/
cc)
Mg
Al (a.u.)
Si
In (a.u.)
Depth (micron)
Con
cent
ratio
n (a
tom
s/cm
3 )
p-GaNp-GaN p-AlGaNp-AlGaN InGaN MQWsInGaN MQWs n-GaNn-GaN
SIMS for Structure and Doping
Quantum Well Dopant
© Copyright 2011 Evans Analytical Group® 21
0 50 100 150 2000
1.0E18
2.0E18
3.0E18
4.0E18
5.0E18
0
0.020
0.040
0.060
0.080
0.100
DEPTH (nm)
Si C
ON
CE
NTR
ATI
ON
(at/c
m3 )
Ga,
In A
tom
ic F
ract
ion
Si
In→
PCOR-SIMSSM
• High depth resolution SIMS can reveal the doping profile within the quantum well.
• Best quantification is achieved using ‘PCOR-SIMS’, a protocol that provides accurate quantification in all matrix layers.
Analysis with high depth resolution SIMS
© Copyright 2011 Evans Analytical Group®
Research & Development
SIMS:•Dopant and contaminant concentration and distributionTEM:•Layer thickness / uniformity > primarily QW region•Growth quality – defects – dislocations type and number•QW interface sharpnessSTEM:•Layer compositionEBIC:•Junction and junction defects
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© Copyright 2011 Evans Analytical Group®
Example: Commercial GaN LED Dislocation Density – XS & PV
1 2 3
2
3
1
PV
XS1 2 3
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Rapid Typing of Dislocations
© Copyright 2011 Evans Analytical Group®
• The character of dislocations can be quickly determined using STEM imaging.
• By utilizing specific sample tilts, threading dislocations can be identified as having screw, edge, or mixed character.
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Quantum Well and Superlattice
• Quantum well and superlattice layer thicknesses can be measured using high resolution TEM imaging.
© Copyright 2011 Evans Analytical Group®
2.71 nm1.11 nm
25
© Copyright 2011 Evans Analytical Group®
Research & Development
SIMS:•Dopant and contaminant concentration and distributionTEM:•Layer thickness / uniformity > primarily QW region•Growth quality – defects – dislocations type and number•QW interface sharpnessSTEM:•Layer compositionEBIC:•Junction and junction defects
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Quantum Well Composition
© Copyright 2011 Evans Analytical Group®
Epi-layer Structure
STEM/EDS (at%)Location Al In
1 - -2 9 -3 - 64 - 35 - 2
1
2
3
4
5 STEM/EDS can determine composition of the quantum well layers with 2-3nm spot size.
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© Copyright 2011 Evans Analytical Group®
Research & Development
SIMS:•Dopant and contaminant concentration and distributionTEM:•Layer thickness / uniformity > primarily QW region•Growth quality – defects – dislocations type and number•QW interface sharpnessSTEM:•Layer compositionEBIC:•Junction and junction defects
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Finding Defects using EBIC
• Electron Beam Induced Current (EBIC) imaging is compared with standard SEM imaging. An EBIC ‘bright spot’ reveals a defect that is not seen in standard SEM.
© Copyright 2011 Evans Analytical Group®
SEMEBIC
Defect
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Analysis of EBIC Discovered Defect
• A closer view of the defect site shows large and small bright spots in the EBIC image.
• A cross section was prepared using FIB at the red line.
• A TEM image of the defect cross-section is shown aligned on the same scale as the EBIC image.
• A pit defect is present under the small bright spot
• Magnifying the TEM cross-section image vertically reveals a disruption in the quantum well epi-layer growth.
• The EBIC image is brighter where the quantum well is closer to the ITO layer.
© Copyright 2011 Evans Analytical Group® 30
Locate Junction by EBIC
• Top and bottom contacts are required.
• A current is passed through the sample.
• An electron beam is rastered over the sample and where it touches the electrical junction, current is induced.
© Copyright 2011 Evans Analytical Group® 31
© Copyright 2011 Evans Analytical Group®
EAG Services for LED
EAG Taiwan Can Provide:• Process Monitoring• Research & Development
Failure Analysis• Construction Analysis
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© Copyright 2011 Evans Analytical Group®
Failure Analysis
Mainly chip but also some full package• RTX: delaminations / cracks / voids / line breaks• OBIRCH: defect localization• FIB : cross-section and find defect• STEM / Auger: FIB follow up for defect ID –
composition – metal migration > Auger works well in FIB crater.
• GC-MS: Gas bubbles inside package.
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Package and Wire Integrity
© Copyright 2011 Evans Analytical Group®
• Real Time X-ray (RTX) looks into the package providing images in real time.
• Examination of this LED reveals an open wire.
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Curve trace results show a differencewhen compared with the good device:
Bad Good
Reverse Bias
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Defect Detection by OBIRCH
• OBIRCH reveals a defect location.
• We can use the OBIRCH image to locate the defect for Dual Beam FIB.
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Defect Analysis by Dual Beam FIB
After localizing by OBIRCH thedefect is cross-sectioned by FIBand imaged with SEM.Examples:•Metal migration – FIB cross-sectionand investigation by Auger.•Voids – FIB cross-section andinvestigation by SEM.•Particles – surface or FIB cross-section and investigation depending on size and possible organic content•Cracks – FIB cross-section and investigation by SEM•Delaminations – FIB cross-section and investigation by SEM
© Copyright 2011 Evans Analytical Group®
Localized defect from OBIRCH
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© Copyright 2011 Evans Analytical Group®
Failure Analysis
Mainly chip but also some full package• RTX: delaminations / cracks / voids / line breaks• OBIRCH: defect localization• FIB : cross-section and find defect• STEM / Auger: FIB follow up for defect ID –
composition – metal migration > Auger works well in FIB crater.
• GC-MS: Gas bubbles inside package.
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LED Discoloration
© Copyright 2011 Evans Analytical Group®
• Gas bubble that appear inside LED packaging can be extracted and analyzed by GC-MS.
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© Copyright 2011 Evans Analytical Group®
EAG Service Offerings
EAG Taiwan Can Provide:• Process Monitoring• Research & Development• Failure Analysis
Construction Analysis (Reverse Engineering)
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FTIR Identification of Polymer Materials
• Package material in this case identified as a modified epoxy.
© Copyright 2011 Evans Analytical Group®
761
830
1041
1086
1129
1182
1235
1301
1382
1455
1509
1608
1736
2868
2950
3523
LED Encapsulant
60
65
70
75
80
85
90
95
100
%T
1000 1500 2000 2500 3000 3500 Wavenumbers (cm-1)
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Construction Analysis – Package LevelMeasurement of the materials, structure, composition and doping profiles that comprise an LED
Phosphors
heat-sink/support
phosphors
chip
reflector
wireStructureMaterials and layout of the package and support structures can be examined in cross-section using SEM imaging and EDS analysis.
Sapphire
Ag
Au
Cu
GaN
SiliconeSiO2
Gd doped YAG
Materials identification in and around the LED chip includes and evaluation of the phosphors. In this case STEM/EDS identified the phosphor as Gd doped YAG. Lattice imaging and d-space measurements confirm YAG identification.
© Copyright 2011 Evans Analytical Group® 42
Construction Analysis – Die Level
Contacts
SiO2
ITO
RhW
Au
0 50 100 150 200 250 300 3500
10
20
30
40
50
60
70
80
90
100
Sputter Time (min)
Ato
mic
Con
cent
ratio
n (%
)
N-contact
Auger depth profile
Ga
N
ITO
O
In
Sn
RhWAu
W
3500
10
20
30
40
50
60
70
80
90
100
Ato
mic
Con
cent
ratio
n (%
)
W
Au
W Rh
ITO
O
Si
Ga
NIn
Sn
P-contact
Auger depth profile
n and p contact evaluation by Auger depth profiling
TEM cross-section of p contact
© Copyright 2011 Evans Analytical Group®
n contact
p contact
W Rh
ITO GaN
W Rh
ITO GaNSiO2
Au
Au
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Quantum Well Composition
© Copyright 2011 Evans Analytical Group®
Epi-layer Structure
STEM/EDS (at%)Location Al In
1 - -2 9 -3 - 64 - 35 - 2
1
2
3
4
5 STEM/EDS can determine composition of the quantum well layers with 2-3nm spot size.
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© Copyright 2011 Evans Analytical Group®
Deprocessed
Polished
Crater
Construction Analysis – Die Level
• Decapped LED may need to be polished to remove leads.
• The LED may need to be etched to remove passivation prior to SIMS analysis.
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
0 200 400 600 800 1000
Depth (nm)
Con
cent
ratio
n (A
tom
s/cm
3 )
1E+17
1E+18
1E+19
1E+20
1E+21
INTE
NS
ITY
(arb
itrar
y un
its)
Mg
Al (intensity) Si
45
© Copyright 2011 Evans Analytical Group®
Summary
Why Use EAG Taiwan?
1. Experts in LED Analysis2. Special Instruments for LED3. Fast Turnaround Time4. All Types of LED Analysis
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Specialists in Materials Characterization
End