10. 14301500 LED Analysis Semicon Taiwan 2011

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


price 5x price 40x price

Costs for LED Light Source

Source: US Department of Energy


MOCVD EpitaxyBig Effect on Cost : Big Effect on Performance


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


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!



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.


Si and Mg Profiles


Average ConcentrationMeasure Peak Concentration

Layer Thickness

Long Term Precision for Si in GaN


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.




EAG Taiwan Can Provide:• Process Monitoring

Research & Development• Failure Analysis• Construction Analysis


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


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


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 undoped

InGaP Si: 4E18



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 undoped

InGaP Si: 4E18



• 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


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




22


Example: Commercial GaN LED Dislocation Density – XS & PV

1 2 3

2

3

1

PV

XS1 2 3

23

Rapid Typing of Dislocations


• 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.

24

Quantum Well and Superlattice

• Quantum well and superlattice layer thicknesses can be measured using high resolution TEM imaging.


2.71 nm1.11 nm

25




26

Quantum Well Composition


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.

27




28

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.


SEMEBIC

Defect

29

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.


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.




EAG Taiwan Can Provide:• Process Monitoring• Research & Development

Failure Analysis• Construction Analysis

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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.

33

Package and Wire Integrity


• Real Time X-ray (RTX) looks into the package providing images in real time.

• Examination of this LED reveals an open wire.

34

Curve trace results show a differencewhen compared with the good device:

Bad Good

Reverse Bias


Defect Detection by OBIRCH

• OBIRCH reveals a defect location.

• We can use the OBIRCH image to locate the defect for Dual Beam FIB.


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


Localized defect from OBIRCH

37


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


• Gas bubble that appear inside LED packaging can be extracted and analyzed by GC-MS.

39


EAG Service Offerings

EAG Taiwan Can Provide:• Process Monitoring• Research & Development• Failure Analysis

Construction Analysis (Reverse Engineering)

40

FTIR Identification of Polymer Materials

• Package material in this case identified as a modified epoxy.


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)

41

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.


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


n contact

p contact

W Rh

ITO GaN

W Rh

ITO GaNSiO2

Au

Au

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Quantum Well Composition


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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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

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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

10. 14301500 LED Analysis Semicon Taiwan 2011

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