Measurement of LEDs at wafer level...High speed wafer level measurement of LEDs is supposed to...

Copyright 2012 ITRI 工業技術研究院

Presentation Date, 14pts

Measurement of LEDs at wafer level

Pei-Ting Chou, Tzung-Te Chen Industrial Technology Research Institute, Taiwan


Introduction Manufacturing steps of LEDs

Hardware architecture of LED wafer prober

Testing procedure of LED wafer – Integrating Sphere

– Huge Si Detector

– Optical Simulation of different test equipment

Measurement of electro-optical properties

Summary – Wafer level testing result

Outline


SSL products

LED Luminaires / Lamps

LED module/package LED wafer/chip

ANSI C78.377 IES LM-79-08

CIE TC2-71

CIE 127:2007 IES LM-82-12/LM-XX

CIE TC2-50/TC2-63

CIE TC2-64 ??

Introduction

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Why do we need a wafer level testing? In order to ensure the LED quality in an early stage of production, large

quantities of LED chips are measured in high speed during the wafer level bulk testing.

Wafer level testing is important to ensure the quality and give the direct comparison and good correlation with laboratory measurement results.

Introduction

High speed wafer level measurement: High speed wafer level measurement of LEDs is supposed to extend CIE

127 (Measurement of LEDs) for processed LED wafer or LED chips

4 inch wafer / 40 mil × 40 mil LED chip ~ 7000 LED chips per wafer

Wecon Inc.


LED chips on wafer

Chip bonding

Wire bonding Curing Silicone/Epoxy

encapsulates

LED Lamp Binning & Sorting For LED package manufacturers

Substrate Epitaxy Buffer layer

Epitaxy Active layers

LED Wafer/Chip Prober For LED chip manufacturers

Packaging

Wafer Process

Sapphire/SiC GaN/AlN InGaN Mesa/Contact

Grind Cutting

Wafer Probing

LED wafer

Wafer map file

Probing Chip on tape

Mapping Sorter

Chips map file

Binning

Main Manufacturing Steps of LED

Binning

Vf

Color

MOCVD

Source : Chroma ATE Inc. Wecon Inc. MPI Inc.

LED lamp


• DUT：device under test • Test head： Including the entrance optic of an optical test equipment

Integrating sphere or Si Detector Fiber Optical Meter

• Test station： Actually a position of the fixture in an automatic test handler

under the center of the tangent plane of Integrating sphere under the center of the plane of Si Detector

• Automatic test handler： A machine to handle DUTs

Chuck (X、Y、Z) Vacuum Pump

• Fixture： A mechanic part of the test station or handler

DUTs on the Chuck uses the Vacuum Pump • Contact pin： A flexible mounted thin needle to contact the LED lead

The contact pins were connected to the SMU (2-wire mode) • DUT image recognition and positioning： A machine to identify DUT and define DUT positions

CCD module SMU

(Source Measurement Unite)

DUT (LED Chips)

Fixture/Automatic test handler

Contact pin

Vacuum Pump

Test head (Integrating Sphere)

Fiber

Test station

Chuck (X、Y、Z)

Measurement Height

Aperture

Optical Meter

Automatic Test System for the LED Chips

SMU (Source Measurement Unite)

Fixture/Automatic test handler

Contact pin

Vacuum Pump

Test head (Huge Si Detector)

Fiber

Test station

Chuck (X、Y、Z)

Measurement Height

Optical Meter

Hardware architecture of LED Wafer Prober


Fixed DUT (Chuck by Vacuum Pump)

Move DUT to the Test station (Integrating Sphere、Si Detector)

Contact the DUT (Contact Pins)

Record the Reverse current (SMU single pulse)

Record the Forward Voltage (SMU single pulse)

Record the wavelength、 half-width、Radiant Flux

(Optical Meter with single pulse)

Testing procedure of LED wafer

Wafer alignment (Scanning by CCD Module)

Chuck

Huge Si detector

Source : Chroma ATE Inc. / MPI Inc. / Wecon Inc.


Testing procedure of LED wafer

Fixed DUT (Chuck by Vacuum Pump)

Move DUT to the Test station (Integrating Sphere、Si Detector)

Contact the DUT (Contact Pins)

Record the Reverse current (SMU short pulse)

Record the Forward Voltage (SMU short pulse)

Record the wavelength、 half-width、Radiant Flux

(Optical Meter with short pulse)

Wafer alignment (Scanning by CCD Module)

Short pulses measurements： – Provide high speed testing – Avoid current heating effect of the DUT – Measurement comparability between different labs – Electrical property testing time < 10ms (per pulse) – Optical property testing time < 100ms (per pulse) – Total testing time per chip depends on the number of testing items, mostly close to 300ms (including stage move time).

Single pulse mode：

Multi-pulse mode： Single chip test timing diagram

Die 1 2 3 IR Vf

Optical Stage Move

t0 t1 t2 t3

Vf measurement

Optical measurement

Current pulse

Single die test timing diagram


Stress Controller

I-V

Auto-electrical properties

measurement

Auto-optical properties

measurement

Objective lens

Eyepiece

White Light

CCD Probe-1 Probe-2

Auto- Wafer Imaging

Probes Setting

Optical Fiber

Integrating sphere

CCD array

Grating

Low-Cost Spectrometer

Load LED wafer

Testing procedure of LED wafer － Integrating Sphere

Fixed DUT

Move DUT to Test station

Contact the DUT

Start measurement

Wafer alignment


Shift

4 inch integrating sphere

1024X768

Wafer mapping - CCD Module

2 inch integrating sphere

Aperture~14mm Aperture~42mm

View Angle~90° View Angle~128°

Measurement Height~7mm

Measurement Height~10mm

Method of LED wafer/chip partial radiant flux measurement with an integrating sphere

Testing procedure of LED wafer － Integrating Sphere

Source : Chroma ATE Inc. / MPI Inc. / Wecon Inc.


Huge Si Detector

Optical Fiber

Method of LED wafer/chip Total radiant flux measurement with a Huge Photo Detector (Si)

Huge Si detector

1024X768

Wafer mapping - CCD Module

Testing procedure of LED Wafer－ Huge Si Detector

Source: Chroma ATE Inc. / Wecon Inc.


Prober Vendor 1 Vendor 2 Vendor 3 Chuck Size 160 x 160 mm 160 x 160 mm 6" ~ 8"MAX Wafer Size 4" MAX 6" MAX 4" MAX Blue Tape Size 8“ MAX 8“ MAX 8“ MAX X-Y Resolution 0.5 um 1μm 1μm X-Y Accuracy < 8 um <±10μm (Max. with CCD) X-Y Repeatability <3 um <3 um X-Y Speed 100 mm/sec 100 mm/sec Stage Z Travel 10mm 10mm Z Resolution < 1.25 um 1μm 1μm Z Accuracy < 8 um ±4μm Z Repeatability <3 um < 2um Θ Range ± 15∘ ± 10∘ ± 15∘ Θ Resolution <0.0018∘ 0.001∘ 0.009∘ Accuracy 0.002∘ Repeatability 0.005∘

• Auto wafer imaging (1024X768) • Automatically skip around the defective chips • Auto chip horizontal adjustment • Auto compensation for Z axis height

• Height adjustable probe platform • Four head / ink-jet probes can be installed

Tester Vendor 1 & 2 Vendor 3 Light collection method Integrating sphere (2” or 4”) & Fiber Huge Photo Detector & Fiber

Spectrometer ZEISS OEM (256 Pixel CCD) Ocean (2048 Pixel)

Current Range 5A (MAX) 0.8A (MAX)

IF Pulse Width 1ms ~1ms

Voltage Range 50V 1~7V/7~20V

λp 310~1130 nm 380~780 nm

Chuck

Hardware architecture of LED Wafer Prober

Huge Si detector

Source : Chroma ATE Inc. Wecon Inc. MPI Inc.


Si Detector + 5mm BK7

Reflectance (%) Absorbance by Si Detector

0 0.771535581

5 0.730337079

10 0.692883895

15 0.655430712

20 0.61423221

25 0.576779026

30 0.539325843

Integrating sphere Reflectance of

inner sphere (%) Net into the integrating

sphere light 98 0.404494382 95 0.516853933 90 0.599250936 85 0.640449438 80 0.666666667 75 0.68164794 70 0.692883895

Incident into Si Detector (%)

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40

Reflectance of Si Surface (%)

Net

ligh

t (%

)

Incident into Si

Detector (%)

0.38

0.43

0.48

0.53

0.58

0.63

0.68

65 70 75 80 85 90 95 100Reflectance of inner sphere (%)

Net

lig

ht (

%)

Testing procedure of LED wafer Optical Simulation of different test equipment


Parameter Symbol Unit Condition (High-Power LED)

Forward Voltage VF1 V If=10uA VF2 V If=350mA

Reverse current Ir uA Vr=-5V Dominant wavelength λd nm If=350mA Spectra half-width Δλ nm If=350mA Radiant Flux Po mW If=350mA

Measurement of Electro-optical characteristics

Source : MPI Inc.


VF at 60mA (V) Leakage Current at -5V (A)

Output Power at 60mA (mW)

-20 0 20 40 60

-80

-60

-40

-20

0

X Axis Title

Y Ax

is Ti

tle

0.010000.050000.10000.30000.50000.70001.0002.0002.000

-20 0 20 40 60

-80

-60

-40

-20

0

X Axis Title

Y Ax

is Ti

tle

430.0432.8435.5436.9438.3439.6441.0442.4443.8444.4445.1446.5449.3452.0

-20 0 20 40 60

-80

-60

-40

-20

0

X Axis Title

Y Ax

is Ti

tle

50.00100.0130.0140.0150.0160.0170.0200.0250.0280.0280.0

-20 0 20 40 60

-80

-60

-40

-20

0

X Axis Title

Y Ax

is Ti

tle

3.0003.1003.1253.1503.2003.2253.2503.2753.3003.3253.3503.4003.5003.6003.600

Peak Wavelength at 60mA (nm)

Measurement of Electro-optical characteristics


Summary The high speed LED wafer level testing provides accurate optical and electrical

characteristics measurements, which can give the direct comparison and good correlation with laboratory measurement results.

The hardware architecture of LED wafer prober includes the Integrating sphere or Si detector、fiber、optical meter、movable chuck (X、Y、Z)、vacuum pump、contact pins、SMU and CCD module.

For one LED chip testing procedure with the multi-pulse mode，the electrical property testing time is less than 10ms (per pulse)，the optical property testing time is less than 100ms (per pulse)，the total testing time depends on the number of testing items.

For optical simulation of different test equipment，the net light into the huge Si detector is slightly greater than that into the integrating sphere.

The Electro-optical characteristics measurement including the forward voltage、reverse current、dominant wavelength、spectra half-width、radiant Flux.


Acknowledgement

• Dr. I-Shih Tseng and Bernie Chang of Chroma ATE. Inc. provided useful information and comments.

Thank you for your attention!

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