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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
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
• 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
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
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
Copyright 2012 ITRI 工業技術研究院
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.
Copyright 2012 ITRI 工業技術研究院
Acknowledgement
• Dr. I-Shih Tseng and Bernie Chang of Chroma ATE. Inc. provided useful information and comments.
Thank you for your attention!