IR-Based Temperature Measurement - Fraunhofer

Transcription

IR-Based Temperature Measurement in
Rotational Grinding of Sapphire Wafers
9th International Conference on
Advanced Manufacturing Systems and Technology
Mali Losinj, Croatia, June 16, 2011
Fritz Klocke, Olaf Dambon, Maurice Herben
Fraunhofer Institute for Production Technology, Aachen, Germany
Elso Kuljanic, Marco Sortino, Giovani Totis
Department of Electrical, Management and Mechanical
Engineering, University of Udine, Italy
© WZL/Fraunhofer IPT
Outline
1
Introduction
2
Temperature Measurement
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Conclusions and Outlook
Seite 1
Introduction
Sapphire and its Different Applications
Crystal properties
Lens/Case
LED
P-contact
p-GaN
AlGaN
InGaN MQW
N-contact
Mechanical – Chemical – Optical
n-GaN
GaN-Buffer
Substrate top side
Saphire substrate
Internal reflector
Cathode
Anode
Saphire Wafer
 Single crystalline with hexagonal-
c-plane
C-Axis
rhomboedral crystal lattice structure
 c-Plane Orientation (0001)
 defect und kontamination free
 Diameter 50 - 200 mm (2-8“)
 Tickness approx. 250 μm - 1 mm
r-plane
a-plane
Seite 2
Introduction
Process steps in Sapphire Wafer Manufacturing
Front-End-Field
Lapping
Polishing
nLo
ns
nLu
Thinning
Dicing
Epitaxy
Multi-Wire-Slicing
Back-End-Field
ns
Primary Requirements
Primary Requirements
 high form accuracy
 minimum wafer thickness
 low surface roughness
 low internal stress
 low sub-surface damage
 (low surface roughness and SSD)
Seite 3
Introduction
Rotational Grinding - Grinding Wheel and Process Kinematics
Feed Rate vf
Grinding Wheel
Wafer
Grinding Wheel Alignment
Segmented Grinding Wheel
Spindle Speed ns
Contact Zone
Wafer Speed nw
Seite 4
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 5
Principle Setup for Monitoring and Control in Rotational Grinding
Machine Tool Control
vf
Grinding Spindle
Cup Grinding Wheel
ns
Sapphire Wafer (IR Transparent)
Innovative IR Transparent
Vaccuum Chuck
nc
IR Radiation
Data Acquisition Chain
IR Sensor
Seite 6
Test Bench Setup for Silicon Grinding Developped by Pähler
tube shield
infrared camera
cable and tube
lead through
belt-drive
housing
bearing cage
thin section
bearing
pneumatic
cylinder
hollow shaft
Ingot
contact zone
pivot and
sliding unit
nc
drive motor
vf
ns
cooling
water supply
grinding wheel
machine base
cooling air supply
belt tensioning unit
Seite 7
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 8
Sensor Requirements
Optical Transmissivity of Sapphire and Wien’s Displacement Law
 Sapphire window
temperature
20 °C
200 °C
100
transmissivity [%]
90
80
400 °C
70
600 °C
60
800 °C
50
40
Wiens’s Displacement Law
 max · T = b
30
20
 Relation between spectral 10
intensity, wavelength and 0
temperature
 [μm]
2
3
4
5
6
7
8
Seite 9
Sensor Requirements
Selected IR-Camera
 Jenoptik VarioTherm
 Detector type: PtSi
 Detector wave length:
3,4 – 5 μm
 Detector resolution:
254 x 254 pixels
 Detector frequency: 50 Hz
 Accuracy < 100 mK
 Focus distance:
300 - 600 mm, depending
on object size
Seite 10
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 11
Experimental Setup
Test Bench Setup – Front View
Hembrug
Slantbed CNC
Hard Turning
Machine Tool
Grinding wheel
Machine
tool control
Test bench
IR-Camera
control
Test bench
control
Seite 12
Experimental Setup
Test Bench Setup – Back View
Test bench
IR-Camera
control
Hembrug
Slantbed CNC
Hard Turning
Machine Tool
Coolant flow
rate control
Air cooler
Coolant pump
Test bench
control
Coolant
Seite 13
Experimental Setup
Test Bench Setup – Front View
Existing part
of test bench
Extended part
of test bench
IR-Camera
Grinding Wheel
Coolant nozzle
Electric power
and air supply
Seite 14
Experimental Setup
Test Bench Setup – Camera Direction View
Chuck spindle
Sapphire
wafer
IR-Camera
Belt drive
Chuck motor
Seite 15
Experimental Setup
Test Bench Setup – Process Area
Grinding wheel
Sapphire
wafer
Wafer chuck
Coolant nozzle
Seite 16
Experimental Setup
Test Bench Setup – Process Allignment
Contact area
Sapphire
wafer
Wafer chuck
Grinding wheel
Seite 17
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 18
System Calibration
Calibration Setup – Influence of Abrasive Layer
Heater
Grinding wheel
Abrasive layer
Thermo couple
IR-Camera
Seite 19
System Calibration
Measurement Results – Influence of Abrasive Layer
120
110
100
grinding layer temperature (TC) [°C]
90
80
70
Muedia D46
Norton D9
Norton D46
60
Effgen D5
Atlantic D20
50
40
30
20
10
0
30
40
50
60
70
80
90
100
110
IR-Temperature [°C]
Seite 20
System Calibration
Calibration Setup – Influence of Wafer Thickness and Wafer Surface
1
2
Heater
3
1 Double side polished wafer, t = 500 μm
2 Double side polished wafer, t = 5 mm
3 Wafer, t = 500 μm, one side polished,
one side lapped (Ra  700 nm)
 Cold wafer (20° C)
 Heated and cooled down abrasive layer
Seite 21
System Calibration
Measurement Results – Influence of Wafer Thickness and Surface
120
110
100
grinding layer temperature (TC) [°C]
90
80
Muedia D46
70
thin polished wafer
60
thick polished wafer
lapped wafer
50
40
30
20
10
0
30
40
50
60
70
80
90
100
Seite 22
System Calibration
Calibration Setup – Influence of Wafer Temperature
1
2
Heater
 Heated and cooled down wafer
3
 Abrasive layer with constant temperature
(50 - 55°C)
1 Setup
2 Focus on heated wafer
3 Focus on abrasive layer
Seite 23
Analogy Tests on Test Bench
Calibration Setup – Influence of Wafer Temperature
70
60
50
40
polished wafer
lapped wafer
30
20
10
0
30
40
50
60
70
80
90
100
110
120
wafer temperature (TC) [°C]
Seite 24
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 25
Grinding Tests
Frame Content Depending on Grinding Kinematics and Detector Speed
spindle speed ns = 4000 1/min
detector frame rate = 50 Hz
grinding wheel position frame n
grinding wheel position frame n+1
wafer centre
ns
ns
20 ms
(50 Hz)
480°
segment
wafer
During recording of 1 frame, 72 segments pass 1 measurement spot
average “background” temperature
Seite 26
Grinding Tests
Grinding Test Results – Rough Segmented Porous D46 Wheel
Grinding conditions
 Metal bond D46 wheel
 ns = 3000 1/min
 nc = 50 1/min
wafer centre
 vf = 60 μm/min
 Brittle material removal
mechanism
 Good cooling conditions
Result
 Maximum detected
background temperature
~ 45 °C
Seite 27
Grinding Tests
Grinding Test Results – Fine Segmented D5 Wheel
Grinding conditions
 Metal bond D5 wheel
 ns = 3000 1/min
wafer centre
 nc = 50 1/min
 vf = 20 μm/min
 Ductile material removal
mechanism
 Bad cooling conditions
Result
 Maximum detected
background temperature
~ 130 °C
Seite 28
Outline
1
Introduction
2
3
Sensor Requirements
4
Experimental Setup
5
System Calibration
6
Grinding Tests
7
Seite 29
What Did We Learn and How Can the Results be Applied?
Conclusions
 The proof of concept for IR-based temperature measurement
in rotational grinding of sapphire wafers was successfully
achieved.
 Due to the limited detector frequency, the so called
“background temperature” of the abrasive layer is measured.
 Highest temperatures of about 130 °C were detected while
using a fine segmented wheel with small grit size and low
porosity.
Outlook
 Development of a sensor integrated vacuum chuck system
able to measure background temperatures on wafers down
to 20°C.
 Application of a faster IR sensor (> 6 kHz) for the detection of
peak temperatures which are expected to be much higher.
Seite 30
Thank you for your attention!
Questions?
The presented work was supported by the Seventh Framework Program
of the European Commission within the project entitled „ThermoGrind“
Seite 31

IR-Based Temperature Measurement - Fraunhofer

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