IR-Based Temperature Measurement - Fraunhofer-Institut f¼r

© WZL/Fraunhofer IPT

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 HerbenFraunhofer Institute for Production Technology, Aachen, Germany

Elso Kuljanic, Marco Sortino, Giovani TotisDepartment of Electrical, Management and MechanicalEngineering, University of Udine, Italy

Seite 1© WZL/Fraunhofer IPT

Outline

Introduction1

Temperature Measurement2

Sensor Requirements3

Experimental Setup4

System Calibration5

Grinding Tests6

Conclusions and Outlook7


IntroductionSapphire and its Different Applications

Crystal properties

Mechanical – Chemical – Optical

Saphire Wafer

Single crystalline with hexagonal-rhomboedral crystal lattice structure

c-Plane Orientation (0001)

defect und kontamination free

Diameter 50 - 200 mm (2-8“)

Tickness approx. 250 μm - 1 mm

P-contact

p-GaNAlGaN

InGaN MQW

n-GaNN-contact GaN-Buffer

Saphire substrate

Internal reflector

Lens/Case

Cathode Anode

LED

Substrate top side

C-Axisc-plane

r-plane a-plane


IntroductionProcess steps in Sapphire Wafer Manufacturing

Back-End-FieldFront-End-Field

nLo

nLu

ns

ns

Primary Requirements

minimum wafer thickness

low internal stress

(low surface roughness and SSD)

Primary Requirements

high form accuracy

low surface roughness

low sub-surface damage

Multi-Wire-Slicing Lapping Polishing Thinning Dicing

Epit

axy


IntroductionRotational Grinding - Grinding Wheel and Process Kinematics

Wafer

Grinding Wheel

Contact Zone

Segmented Grinding Wheel

Grinding Wheel Alignment

Feed Rate vf

Spindle Speed ns

Wafer Speed nw


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



Temperature MeasurementPrinciple Setup for Monitoring and Control in Rotational Grinding

Grinding Spindle

Cup Grinding Wheel

Innovative IR Transparent Vaccuum Chuck

Sapphire Wafer (IR Transparent)

IR Sensor

Data Acquisition ChainIR Radiation

nc

ns

vf

Machine Tool Control


Temperature MeasurementTest Bench Setup for Silicon Grinding Developped by Pähler

Ingot

housing

thin sectionbearing

grinding wheel

machine base

belt-drive

infrared camera cable and tubelead through

tube shield

pneumaticcylinder

drive motor

pivot andsliding unit

cooling water supply

belt tensioning unit

hollow shaft

bearing cage

cooling air supply

ns

nc

vf

contact zone


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



Sensor RequirementsOptical Transmissivity of Sapphire and Wien’s Displacement Law

Sapphire window temperature

Wiens’s Displacement Law

max · T = b

Relation between spectral intensity, wavelength and temperature

100 transmissivity [%]

90

80

70

60

50

40

30

20

10

02 3 4 5 6 7 8

[μm]

20 °C

200 °C

400 °C

600 °C

800 °C


Sensor RequirementsSelected 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


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



Experimental SetupTest Bench Setup – Front View

Grinding wheel

Machinetool control

Test benchcontrol

Test bench

HembrugSlantbed CNCHard TurningMachine Tool

IR-Cameracontrol


Experimental SetupTest Bench Setup – Back View

Coolant pump

HembrugSlantbed CNCHard TurningMachine Tool

Coolant flowrate control

Coolant

IR-Cameracontrol

Air cooler

Test benchcontrol

Test bench


Experimental SetupTest Bench Setup – Front View

Extended partof test bench

Coolant nozzleElectric powerand air supply

IR-Camera

Existing partof test bench

Grinding Wheel


Experimental SetupTest Bench Setup – Camera Direction View

Chuck motor

IR-CameraSapphirewafer

Chuck spindle

Belt drive


Experimental SetupTest Bench Setup – Process Area

Coolant nozzle

Grinding wheel

Wafer chuck

Sapphirewafer


Experimental SetupTest Bench Setup – Process Allignment

Grinding wheel

Wafer chuck

Sapphirewafer

Contact area


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



System CalibrationCalibration Setup – Influence of Abrasive Layer

Abrasive layer

IR-Camera

Heater

Grinding wheel

Thermo couple


System CalibrationMeasurement Results – Influence of Abrasive Layer

0

10

20

30

40

50

60

70

80

90

100

110

120

30 40 50 60 70 80 90 100 110

IR-Temperature [°C]

grin

ding

laye

r tem

pera

ture

(TC

) [°C

]

Muedia D46Norton D9Norton D46Effgen D5Atlantic D20


System CalibrationCalibration Setup – Influence of Wafer Thickness and Wafer Surface

Heater

1 Double side polished wafer, t = 500 μm2 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

1 2

3


System CalibrationMeasurement Results – Influence of Wafer Thickness and Surface

0

10

20

30

40

50

60

70

80

90

100

110

120

30 40 50 60 70 80 90 100

IR-Temperature [°C]

grin

ding

laye

r tem

pera

ture

(TC)

[°C

]

Muedia D46

thin polished wafer

thick polished wafer

lapped wafer


System CalibrationCalibration Setup – Influence of Wafer Temperature

Heater

Heated and cooled down wafer Abrasive layer with constant temperature

(50 - 55°C)

1 Setup2 Focus on heated wafer 3 Focus on abrasive layer

1 2

3


Analogy Tests on Test Bench Calibration Setup – Influence of Wafer Temperature

0

10

20

30

40

50

60

70

30 40 50 60 70 80 90 100 110 120

wafer temperature (TC) [°C]

IR-T

empe

ratu

re [°

C]

polished waferlapped wafer


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



Grinding Tests Frame Content Depending on Grinding Kinematics and Detector Speed

wafer centre

detector frame rate = 50 Hz spindle speed ns = 4000 1/min

grinding wheel position frame n grinding wheel position frame n+1

20 ms(50 Hz)

wafer

segment

480°

nsns

During recording of 1 frame, 72 segments pass 1 measurement spot average “background” temperature


Grinding Tests Grinding Test Results – Rough Segmented Porous D46 Wheel

Grinding conditions

Metal bond D46 wheel

ns = 3000 1/min

nc = 50 1/min

vf = 60 μm/min

Brittle material removal mechanism

Good cooling conditions

Result

Maximum detected background temperature ~ 45 °C

wafer centre


Grinding Tests Grinding Test Results – Fine Segmented D5 Wheel

Grinding conditions

Metal bond D5 wheel

ns = 3000 1/min

nc = 50 1/min

vf = 20 μm/min

Ductile material removal mechanism

Bad cooling conditions

Result

Maximum detected background temperature ~ 130 °C

wafer centre


Outline

Introduction1



Experimental Setup4

System Calibration5

Grinding Tests6



Conclusions and OutlookWhat 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 ofpeak temperatures which are expected to be much higher.


Thank you for your attention!

Questions?

The presented work was supported by the Seventh Framework Programof the European Commission within the project entitled „ThermoGrind“

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IR-Based Temperature Measurement - Fraunhofer-Institut f¼r