John A. Patten, Amir R. Shayan, H. Bogac Poyraz, Deepak Ravindra and Muralidhar Ghantasala
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John A. Patten, Amir R. Shayan, H. Bogac Poyraz, Deepak Ravindra and Muralidhar Ghantasala Western Michigan University Kalamazoo, MI. Scratch Tests on 4H-SiC Using Micro-Laser Assisted Machining ( μ -LAM) System. Motivation.

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John A. Patten, Amir R. Shayan, H. Bogac Poyraz, Deepak Ravindra and Muralidhar Ghantasala

Western Michigan University

Kalamazoo, MI

Scratch Tests on 4H-SiC Using Micro-Laser Assisted Machining (μ-LAM) System


Motivation
Motivation Ravindra and Muralidhar Ghantasala

  • Increasing industrial demand in high quality, mirror-like and optically smooth surfaces

  • High machining cost and long machining time of semiconductors and ceramics

  • Reduce the cost in precision machining of hard and brittle materials (semiconductors and ceramics)


Potential applications
Potential Applications Ravindra and Muralidhar Ghantasala

Grinding

Polishing

Lapping

Diamond Turning

  • Tool wear

  • Machining time

Machining cost

60-90%

Semiconductor wafers

Optical lens

Ceramic seals


Background
Background Ravindra and Muralidhar Ghantasala

  • Semiconductors and ceramics are highly brittle and difficult to be machined by conventional machining

  • Lapping, fine grinding and polishing

  • High tool cost

  • Rapid tool wear

  • Long machining time

  • Low production rate


Solution
Solution ? Ravindra and Muralidhar Ghantasala

Micro-Laser Assisted Machining (µ-LAM)


High pressure phase transformation hppt
High Pressure Phase Transformation (HPPT Ravindra and Muralidhar Ghantasala)

HPPT is one of the process mechanisms involved in ductile machining of semiconductors and ceramics

SiC


Micro laser assisted machining lam
Micro-Laser Assisted Machining (µ-LAM) Ravindra and Muralidhar Ghantasala

  • addresses roadblocks in major market areas (such as precision machining of advanced materials and products)

  • uses a laser as a heating source to thermally soften nominally hard and brittle materials (such as ceramics and semiconductors)

  • represents a new advanced manufacturing technology with applications to the many industries, including

    • Automotive

    • Aerospace

    • Medical Devices

    • Semiconductors and Optics


Objective
Objective Ravindra and Muralidhar Ghantasala

  • The objective of the current study is to determine the effect of temperature and pressure in the micro-laser assisted machining of the single crystal 4H-SiC semiconductors using scratch tests.


Scratch t ests
Scratch Ravindra and Muralidhar Ghantasala Tests

  • The scratch tests examine the effect of temperature in thermal softening of the high pressure phases formed under the diamond tip, and also evaluate the difference with and without irradiation of the laser beam at a constant loading and cutting speed.

  • The laser heating effect is verified by atomic force and optical microscopy measurements of the laser heated scratch grooves.


Experimental procedure
Experimental Procedure Ravindra and Muralidhar Ghantasala

  • Laser Furukawa 1480nm 400mW IR fiber laser with a Gaussian profile and beam diameter of 10μm.

  • Tool 90 conical single crystal diamond tip with 5μm radius spherical end.

  • Workpiece single crystal 4H-SiC wafers provided by Cree Inc.

    NOTE: The primary flat is the {1010} plane with the flat face parallel to the <1120> direction. The primary flat is oriented such that the chord is parallel with a specified low index crystal plane. The cutting direction is along the <1010> direction.


Diamond tip attachment

Diamond tip Ravindra and Muralidhar Ghantasala

(5 m radius)

Ferrule

(2.5mm diameter)

Diamond Tip Attachment

(b)

(a)

  • 5 µm RADIUS DIAMOND TIPATTACHED ON THE END OF THEFERRULE USING EPOXY

  • CLOSE UP ON DIAMOND TIP EMBEDDED IN THE SOLIDIFIED EPOXY.


Total power calibration
Total Power Calibration Ravindra and Muralidhar Ghantasala

Laser output power measurements with and without the diamond tip attached.

Total Power coming out of the tip : 43%


Laser beam profile
Laser Beam Profile Ravindra and Muralidhar Ghantasala

2-D

2-D

On focus

On focus

3-D

Out of focus

Before attachment of the diamond tip

After attachment of the diamond tip

The laser driving current is 214mA (~60mW)

The laser driving current is 580mA (~75mW)


Experimental setup of lam system
Experimental Setup of µ-LAM System Ravindra and Muralidhar Ghantasala


Design of experiments
Design of Experiments Ravindra and Muralidhar Ghantasala

specifications of the scratches

*Experiments performed previously by Dong and Patten (2005).


Results and discussion
Results and Discussion Ravindra and Muralidhar Ghantasala

 AFM measurements have been used to measure the groove size and to study the laser heating effect of the scratches made on 4H-SiC.

AFM IMAGE OF THE SCRATCH #3

NO LASER HEATING

AFM IMAGE OF THE SCRATCH #4

W/ LASER HEATING


Results and discussion cont d
Results and Discussion Cont’d Ravindra and Muralidhar Ghantasala

AVERAGE GROOVE DEPTHS MEASURED WITH AFM

*Experiments performed previously by Dong and Patten (2005).

Thrust Force = 25 mN


Results and discussion cont d1
Results and Discussion Cont’d Ravindra and Muralidhar Ghantasala

AVERAGE GROOVE DEPTH MEASURED WITH AFM IN (nm) WITH 2 DIFFERENT CUTTING SPEEDS , W/LASER AND W/O LASER


Mechanical energy and heat
Mechanical Energy and Heat Ravindra and Muralidhar Ghantasala


Lam system
µ-LAM System Ravindra and Muralidhar Ghantasala

UMT Computer

UMT Tribometer

Laser Cable and BDO

Laser Head

Diamond Cutting Tool


Diamond tools in lam
Diamond Tools In Ravindra and Muralidhar Ghantasalaμ-LAM

Chardon Diamond Tool

K&Y Diamond Tool

WMU Diamond Tool


Conclusion
Conclusion Ravindra and Muralidhar Ghantasala

  • Laser heating was successfully demonstrated as evidenced by the significant increase in groove depth (from 54 nm to 90 nm), i.e., reduced relative hardness ~40%, indicative of enhanced thermal softening ~700°C.

  • AFM measurements of the laser-heat assisted scratch grooves show deeper and wider grooves compared to scratches made without the laser heating assisted methods; which indicates favorable thermal softening effects ~700°C.


Acknowledgement
Acknowledgement Ravindra and Muralidhar Ghantasala

  • Dr. Valery Bliznyuk and James Atkinson from PCI Department

  • Kamlesh Suthar from MAE Department

  • Support from NSF (CMMI-0757339)

  • Support from MUCI


THANK YOU Ravindra and Muralidhar Ghantasala

Questions


Hardness temperature 6h sic
Hardness-Temperature, 6H-SiC Ravindra and Muralidhar Ghantasala


Hardness temperature
Hardness - Temperature Ravindra and Muralidhar Ghantasala

relative hardness of the 90 nm and 95 nm deep scratches w/LASER and w/o LASER

cutting speed = 1 µm/sec


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