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

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

2. Motivation • 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)

3. Potential Applications Grinding Polishing Lapping Diamond Turning • Tool wear • Machining time Machining cost 60-90% Semiconductor wafers Optical lens Ceramic seals

4. Background • 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

5. Solution ? Micro-Laser Assisted Machining (µ-LAM)

6. High Pressure Phase Transformation (HPPT) • HPPT is one of the process mechanisms involved in ductile machining of semiconductors and ceramics IR LASER DIAMOND TOOL SiC

7. Micro-Laser Assisted Machining (µ-LAM) • uses a laser as a heating source to thermally soften nominally hard and brittle materials (such as ceramics and semiconductors) • addresses roadblocks in major market areas (such as precision machining of advanced materials and products) • represents a new advanced manufacturing technology with applications to the many industries, including • Automotive • Aerospace • Medical Devices • Semiconductors and Optics

8. Objective • 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.

9. Scratch 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.

10. Experimental Procedure • 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.

11. Diamond tip (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.

12. Experimental Setup of µ-LAM System

13. Design of Experiments specifications of the scratches

14. Results and Discussion  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 #2 NO LASER HEATING AFM IMAGE OF THE SCRATCH #1 W/ LASER HEATING

15. Results and Discussion Cont’d Wyko Optical interferometer profile of the scratch #3 without laser

16. Results and Discussion Cont’d AVERAGE GROOVE DEPTHS MEASURED WITH AFM

17. Relative Hardness Laser Beam Diamond Tool Substrate w w: scratch width Ad: pressure area Fn: thrust force H: relative Hardness

18. Relative Hardness Cont’d relative hardness of the scratches cutting speed = 1 µm/sec

19. Force Analysis at Constant Load

20. Force Analysis at Constant Depth of Cut

21. Mechanical Energy and Heat

22. Conclusion • 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. • The cutting force encountered with laser-heating is ~1/3 of the force seen without while the thrust force with laser-heating is ~1/2 of the force measured without.

23. Acknowledgement • Dr. Valery Bliznyuk and James Atkinson from PCI Department • Mr. Kamlesh Suthar from MAE Department • Support from NSF (CMMI-0757339) • Support from MUCI

24. THANK YOU Questions

25. Total Laser Power Calibration Laser output power measurements with and without the diamond tip attached. Total Power coming out of the tip : 43%

26. Laser Beam Profile 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)

27. µ-LAM System UMT Controller UMT Tribometer Laser Cable and BDO Laser Head Diamond Cutting Tool

28. Diamond Tools In μ-LAM • Four diamond tools were designed and purchased to be used with the above lasers. • A significant improvement to the laser delivery system was achieved with the addition of a laser head (from Laser Mechanisms), which provides precise x, y, and z positioning of the laser beam.

29. Diamond Tools In μ-LAM Chardon Diamond Tool K&Y Diamond Tool WMU Diamond Tool

30. Lasers In μ-LAM • three fiber coupled laser systems (400mW, 10W and 100W) were acquired and implemented for μ-LAM: • Furukawa (1480nm wavelength, max 400mW power) 10µm • VISOTEK (976nm wavelength, max 10W power) 100µm • IPG (1070nm wavelength, max 100W) 10µm 1480nm-400mW 1070nm-100W 976nm-10W

31. Hardness-Temperature, 6H-SiC