John A. Patten, Amir R. Shayan, H. Bogac Poyraz, Deepak Ravindra and Muralidhar Ghantasala Western Michigan University Kalamazoo, MI

 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) Motivation

Tool wear Tool wear Machining time Machining time Semiconductor wafers Optical lens Machining cost 60-90% Ceramic seals GrindingPolishingLapping Diamond Turning Potential Applications

 Semiconductors and ceramics are highly brittle and difficult to be machined by conventional machining Lapping, fine grinding and polishing Lapping, fine grinding and polishing High tool cost High tool cost Rapid tool wear Rapid tool wear Long machining time Long machining time Low production rate Low production rate Background

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

High Pressure Phase Transformation (HPPT ) SiC HPPT is one of the process mechanisms involved in ductile machining of semiconductors and ceramics

 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 Automotive Aerospace Aerospace Medical Devices Medical Devices Semiconductors and Optics Semiconductors and Optics Micro-Laser Assisted Machining (µ-LAM)

 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. Objective

 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. Scratch Tests

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 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 direction.

Diamond Tip Attachment Diamond tip (5  m radius) Ferrule (2.5mm diameter) (a)5 µm RADIUS DIAMOND TIP ATTACHED ON THE END OF THE FERRULE USING EPOXY (b)CLOSE UP ON DIAMOND TIP EMBEDDED IN THE SOLIDIFIED EPOXY. (b) (a)(a)(a)(a)

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

Laser Beam Profile 2-D 3-D Before attachment of the diamond tip After attachment of the diamond tip The laser driving current is 580mA (~75mW) The laser driving current is 214mA (~60mW) Out of focus On focus

Experimental Setup of µ-LAM System

Design of Experiments Scratch No. Loading g (mN) Machining Condition Cutting speed (µm/sec) Laser Power (mW) 1*2.5 (25)w/o laser305*0 2*2.5 (25)w/ laser305* (25)w/o laser (25)w/ laser1350 *Experiments performed previously by Dong and Patten (2005). SPECIFICATIONS OF THE SCRATCHES

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 #3 NO LASER HEATING AFM IMAGE OF THE SCRATCH #4 W/ LASER HEATING

Results and Discussion Cont’d Scratch # Machining Condition Cutting speed (µm/sec) Average Groove Depth (nm) Relative Hardness (GPa) 1*w/o laser305* *w/ laser305* w/o laser w/ laser19018 AVERAGE GROOVE DEPTHS MEASURED WITH AFM Thrust Force = 25 mN *Experiments performed previously by Dong and Patten (2005).

Results and Discussion Cont’d AVERAGE GROOVE DEPTH MEASURED WITH AFM IN (nm) WITH 2 DIFFERENT CUTTING SPEEDS, W/LASER AND W/O LASER

Mechanical Energy and Heat

µ-LAM System Laser Head UMT Tribometer Laser Cable and BDO Diamond Cutting Tool UMT Computer

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

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.  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  Dr. Valery Bliznyuk and James Atkinson from PCI Department  Kamlesh Suthar from MAE Department  Support from NSF (CMMI )  Support from MUCI

Hardness-Temperature, 6H-SiC

Hardness - Temperature RELATIVE HARDNESS OF THE 90 nm AND 95 nm DEEP SCRATCHES w/LASER AND w/o LASER CUTTING SPEED = 1 µm/sec Scratch Depth (nm) Machining Condition Thrust Force (mN) Relative Hardness (GPa) 90w/laser w/o laser7062