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

 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 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)

Experimental Setup of µ-LAM System

Design of Experiments Scratch No. Loading g (mN) Machining Condition Cutting speed (µm/sec) Laser Power (mW) 12.5 (25)w/ laser (25)w/o laser (70)w/o laser10 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 #2 NO LASER HEATING AFM IMAGE OF THE SCRATCH #1 W/ LASER HEATING

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

Results and Discussion Cont’d Scratch # Machining Condition Cutting speed (µm/sec) Average Groove Depth (nm) 1w/ laser190 2w/o laser154 3w/o laser195 AVERAGE GROOVE DEPTHS MEASURED WITH AFM

Relative Hardness ww: scratch width A d : pressure area F n : thrust force H: relative Hardness Diamond Tool Laser Beam Substrate

Relative Hardness Cont’d RELATIVE HARDNESS OF THE SCRATCHES CUTTING SPEED = 1 µm/sec Scratch Depth (nm) Width of scratch ( μm) Machining Condition Thrust Force (mN) Relative Hardness (GPa) w/laser w/o laser w/o laser7040

Force Analysis at Constant Load Scratch Depth (nm) Width of scratch ( μm) Machining Condition Thrust Force (mN) Cutting Force (mN) Relative Hardness (GPa) w/laser w/o laser

Force Analysis at Constant Depth of Cut Scratch Depth (nm) Width of scratch ( μm) Machining Condition Thrust Force (mN) Cutting Force (mN) Relative Hardness (GPa) w/laser w/o laser

Mechanical Energy and Heat

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.

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

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

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

 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. Diamond Tools In μ-LAM

Chardon Diamond Tool K&Y Diamond Tool WMU Diamond Tool

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

Hardness-Temperature, 6H-SiC