scratch tests on 4h-sic using micro-laser assisted machining ( μ -lam) system
DESCRIPTION
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. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
Scratch Tests on 4H-SiC Using Micro-Laser Assisted Machining (μ-
LAM) System
Amir R. Shayan, H. Bogac Poyraz, Deepak Ravindra, Muralidhar Ghantasala and John A. Patten,
Western Michigan UniversityKalamazoo, 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 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
High tool cost
Rapid tool wear
Long machining time
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 LASERDIAMONDTOOL
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
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 <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(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)
Experimental Setup of µ-LAM System
Design of Experiments
ScratchNo.
Loadingg (mN)
Machining Condition
Cuttingspeed
(µm/sec)
Laser Power (mW)
1 2.5 (25) w/ laser 1 350
2 2.5 (25) w/o laser 1 0
3 7.0 (70) w/o laser 1 0
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
Cuttingspeed
(µm/sec)
Average Groove Depth
(nm)1 w/ laser 1 902 w/o laser 1 543 w/o laser 1 95
AVERAGE GROOVE DEPTHS MEASURED WITH AFM
Relative Hardness
2
22
wAd
d
n
AFH
w w: scratch widthAd: pressure areaFn: thrust forceH: relative Hardness
Diamond Tool
Laser Beam
Substrate
Relative Hardness Cont’d
RELATIVE HARDNESS OF THE SCRATCHESC U T T I N G S P E E D = 1 µ m / s e c
Scratch Depth(nm)
Width of scratch(μm)
Machining Condition
Thrust Force(mN)
Relative Hardness
(GPa)
90 1.9 w/laser 25 18
55 1.5 w/o laser 25 28
95 2.1 w/o laser 70 40
Force Analysis at Constant Load
Scratch Depth(nm)
Width of scratch
(μm)
Machining Condition
Thrust Force(mN)
Cutting Force(mN)
Relative Hardness
(GPa)
90 1.9 w/laser 25 8.0 18
55 1.5 w/o laser 25 7.5 28
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)
90 1.9 w/laser 25 8.0 18
95 2.1 w/o laser 70 27.3 40
Mechanical Energy and Heat
25 700 32000
5
10
15
20
25
30 27.3
8
000.16000000
0000001 0.9
Mechanical WorkHeat
Temperature (°C)
Ener
gy (n
W)
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-0757339)
Support from MUCI
Questions
THANK YOU
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 Profile2-D 2-D
3-D
Before attachment of the diamond tip After attachment of the diamond tipThe laser driving current is 580mA (~75mW)
The laser driving current is 214mA (~60mW)
Out of focus
On focusOn focus
µ-LAM System
Laser Head
UMT TribometerLaser 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
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
• VISOTEK (976nm wavelength, max 10W power) 100µm
• IPG (1070nm wavelength, max 100W) 10µm
1480nm-400mW976nm-10W
1070nm-100W
Lasers In μ-LAM
Hardness-Temperature, 6H-SiC
20 300 400 500 600 700 800 990 1100 1300 1500 15800
5
10
15
20
25
30
Hardness (GPa)
Temperature ( C)⁰
Hard
ness
(GPa
)