Micro Laser Assisted Machining (µ-lam) of Semiconductors and Ceramics. Machining Direction

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1 Micro Laser Assisted Machining (µ-lam) of Semiconductors and Ceramics John Patten, Director, Manufacturing Research Center Western Michigan University Machining Direction IR laser Machining Direction Work piece material β-sn Si Lei Dong, University of North Carolina at Charlotte 1

2 Acknowledgments Western Michigan University - Manufacturing Research Center UNC Charlotte, Center for Precision Metrology NSF, DMR, Lynnette Madsen, Program Director High Pressure Phase Transformation Focused Research Group (NCSU, UT-Knoxville) 2

3 Motivation: Reduce the cost in precision machining of hard and brittle materials [Covalent semiconductor and ceramic materials] Grinding Polishing Lapping Machining cost 60-90% Tool wear Machining time Semiconduct or wafers Optical lens Ceramic seals 3

4 Outline of this presentation Introduction of HPPT(Si) Load Diamond tip Si β-sn Si Experimental design, results and analyses 15 scratch cycles 4 scratch cycles 2 scratch cycles Tool/Device Design Conclusions and future work Raman shift (cm -1 ) 4

5 Comparison of LAM and Micro LAM Laser-assisted machining of ceramic parts (Purdue News Service Photo) Scratching direction Diamond tool Load Metallic Phase 1480nm IR Laser (0-400mW adjustable) IR Beam 10μm Amorphous phase Reflection Refraction Absorption Scattering Machined Surface High power laser(kw) Directly heat surface material prior to machining Lower power laser (several watts) Selectively heat (under the tool) 5

6 High Pressure Phase Transformation Si-I (Diamond cubic) to Si-II (β-tin) at P trans =12 Gpa Diamond Anvil Cell (DAC) R (Ω) Si Indenter P (GPa) Dramatic electrical resistance drop Bridgman,1952; Jamieson, 1963(x-ray/DAC); Gridneva, 1972; Tabor,

7 Evidence of HPPT HPPT in silicon (Covalent to Metallic Transformation) 35 (Cube Corner) Crystalline Si Intensity (a.u.) Si III and Si XII Amorphous Si Raman shift (Rcm -1 ) Micro Raman of Si indentation (Huening, 2004) 0.5 µm Extruded material, SEM/TEM image of indents (Si), (Wen, 2004) 7

8 Ductile Regime Machining HPPT is the basis for ductile regime machining of brittle materials Ductile-to-Brittle Transition (DBT) Machining parameters: Tool geometry/depth of cut/feed rates,etc. Fracture free surface finish SEM Image of Si Curly Chips from ductile machining (Yan, 2003) Coarse Grinding Fine grinding Polishing SPDT Polishing SPDT=Single Point Diamond Turning 8

9 Scratching is a close analog of machining Pile-up Chip formation Slow speed (mm/sec) Diamond tip Fast speed (m/sec) Cutting Diamond tool tool β-sn Si Si Si β-sn Si Scratching Machining 9

10 Preferential heating is an essential concept of this device Heating source IR laser Work Piece Surface Diamond Tip/tool β-sn Si Softened material=>reduced hardness => Reduced tool wear 10

11 Previous work: IR detection of metallic phase of silicon IR laser beam 10μm Diamond Tip β-tin Si Covalent Si Photo detector 11

12 Current work: IR laser heating of metallic phase of silicon IR laser Evaluate preferential heating of the high pressure metallic phase of silicon β-sn Si Higher power laser 400mW 1480 nm wavelength 12

13 IR laser heating of metallic phase of silicon Laser power measurement (1480nm IR laser with 0~400mW adjustable power) 400 Beam profile Before diamond tip attachment After diamond tip attachment Laser driving current (ma) 63% power loss 13

14 IR laser heating of HP metallic phase of silicon AFM measurements of laser heated scratch 25 mn load 25 mn load Slower speed favors softening effect Longer Heating time favors softening effect 14

15 Estimated Hardness - Temperature From the groove geometry and load The estimated hardness is: 6 GPa (~ ½, or 50%) The estimated maximum temperature is: 600 C 15

16 In-situ IR thermal imaging of laser heating of high pressure metallic phase of silicon Stage moving direction Si Wafer IR camera lens Scratch groove size: 1~2 µm wide,~100 nm deep 16

17 In-situ IR thermal imaging of laser heating of high pressure metallic silicon 17

18 Calculated Estimates of Temperature Analytical Model (comparable to thermal images) Stationary Point Laser Source, 150 mw Moving Gaussian Laser Source, 150 mw 18

19 Stationary Laser point 2D plot of temp. Distribution, max temp. 778C at 10 sec 19

20 Temperature distribution with respect to depth at 10 sec max temp is 778 C 20

21 2D contour plot of temperature profile of Gaussian beam at 200 cm/s velocity 21

22 IR laser heating of metallic phase of silicon from thermal imaging experiments Raman spectra indicate heating/annealing mN load with laser running at 1270mA and 0.02 mm/sec scratching speed Edge Center 520 Si-I 353 Si-XII 436 Si-III 480 a-si mN load with laser running at 1270mA and a heating time of 20 seconds Edge Center 520 Si-I Raman shift (cm -1 ) Raman shift -1 (c) 22

23 Tool Design for µ-lam 23

24 Conclusion This project and device demonstrates the feasibility and capability to preferentially heat the HPPT material and ability to facilitate thermal softening of hard-brittle materials, rendering them soft and more pliable (ductile). IR laser β-sn Si 24

25 Publications of the research Dong, L., Paten, J. A., Miller, J. A., In-situ infrared detection and heating of metallic phase of silicon during scratching test, Int. J. manufacturing Technology, 7 [5/6] (2005) Dong, L., Paten, J. A., Miller, J. A., In-Situ Infrared (IR) Detection and Heating of the High Pressure Phase of Silicon during Scratching Test, Mater. Res. Soc. Symp. Proc. 841 (2005) Abdel-Aal, HA, Patten, JA, Dong, L, On the thermal aspects of ductile regime micro-scratching of single crystal silicon for NEMS/MEMS applications, WEAR, 259: Part 2 (2005) Dong, L., Paten, J. A., Miller, J. A., In-Situ Infrared (IR) Detection of the High Pressure Phase Transformation of Silicon during Scratching Test, ASPE Annual Meeting proceedings (2004). John A. Patten, L. Dong, Jimmie A. Miller, Electrical and Optical Detection of the High Pressure Metallic Phase of Silicon In-situ During Scratching with Diamond: Electrical and Optical Heating of the high pressure phase material and its effect on the material s hardness, ASPE 2003 Annual Meeting Proceedings Oct.26-31, Vol. 30, (2003)

26 Additional slides Contact Information: John Patten (269)

27 Hardness vs Temperature Plots 27

28 Tin (symbol: Sn) α-tin grey -crystal structure similar to Si and Ge Normal pressure above 13.2 C β-tin white----tetragonal structure (metallic) 28

29 High pressure phases of silicon Designation structure Pressure region(gpa) Si-I Cubic diamond 0~11 Si-II Si-III Si-V Si-VII Body-centered Tetragonal (β-sn) Body-centerd cubic Primitive hexagonal Hexagonal closepacked ~11-15 ~10-0 ~14-40 ~40 (Hu and Spain, 1986) 29

30 High pressure phases of silicon Hu and Spain,

31 Lens added to diamond tool Improve the diamond-laser tool design: Diamond radius and included angle Tool holder Optical fiber Diamond tool Focal lens Laser beam 31

32 Tool Design (2) 32

33 Scratch hardness calculation using P=F/A R 2 r D (Triflov, 1964) r : half the groove width; R: diamond tip nominal radius D: the groove depth Contact area: A= 0.5 (π r 2 ), where r=sqrt(d(2r-d)), F: load Contact pressure: P=F/A 33

34 Raman on annealing indents (Gogotsi, 2005) 34

35 Reflectivity of Si-II 1480 nm M. Hanfland, 1988 (Optical properties of metallic silicon) 35

36 Crystal data for high-pressure phases of silicon(hu, 2003) 36

37 ZEMAX simulation of ray tracing inside the diamond-laser system Detector 3 Detector 1 Laser beam Thin layer of UV-Epoxy Diamond tip Detector 4 Detector 2 37

38 Previous work: IR detection of high pressure metallic phase of silicon β-sn Si IR laser Different optical properties of covalent and metallic phase of silicon Optically detect the difference between the covalent and metallic phase in transmission 8mW low power laser 1310nm wavelength 38

39 (3)- IR detection of metallic phase of silicon -Experimental setup Laser fiber Load Photo detector Silicon wafer Gold coated Diamond tip 39

40 (3)- IR detection of high pressure metallic phase of silicon -Principle Diamond and Si are transparent to IR radiation; Metallic materials are not Gold coated Diamond tip IR laser beam 10μm Tip without gold coating SEM images Before Tip with gold coating After β-tin Si Covalent Si Background signal Photo detector 40

41 (3)- IR detection of metallic phase of silicon Detecting Procedures and results Load 20mN load Diamond tip Laser beam Scratching direction IR photo detector Silicon wafer Labview Program 41

42 (3)- IR detection of metallic phase of silicon -Results:20-50mN load An average of 11% voltage drop for 20-50mN load scratches 20mN Load 30mN Load AFM 40mN Load 50mN Load SEM 42

43 Thermal images of diamond tip Thermal images of the diamond tip at different power levels The front view 1270mA 1020mA 680mA 340mA IR Laser: 1.48 µm IR camera 2-6 µm At right angle Some overlap between the laser wavelength and the detector sensitivity range 43