Quadratmetergrosse Mikrostrukturen per Laser Ein Kinderspiel ?

1. QuadratmetergrosseMikrostrukturen per LaserEin Kinderspiel ? Patrik Hoffmann Karl Böhlen Yury Kuzminykh, …

2. Outline • Ablation process - limitations • Excimer lasers • Examples • Installation in Thun D. Bäuerle; Laser Processing and Chemistry,3rdEdititon, Springer Berlin, 2000

3. Application of lasers in materials processing:Intensity-Time Diagram PLA/PLD – pulsedlaserablation/ deposition LA – laserannealing LC – lasercleaning LIS – laserinduced isotope separation/IR – laserphotochemistry MPA/MPI – multiphotonabsorptionionization LSDW/LSCW – lasersupporteddetonation/combustionwaves LCVD – laserinducedchemicalvapourdeposition LEC – laserinducedelectrochemicalplating/etching RED/OX – long pulse orcw CO2-laser inducedreduction/oxidation D. Bäuerle; Laser Processing and Chemistry, 3rd ed. Springer, Berlin, 2000

4. ns-Machining vs. fs-Machining ns fs

5. Molybdenum: through-hole Thickness of the molybdenum: 12.5µm 250 mJ/cm2, 40 pulses at 10 Hz 25 mJ/cm2, 2000 pulses at 40 Hz

6. Molybdenum: multiple through holes Entrance Exit F = 25 mJ/cm2 2000 pulses, 40 Hz Maskdiameter D = 215 µm

7. Interaction of Excimer light pulse with material UV light is absorbed Melting takes place Plasma appears and ablation products are ejected Excimer ArF, 193 nm, 1000 mJ/cm2, 20 ns, image projection

8. Interaction 193 nm Excimer light with materials Optical penetrationdepth: Thermal penetrationdepth: : optical absorption coefficient [cm-1] D: thermal diffusivity [cm2 /s] l: pulse duration

9. Ablation quality pulse duration

10. Example: Human Hair Marking „Cold“ ablation? Srinivasan, 1982, IBM Yorktown Heights; Cold ablation by UV photon bond scission

11. What is an Excimer laser? • Gas laser using a combination of a noble and a reactive gas • Under pressure and electrical stimulation a pseudo molecule called Excimer (= excited dimer) is created • By spontaneous or stimulated emission it dissociates back into two unbound atoms (laser with one energy level!)

12. Wavelength of Excimer Lasers • The wavelength of an excimer laser depends on the molecules used (can not be tuned) • emission is in the ultraviolet range Most important technologically areArF (193 nm) and KrF (248 nm)

13. Schematic Set-up pre-ionization heat exchangers electrodes gas circulation fan

14. Temporal and Spatial Profile of the Beam • ~20 nsis a characteristic pulse length of ArFandKrFlasers • determinedbytheexcimermoleculeproperties - can not beeasilytuned

15. Excimer laser technical specs Average power: 1 W – 1000 W Peak power: up to 50 MW Pulse frequency: 1 Hz – 6 kHz Pulse duration: 5ns – 200ns

16. Microelectronic production State-of-the-art microstepperwithlaserandlens Wavelength 193 nm

17. Research High Power Excimer Laser • The ELECTRA KrF laser at NRL (Naval Research Laboratory) • pulses of 250 to 700 J at repetition rates of 1-5 Hz • electron beam pumped History of excimerlasershasstartedat NRL around 1975 withemissionfromXeBr

18. Installations in EMPA, Thun

19. Exitech M8000 Micromachining System

20. Exitech PPM-601E Gen6 Tool Some highlights • 3 m2 exposure area • Ultra high precision: x/y axis < 40 nm resolution (laser interferometer based encoders) • Repeatability 3 um over full travel (+/- 1.5 ppm)

21. Mask projection system

22. Focus control - resolution and N.A. f sin θ = NA θ d NA ­ = d / 2f Diffraction Resolution Limit Depth of Field Resolution and Depth of Field Examples

23. Advanced mask imaging Projection ablation options for complex surface shapes Variable aperture mask Gray scale mask Scanned mask &/or workpiece

24. Intensity modulation of the imaged pattern 1mm 1µm holes • Depth information incorporated in half-tone mask • Transmission varied by changing hole size or density 8-level Diffractive Optical Element Material: Polycarbonate; Laser: KrF excimer 248nm; Optics: x5, 0.13NA;

25. DOE-halftone ablation

26. Mask imaging from sub-microns to millimetres feature 1 µm 10 µm 100 µm 1000 µm

27. Synchronized Image Scanning (SIS)

28. Feature quality: fit of target shape The average deviation from the best fit ROC is 147 nm with a ROC of 59.2 μm while the target is 60 μm.

29. Laser machining of ceramics Schematic of one part of Scanning Atom Probe Instrument (SAP) Time-of-flight mass spectrometer Electrode (Al2O3) Micro tip Material sample 248nm (KrF) 10 J/cm2

30. Ablation through the Mask HR 308 nmMask Material: Al2O3 - ceramics Laser 308 nm, 10 J/cm2, 2000 pulses

31. Microstructures in „green“ ceramics 1/50 of energy density needed to machine Potential for highly efficient micro structuring of ceramics Green zirconia powder pressed and laser ablated after sintering Courtesy of EPFL

32. Laser Center EmpaThun

33. KeinKinderspiel

34. Capability summary • Ablation • Feature sizes: 200 nm to a few mm • Feature height or depth z: <50 nm – 250 µm • Direct laser cutting of 3D features • Thin film patterning • DUV lithography • Large area processing (up to 2000 mm x 1500 mm)

35. Thank you

36. Submicron structures Sub exposure wavelength periodicity in polymers by polarized excimer laser radiation. Important parameters are: Polymer Wavelength Angle of incidence PET thin film on a silicium wafer. The film was irradiated with 1000 pulses of 193 nm at a fluence of 3mJ/cm2. M. Bolle and S. Lazare, Applied Surface Science (1993)

37. Submicron structures (cont) Phase mask setup for submicron structures Experimental set-up for the generation of sub-micron gratings by laser-ablation Principle of the proximity phase mask setup with water immersion K. Zimmer et al, Appl. Phys. A 74, 453–456 (2002) B. Borchers et all, Appl. Phys. 107, 2010

38. Submicron structures (cont) 30 um • Sub micronfeaturesthrough material stress release • Importantparametersare: • Stretch direction of polymer • Wavelength • Angle of incidence • Energydensity PET exposed at 193nm 75 mJ/cm2 PET exposed at 248 nm 400 mJ/cm2 120 mJ/cm2 Courtesy Epfl