1. Copyright 2009 by Raith GmbH Chinese Raith User Meeting Electron Beam Lithography: EBL Basics, EBL Equipment and Related Technologies Guido Piaszenski Raith GmbH, Germany EBL Applications

2. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 2 Single electron device, Université de Louvain SiO 2 Nanowires, Uni Alberta Photonic Crystal, Uni Eindhoven Nanoelectronics Photonics Basic Research Nanomechanics Single Electron Transport, LMU Munich Meta material, Uni Karlsruhe Optical Properties EBL CNT Customer Applications: Nanodevices

3. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 3 Outline  EBL basics & related technologies  Process & resist technology  Electron scattering and resist interaction  Proximity effect & charging  Typical instrumentation  EBL equipment  Electron optics  Components of EBL systems  EBL writing strategies  EBL system concepts  EBL applications

4. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 4 coating or stripping step remover lift-off etching metal remover pattern transfer substrate resist substrate spin coating exposure substrate developing wafer after x process steps Process technology

5. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 5 remover Lift-Off etching metal remover pattern transfer substrate resist substrate spin coating exposure substrate developing metal etching substrate EBID gas injection Process technology

6. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 6 exposure by secondary electrons (SE I and SE II ) Forward scattering events very often scattering under small angles small-angle hence inelastic generation of Secondary Electrons with a few eV kinetic Energy Backward scattering events occasionally scattering under large angles large angle hence mainly elastic high kinetic energy, range of the primary electrons Electron scattering incident beam resist substrate SE II BSE SE I

7. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 7 C C C C C C O O H H H H H HH H H H H H H H H H C C C C O O n C H H H H H H H H C C C H H CCC C C C CC C C C C C C C C C O O H H H H H H H O O O H H H H H H H O O H H H H H H H O H H H C H Fragmentation of PMMA

8. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 8 Monte Carlo simulation  1400 PMMA, 30 kV, exposed line: 300 nm, 520 µC/cm 2

9. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 9 Developing  1400 PMMA, 30 kV, 300 nm Struktur, 520 µC/cm 2  with MIBK:IPA = 1:3 5 s 10 s15 s20 s 25 s30 s35 s40 s45 s50 s55 s60 s

10. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 10 Clearing dose 520 µC/cm 2 Cross-Section after developing for 30 s 460 µC/cm 2 640 µC/cm 2

11. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 11 Process Window Dose Developing (Time, Temperature) Process window

12. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 12 Clearing dose: Rule of thumb 2. Dose depends on beam energy 1. Minor influence of resist thickness on dose incident beam SE II BSE SE I

13. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 13 uncorrected Proximity effect corrected high dose incident beam SE II BSE SE I Proximity effect depends on beam energy, substrate, pattern various strategies for proximity correction, e.g. dose variation 1µm low dose

14. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 14 Charging insulator resist e-e- e-e- Displacement and distortion of exposed structures!

15. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 15 Use of conducting layers insulator metal resist e-e- 1. resist/metal/substrate 2. metal/ resist/substrate insulator resist metal disadvantage: sputtering or evaporation system required for metal deposition 3. conductive polymer /resist/substrate: additional spin coating step, but no metal etching required insulator resist conductive polymer

16. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 16 Exposure Results Optical Images after exposure

17. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 17 Some resists Positive resists  PMMA  ZEP  UV5 more info at: www.microresist.de | www.allresist.de | www.microchem.com http://snf.stanford.edu/Process/Lithography/ebeamres.html Negative resists  AR-N 7520 or ma-N2403  HSQ  SU8  UVN30

18. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 18 Chemically amplified resists SU8 resist chemically amplified resist most applications: used with postexposure bake for high contrast substrate spin coating exposure substrate developing prebake postbake chemically amplified resist: postexposure bake

19. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 19  use for example PMMA 950K from Raith’s EBL starter kit Getting started As an EBL beginner …  avoid chemically amplified resist because they need a carefully controlled post exposure bake  avoid very sensitive resists  make first tests with positive resist, because several tests can be made on one sample

20. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 20 coating or stripping step remover lift-off etching metal remover pattern transfer substrate resist substrate spin coating exposure substrate developing wafer after x process steps Process technology

21. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 21 Lift-Off Tips & Tricks  obtain an undercut resist profile by  using a double layer resist  using low beam energy  overdeveloping  overexposure  use an aspect ratio of resist: metal as large as possible  if possible use evaporation, not sputtering

22. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 22 Resist Wafer apply postbake to improve resist stability during etching for organic resists avoid etching processes with oxygen Wafer Etching Tips & Tricks  obtain cross-sections without undercut or overcut by  using high beam energy  avoiding overexposure and overdeveloping

23. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 23 Raith support special knowledge, e.g. EBL resist database general knowledge & support substrate resist substrate spin coating exposure substrate developing remover lift-off etching metal remover pattern transfer Process technology

24. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 24 Cleaning Spin coating Film thickness measurement Instrumentation Film thickness measurement Cleaning Spin coating Exposure Developing Inspection wet bench (eye-) shower for accidents with acids storage for chemicals stove / hotplate refrigerator spin coater stove / hotplate Film Thickness Probe Raith EBL system wet bench storage for chemicals optical microscope sputtering machine Raith EBL system process step substrate spin coating exposure substrate developing Exposure DevelopingInspection Raith application lab: Typical instrumentation

25. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 25 Outline  EBL basics & related technologies  Process & resist technology  Electron scattering and resist interaction  Proximity effect & charging  Typical intrumentation  EBL equipment  Electron optics  Components of EBL systems  EBL writing strategies  EBL system concepts  EBL applications

26. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 26 History of EBL systems and electron optics Some Milestones in the History of Electron Optics 1897 Discovery of the electron by J.J. Thompson 1924 P. De Broglie: particle/wave dualism 1927 Hans Busch: Electron beams can be focused in an inhomogeneous magnetic field. 1931 Max Knoll and Ernst Ruska built the first TEM 1938 Scanning transmission electron microscope (M. von Ardenne) 1939 First commercial TEM by Siemens (Ruska, von Borries) … 1964 First commercial SEM by Cambridge Instruments 1960s First EBL Systems and EBL Resists

27. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 27 Courtesy:SPIE Handbook of Microlithography EBL related components Most simple EBL system: Upgraded SEM

28. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 28 Courtesy:SPIE Handbook of Microlithography EBL systems

29. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 29 advantages: resolution, beam current stability, filament lifetime Source: (Gersley, J. Appl. Phys. 65 (3), 914 (1989)) a)thermal emission, tungsten or LaB 6 b) field emission, cold or thermal Electron guns

30. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 30  DeBroglie wavelength at 1 kV: 0.0387 nm  current resolution limit of electron optics is in the range 1 – 2 nm Courtesy: SPIE Handbook of Microlithography Electron beam resolution

31. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 31 Resolution limit in EBL ~ 5nm lines exposed in HSQ resist, J. Yang, MIT, and J. Klingfus, Raith, unpublished 4.69 nm

32. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 32 Courtesy:SPIE Handbook of Microlithography EBL systems

33. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 33 electro-magneticelectro-static F = q · (E + v × B) fast deflection large deflection Note: Maximum deflection is in the range of 100 µm for high resolution and good placement accuracy! Beam deflection

34. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 34 Courtesy:SPIE Handbook of Microlithography EBL systems beam blanker deflection

35. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 35 How is the exposure executed? Serial exposure can be time consuming Need for accurate stage movement: Stitching

36. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 36 Applications: Stitching

37. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 37 Compact design No chamber modification required Variable working distance Integral closed loop position control Position control independant of all SEM settings Excellent stability Laserinterferometer controlled stage stitching capability

38. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 38 Gaussian Beam Vector Scan High resolution electron optics optimised for smallest spot diameters Writing strategies: Gaussian beam Gaussian Beam Raster Scan Complex electron optics with high speed deflector for 200 MHz – exposure while moving the stage

39. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 39 stage motion beam motion Writing strategies: Write-on-Fly

40. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 40 Shaped Beam Vector Scan Complex electron optics with shaping apertures require high current densities Writing strategies: Shaped beam

41. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 41 Outline  EBL basics & related technologies  Process & resist technology  Electron scattering and resist interaction  Proximity effect & charging  Typical intrumentation  EBL equipment  Electron optics  Components of EBL systems  EBL writing strategies  EBL system concepts  EBL applications

42. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 42  fabrication of photo masks and imprint templates  direct write applications in rapid prototyping and low volume production (confined to ultrahigh resolution layer)  nanodevices in R&D Serial Exposure: EBL Applications

43. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 43 mask writer R&D attachments R&D systems throughput, complexity, costs flexibility, versatility Serial Exposure: EBL Systems

44. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 44 Capabilities of EBL Systems mask writerR&D systemsattachments stitching R&D stitchingsingle field wafers & masks small samples high resolution mask making high resolution chip exposuresmall layouts direct write (mix & match) mix & match automatable jobsfull automation imaging metrology multi user nano engineering imaging wafers & masks Wafer exposure?Sample size?Pattern size?Lithography resolution?Process control?University environment?New technologies?Automation? fuzzy classification - “systems in between”

45. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 45 Summary  EBL basics & related technologies  Process & resist technology  Electron scattering and resist interaction  Proximity effect & charging  Typical intrumentation  EBL equipment  Electron optics  Components of EBL systems  EBL writing strategies  EBL system concepts  EBL applications

46. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 46 t-gate HEMT, Courtesy F. Robin, ETH Zürich Mix & Match exposure (Overlay)

47. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 47 Global Wafer Marker A): no registration after global alignment: highly accurate stage is a must! Local Writefield Marker B): Best overlay required or inaccurate stage: Apply local registration after global alignment Mix & Match with / without accurate stage

48. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 48 HEMT Structures 1.Step: large electrodes with 200 nm gap 2.Step: Overlay of 80 nm gate line automatic mark scan Mix & Match exposure: Example

49. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 49 Applications 2004 Collection from RAITH picture award (end of 2004)

50. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 50 Applications 2005 Collection from RAITH picture award (end of 2005)

51. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 51 Applications 2006

52. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 52 Applications 2007

53. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 53 Applications 2008

54. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 54 Applications – 3D lithography New Zealand, 3D pattern in negative resist (OM and AFM image) M. Konijn, University of Canterbury, Christchurch, New Zealand Christchurch

55. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 55 Colombo St 50 microns = 1/20 mm 50 nm = 1/20,000 mm nm-map, R. Blaikie, University of Canterbury, New Zealand Application – high resolution map

56. Copyright 2009 by Raith GmbH Chinese Raith User Meeting 56 Summary  EBL basics & related technologies  Process & resist technology  Electron scattering and resist interaction  Proximity effect & charging  Typical intrumentation  EBL equipment  Electron optics  Components of EBL systems  EBL writing strategies  EBL system concepts  EBL applications