Ion Beam Lithography

1. Ion Beam Lithography:
Focused Ion Beam & Ion Projection
Lithography
Ziam Ghaznavi
CHE 384T Lithography
November 30th, 2017
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2. Outline/Agenda
• Motivation
• Ion – Solid Interactions
• Overview of IBL Systems
• Future Outlook
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3. Motivation
• SEMATECH and the ITRS
• Beyond the 22 nm node
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Optical Lithography Electron Beam Litho.
• High throughput
• Resolution limited
• EUV?
• High Resolution
• Serial process
• Proximity Correction
𝑅 = 𝑘
𝜆
𝑁𝐴
𝜆 =
ℎ
𝑃

4. Motivation
• Ion Beam Lithography!
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Focused Ion Beam (FIB) Ion Projection Lithography (IPL)
[2]

5. Motivation: Ions
• Small particle wavelength -Not diffraction limited
• Large Mass
• Less scatter – No proximity effects
• Delivery more energy than e-
• Additional capabilities:
5
[2]

6. Ion – Solid Interactions
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[2]

7. Elastic (Nuclear) Collisions
• Ion – Atom binary interactions
• Momentum or Kinetic Energy transfer
• Cause:
• Scattering: Low ion energy
• Target atom dislocation
• Ion implantation: Amorphization & atomic mixing
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m1 m2
m1
m2

8. Inelastic (Electronic) Collisions
• Conversion of KE to other forms of energy
• Required for ion induced chemical reaction
• Negligible scattering of incident ion
• Ionization of target atoms and SE generation
• SE play significant role in bond dissociation – resists
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[6]

9. Physical Milling or Sputtering
• Ability for resistless structuring
• Elastic Cascade Model
• Sputter or Milling Yield
• Target atom
• Ion species and energy
• Angle of incidence
• Orientation dependent
• Slow – high dose req.
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[4]

10. Gas Assisted Etching (GAE) and Deposition (GAD)
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[4]

11. GAE & GAD
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(Dr. Sirard, Lam Research)

12. GAE & GAD
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[2] [4]
Local
Nonlocal

13. Resists for IBL
• Secondary electron induced bond dissociation
• Energy deposition dependent resist
• Low mass to energy ratio – electric stopping
• High mass to energy ratio – nuclear stopping
• Positive tone resist becomes negative
• Crosslinking induced by radicals liberated by ions
• Pattern both pos./neg. by varying energy!
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14. Resists for IBL
• Larger mass restricts exposure depth
• Shot noise & LWR
• Poisson/Neyman distribution
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[5] [8]
𝜎 = 𝑁

15. History of IBL Development
• Mass spectrometry & ion implantation
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1970’s:
Emergence of
LMIS & GFIS
FIB tools
1980’s: FIB use
in
semiconductor
industry for
mask repair
and IC editing
1992:
Advanced
Lithography
Group (ALD)
formed to
produce IPL
tool
2000’s: IPL tool
unable to beat
OL and EBL
Now: Renewed
interest due to
22 nm node

16. Ion Beam Properties
• Energy spread leads to
chromatic aberration (blur)
• Space charge effects add to
energy spread
• Beam diameter
proportional to beam
energy
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Ga+
Ga+

17. Ion Sources: Plasma - Volume
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Electron Bombardment Ion
Source
Gas Discharge Ion Source

18. Ion Sources: Point Sources
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Gas Field Ionization Source
(GFIS)
Liquid Metal Ion Source
(LMIS)
[2]

19. Ion Source: Elements
• Ga+ ion beam
• Tmelt = 29.76 C
• High source brightness
• Large mass & energy spread
• He+ ion beam
• GFIS – 1 eV of energy spread
• Zeiss Orion Plus resolution <0.25 nm
• Between heavy ion and electron
• Resist exposure
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20. Ion Source: Elements
• Alloy Sources with E x B filters
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[5]

21. Ion Projection Lithography: Masks
• Thin metal membrane (Si) with apertures
• Control issues:
• Stress relief & thermal expansion
• Overlay or “Donut Problem”
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Feature A Mask B Mask

22. Future Outlook
• Multibeam tool: 43-APS by IMS
• Gas discharge broad beam
• Programmable shutter aperture plate
• 43,000 beams, demagnification 200x
• Ion dot matrix printing for NIL*
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[2]

23. Major Challenge
• Adoption in a large deeply established field
(semiconductor)
• Compatibility with other steps in fab process
• Requires a paradigm shift in industry
• Wet vs. Dry processes
• Device design etc.
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24. Summary
• Ion beam lithography is a versatile technique
• Key advantages:
• Not diffraction limit, no proximity issue, direct write
• Ion solid interactions play a key role in
understanding the technique
• New ion source elements, new capabilities
• Multibeam system development promising for
the NGL
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25. Questions
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26. References
1. https://www.intechopen.com/books/advances-in-micro-nano-electromechanical-
systems-and-fabrication-technologies/nanolithography
2. Wanzenboeck et al. Focused Ion Beam Lithography. Recent Advances in
NanofabricationTechniques and Applications, 2011, InTech.
3. Baglin, J. E. E. (2012). Ion beam nanoscale fabrication and lithography—A review.
Applied Surface Science, 258(9), 4103-4111.
4. Utke, I., Hoffmann, P., & Melngailis, J. (2008). Gas-assisted focused electron beam
and ion beam processing and fabrication. [review-article].
http://dx.doi.org.ezproxy.lib.utexas.edu/10.1116/1.2955728.
5. Bassim, N., nabil.bassim@nrl.navy.mil, Scott, K., Technology, N. I. o. S. a.,
keana.scott@nist.gov, Giannuzzi, L. A., et al. (2017). Recent advances in focused ion
beam technology and applications. MRS Bulletin, 39(4), 317-325.
6. Brun, S., Savu, V., Schintke, S., Guibert, E., Keppner, H., Brugger, J., et al. (2013).
Application of stencil masks for ion beam lithographic patterning. [Article]. Nuclear
Instruments & Methods in Physics Research Section B-Beam Interactions With
Materials and Atoms, 306, 292-295.
7. Rau, N., Stratton, F., Fields, C., Ogawa, T., Neureuther, A., Kubena, R., et al. (1998).
Shot-noise and edge roughness effects in resists patterned at 10 nm exposure.
[research-article]. http://dx.doi.org/10.1116/1.590407.
Disclaimer: Images do not belong to me
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