1. Ion Beam Lithography: Focused Ion Beam & Ion Projection Lithography
Ziam Ghaznavi
CHE 384T Lithography
November 30th, 2017

2. Outline/Agenda Motivation Ion – Solid Interactions
Overview of IBL Systems
Future Outlook

3. Motivation SEMATECH and the ITRS 𝑅=𝑘 𝜆 𝑁𝐴 𝜆= ℎ 𝑃 Beyond the 22 nm node
Optical Lithography
Electron Beam Litho.
High throughput
Resolution limited
EUV?
High Resolution
Serial process
Proximity Correction
𝑅=𝑘 𝜆 𝑁𝐴
𝜆= ℎ 𝑃

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

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

6. Ion – Solid Interactions
[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 m2 m1 m2 m1

8. Inelastic (Electronic) Collisions
[6]
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

9. Physical Milling or Sputtering
[4]
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.

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

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

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

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!

14. Resists for IBL Larger mass restricts exposure depth Shot noise & LWR
[5] [8]
Larger mass restricts exposure depth
Shot noise & LWR
Poisson/Neyman distribution
𝜎= 𝑁

15. History of IBL Development
Mass spectrometry & ion implantation
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
Ga+
Ga+

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

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

19. Ion Source: Elements Ga+ ion beam He+ 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

20. Ion Source: Elements
[5]
Alloy Sources with E x B filters

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

22. Future Outlook Multibeam tool: 43-APS by IMS Gas discharge broad beam
[2]
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*

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.

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

25. Questions

26. Disclaimer: Images do not belong to me
References
systems-and-fabrication-technologies/nanolithography
Wanzenboeck et al. Focused Ion Beam Lithography. Recent Advances in NanofabricationTechniques and Applications, 2011, InTech.
Baglin, J. E. E. (2012). Ion beam nanoscale fabrication and lithography—A review. Applied Surface Science, 258(9),
Utke, I., Hoffmann, P., & Melngailis, J. (2008). Gas-assisted focused electron beam and ion beam processing and fabrication. [review-article].
Bassim, N., Scott, K., Technology, N. I. o. S. a., Giannuzzi, L. A., et al. (2017). Recent advances in focused ion beam technology and applications. MRS Bulletin, 39(4),
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,
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].
Disclaimer: Images do not belong to me