Ion Beam Lithography Focused Ion Beam Ion Projection

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

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

Motivation • SEMATECH and the ITRS • Beyond the 22 nm node Optical Lithography • High throughput • Resolution limited • EUV? Electron Beam Litho. • High Resolution • Serial process • Proximity Correction 3

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

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

[2] Ion – Solid Interactions 6

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 m 2 m 1 7

[6] 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 8

[4] 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. 9

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

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

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

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! 13

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

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

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

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

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

Ion Source: Elements • Ga+ ion beam • Tmelt = 29. 76 C • High source brightness • Large mass & energy spread • He+ ion beam • GFIS – 1 e. V of energy spread • Zeiss Orion Plus resolution <0. 25 nm • Between heavy ion and electron • Resist exposure 19

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

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 21

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

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. 23

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 24

Questions 25

References 1. 2. 3. 4. 5. 6. 7. https: //www. intechopen. com/books/advances-in-micro-nano-electromechanicalsystems-and-fabrication-technologies/nanolithography Wanzenboeck et al. Focused Ion Beam Lithography. Recent Advances in Nanofabrication. Techniques and Applications, 2011, In. Tech. Baglin, J. E. E. (2012). Ion beam nanoscale fabrication and lithography—A review. Applied Surface Science, 258(9), 4103 -4111. 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. 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. 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. 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 26