Electron Beam Lithography

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Electron Beam Lithography

• Bastien Ripoche
• Laurent Robin
• Javaria Ahmad
• Enric Herrero Abellanas

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• Patterning techniques
• The electron beam lithography
• Applications of the EBL
• Future oportunities for EBL

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Patterning Techniques

• Criteriums about different techniques
• Resolution
• Speed
• Easy fabrication
• Cost

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Patterning Techniques

• Optical Lithographya) Deep Ultarviolet
  Lithographyb) Extreme Ultraviolet Lithographyc)
  X Rays
• Nanoimprint

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1) Optical Lithography

• Photoresistive resine
• Patterns Masks
• Wavelenght resolution dependant

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Resolution Limits

• Contact

• Advantages
• Good resolution
• Drawbacks
• Masks thin and flexible
• Use -gtdefects

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Resolution Limits

• Proximity

• Advantages
• Masks lifetime high
• Drawbacks
• Resolution not as good
• Diffraction
• Fresnel diffraction

Gap 20-50 µm
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Resolution Limits

• Projection

• Advantages
• Good resolution
• No deterioration
• Image smaller than mask
• Drawbacks
• Fraunhoffer diffraction
• Compromise between resolution and depth of focus

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b) Extreme Ultraviolet Lithography

• Small wavelenght Better resolution
• No lences mirrors
• Laser plasma sources
• 10 nm

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c) X Ray

• lt 1nm for Medical purposes
• Problems of masks
• Lences, mirrors
• Difficult to produce

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2) Nanoimprint

• 2 techniques
• Heat resineCool down
• UV radiations

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Patterning Techniques

• EUV soon in fabrication
• NanoimprintE beamfor 22nm
• X Rays difficult

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The electron beam lithography

• Types of EBL
• Electron Beam Direct Write
• Electron Projection Lithography

Bragg-Fresnel lens for x-rays Paul Scherrer
Institute
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Electron Beam Direct Write

• An electron gun or electron source that supplies
  the electrons.
• An electron column that 'shapes' and focuses the
  electron beam.
• A mechanical stage that positions the wafer under
  the electron beam.
• A wafer handling system that automatically feeds
  wafers to the system and unloads them after
  processing.
• A computer system that controls the equipment.

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Electron Beam Direct Write

• Types of electron guns
• Thermoionic
• Field emission

• Write-field (WF)
• Scanning methods
• Raster scan
• Vector scan

Raith 150 Manual (Nanostructure Physics Dept.
KTH) Anders Liljeborg
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Specifications, a real example

• Raith150
• Beam size    2nm _at_ 20 keV
• Beam energy 100eV - 30 keV
• Minimum line width 20 nm
• Import file format GDSII, DXF, CIF, ASCII, BMP

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Electron Projection Lithography

• Electron Beam Direct Write

Limited throughput
Electron Projection Lithography
Huge penetration depth of electrons

• SCALPEL (Bell Laboratories and Lucent
  technologies) 1995
• PREVAIL (IBM) 1999

New solutions
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Electron Projection Lithography

• SCALPEL
• High contrast
• Image reduction

• PREVAIL
• Larger effective field

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Electron beam resists

1. Important parameters
2. Types of resist
3. Resist limitations

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EBL resists

• Important parameters
• Resolution (nm)
• Sensitivity (C/cm2)

• Types of resist
• Positive resist Polymethyl methacrylate (PMMA)
• Negative resist

Recent progress in electron-beam resists for
advanced mask-making by D.R.Medeiros, A.Aviram,
C.R.Guarnieri, W.S.Huang, R.Kwong, C.K.Magg,
A.P.Mahorowala, W.M.Moreau, K.E.Petrillo, and
M.Angelopoulos
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Resist limitations

• Tendency of the resist to swell in the developer
  solution.
• Electron scattering within the resist.
• Broadens the diameter of the incident electron
  beam.
• Gives the resist unintended extra doses of
  electron exposure .

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Applications of Electron Beam Lithography

• Research
• - Nanopatterning on Nanoparticles
• - Nanowires
• - Nanopillars
• - Gratings
• - Micro Ring Resonators
• - Nanofluidic Channels
• Industrial / Commercial
• - Exposure Masks for Optical Lithography
• - Writing features

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Nanopatterning on nanoparticles

• Significance
• - Photonic Crystals
• - Quantum Dots
• - Waveguides
• Electron Beam Lithography
• - Fine writing at moderate electron energies
• - 37nm thick lines with 90nm periodicity
• - 50nm diameter dots with 140nm periodicity
• (2003), Patterning of porous Silicon by Electron
  Beam Lithography, S. Borini, A. M. Rossi, L.
  Boarino, G. Amato

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Nanowires

• Applications
• - High-Density Electronics (Sensors, Gates in
  FETs)
• - Molecular Electronics Medical/Biological
  Applications
• EBL with Electrochemical size reduction
• - High-Resolution Controlled Fabrication
• - Widths approaching 10nm regime
• Patterning of Films of Gold Nanoclusters with
  Electron Beam Direct Write Lithography
• - Sub 50nm wide Nanowires
• - Controlled thickness at single particle level
• Controlled Fabrication of Silicon Nanowires by
  Electron beam lithography and Electro- chemical
  size reduction (2005), Robert Juhasz, Niklas
  Elfstrom and Jan Linnros
• Nanometer Scale Petterinng of Langmuir-Blodgett
  Films of Gold Nanoparticles by Electron Beam
  Lithography (2001), Martinus H.V Werts, Mathieu
  Lambert, Jean-Philippe Bourgoin and Mathias Brush

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Nanopillars

• Significance
• - Quantum Confinement Effects
• - Photoconductive response in Nanopillar arrays
• EBL and Reactive Ion Etching
• - Etched Pillars with 20nm diameter
• Nanotechnology using Electron Beam Lithography,
  Center for Quantum Devices

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Gratings

• Applications
• - Distributed Feedback Lasers
• - Vertical Cavity Surface Emitting Lasers
• Continuous Path Control Writing using EBL
• - Avoids stitching errors
• Nanotechnology using Electron Beam Lithography,
  Center for Quantum Devices

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Micro Ring Resonators

• Applciations
• - Optical Telecommunication and Networks
• EBL and Dry Etching
• - 105 devices/cm2 density

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Nanofluidic Channels

• Significance
• - Laboratory on a chip
• - Single Molecule Detection
• Electron Beam Lithography
• - Single step planar process
• - Tubes with inner dimension of 80nm

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Industrial Applications

• Exposure Masks for Optical Lithography using EBL
• Writing Features

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Some Applications of E-Beam Lithography

• Cryo-electric devices
• Optoelectronic devices
• Quantum structures
• Multi-gate Devices
• Transport mechanism for semi and superconductor
  interfaces
• Optical devices
• Magnetism
• Biological Applications
• Nano-MEMS
• Nanofluidics

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Future opportunities for electron beam lithography

1. Double gate FinFET devices
2. Single electron transistors
3. Photonic crystals

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Double gate FinFET devices - Concept

• Principle
• Full control over a very
• thin body region by two gates
• Fabrication thanks to e-beam
• - Beam diameter smaller than 2nm
• - Low energy (5 keV)
• - High resolution organic resist
• - Overlay accuracy thanks to scanning of
  registration marks
• - Silicon etching

20 nm electron beam lithography and reactive ion
etching for the fabrication of double gate FinFET
devices (2003), J. Kretz , L. Dreeskornfeld, J.
Hartwich, W. Rosner Nanoscale FinFETs for low
power applications (2004), W. Rösner, E.
Landgraf, J. Kretz, L. Dreeskornfeld, H. Schäfer,
M. Städele,T. Schulz, F. Hofmann, R.J. Luyken, M.
Specht, J. Hartwich, W. Pamler, L. Risch
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Double gate FinFET devices Characteristics
Applications

• High performance devices
• Transfer characteristic similar to
• those obtained with bulk transistors
• Appl SRAM because high density
• capability of driving a large bitline load
• Low power applications
• High on-current, very low off-current

Nanoscale FinFETs for low power applications
(2004), W. Rösner, E. Landgraf, J. Kretz, L.
Dreeskornfeld, H. Schäfer, M. Städele,T. Schulz,
F. Hofmann, R.J. Luyken, M. Specht, J. Hartwich,
W. Pamler, L. Risch
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Single electron transistor - Concept

• Physic principle
• Weak external force to bring an additional
• electron to a small conductor island
• gt Repulsing electric field
• SET concept
• - Down-scaling
• - Low power consumption
• Difficulties
• - Need of very small islands because
• the addition energy must overload the
• temperature effects
• - Polarization in case of impurities
• gt randomness background charge

Single-Electron Devices and Their Applications
(1999), Konstantin K. Likharev
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Single electron transistor - Fabrication

• Classic technique
• Smallest island needed
• gt Use of high resolution lithography technique
• gt E-beam lithography
• With silicon nanowires
• Lithography with e-beam, with specific beam
  current density and dose
• Results single electron charging effect
• Polysilicon grain islands
• Grain boundaries mini tunnel barriers

Fabrication of silicon nanowire structures based
on proximity effects of electron-beam lithography
(2003), S.F. Hua, W.C. Wengb, Y.M. Wanb
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Single electron transistor - Applications

• Supersensitive electrometry
• Very small change of gate voltage
• gt measurable variation of I
• Very useful for physical experiments
• Single electron spectroscopy
• Replacing MosFET?
• Random access memory
• - Bit stored in large conductive
• island (floating gate)
• - Need of a sense amplifier
• gt association with FET amplifier
• - Very impressive density 1011 bit/cm

NO !!!
Single-Electron Devices and Their Applications
(1999), Konstantin K. Likharev
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Photonic crystals - Concept

• Aim propagation of light in a controllable
  manner
• gt Optical chips with waveguides, cavities,
  mirrors, filters
• Example of very compact quantum
• optical integrated circuit
• Need of a dielectric or metallic lattice, with
  adjustable parameters geometry, dielectric
  constant

Three-dimensional photonic crystals operating at
optical wavelength region (2000), Susumu Noda
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2D photonic crystals

• Creation of the desired lattice
• - With e-beam lithography at low beam energy
  (5keV)
• - Negative resist. Ex SU8-2000, with high
  refractive index (1,69) and good mechanical
  stability
• Results
• A few mode are allowed to propagate, depending
  of the photonic crystal parameters

Two-dimensional photonic crystal waveguide
obtained by e-beam direct writing of SU8-2000
photoresist (2004), M. De Vittorio, M.T. Todaro,
T. Stomeo, R. Cingolani, D. Cojoc, E. Di Fabrizio
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3D photonic crystals

• Several methods to create the lattice
• - Wafer-fusion and alignment
• technique
• Ex Layers of III-V semiconductors (AlGaAs)
• - XRay and e-beam lithography
• Introduction of defect states, light emitting
  elements)
• By wafer-fusion, two-resist process

Three-dimensional photonic crystals operating at
optical wavelength region (2000), Susumu
Noda XRay and e-beam lithography of three
dimensional array structures for photonics
(2004), F. Romanato, E. Di Fabrizio,M. Galli
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• Conclusion

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Thank you for your attention