Jan M. Yarrison-Rice Physics Dept. Miami University/University of Cincinnati

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Jan M. Yarrison-RicePhysics Dept.Miami
University/University of Cincinnati
A Novices View of E-Beam Lithography
w/ Sebastian Mackowski Scott Masturzo -- UC

• Raith 150 User Meeting
• Stanford University
• September 29 30, 2003

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Brief History of Raith 150 at University Of
Cincinnati

• NSF MRI Grant funded August 2002
• Instrument installed July 2003
• Initial training sessions July 7-11
• Small groups (2-3) begin design exposure July
  to present

2 micron squares exposed on silicon w/ 100 nm PMMA
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Research Interests

• Surface Enhanced Microscopies, e.g. SERS
• Pickup Coils for Magnetic Field Sensing
• Electrochemical Sensing
• Photonic Bandgap (PBG) Structures

Exposure Schedule for Dimers
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Lithographic Requirements

• 50 to 200 nm feature sizes
• Inter-feature spacing as small as
• 50 nm
• Pattern on ITO glass, silicon, or silicon
  nitride/dioxide

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Exposure and Processing
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E-beam Source

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Source Properties
source type brightness(A/cm2/sr) source size energy spread(eV) vacuum requirement(Torr)
tungsten thermionic 105 25 um 2-3 10-6
LaB6 106 10 um 2-3 10-8
thermal (Schottky) field emitter 108 20 nm 0.9 10-9
cold field emitter 109 5 nm 0.22 10-10
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Block Diagram of E-beam
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E-Beam Column
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Charging on Sample
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Exposure Matrices
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Proximity Effect
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Evidence of Proximity
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Methods around Proximity
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Other Methods
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Surface Enhanced Spectroscopy
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Surface Enhanced Microscopies

• Dimers sharp edged doublets
• Ag or Au - on glass for optical access
• Size determined by plasmon frequency of nonlinear
  system
• Challenges..
• Sharp corners
• Closely spaced nanoparticles

100 nm square dimers separated by 50 nm
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Pick-Up Coils

• Contact Pads (200 mm)
• Coil lines (300 - 400 nm)
• Challenges
• Sharp corners
• Proximity effect of multiple lines
• Overlap of write-fields

Pick-up coil from a Distance
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Pick-Up Coil Close Up
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Electro-Chemical Sensors

• Interdigitated Arrays
• Long 100 to 500 nm thick fingers w/ 50 nm
  separation
• Large contact Pads separated by mm
• Au or Ag on glass

Top 500 nm digits, Bottom 200 nm digits
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Interdigitated Array 1

• 200 nm digits
• Separation 200 nm
• 495 PMMA A12 on Silicon 100 nm thick
• Challenges -
• Strong proximity effect
• Write field overlap
• Very different sized structures combined

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Interdigitated Array 2

• 150 nm digits
• Separated by 400 nm
• ITO on Glass
• 495 PMMA A12 to 100 nm thick

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PBG Structures

• 2D arrays of etched pores
• Particular Structures of Interest include
• De-multiplexer
• Polarization Switching
• Microcavity for Sensing

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PBG Structure Requirements

• 2D Triangular arrays of 150 nm etched holes
• Pitch 250 nm
• Silicon nitride/silicon dioxide planar waveguide
  substrate
• Challenges -
• Large field patterning write field overlap
  registration
• Two-step etching process

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Lithography Challenge

• Best practices to make small,
• closely spaced features
• Design of structure
• Dosage choices
• Aperture choice
• Resist
• What we have tried to date
• Dosage schedules within feature for proximity
• Lines around area features to sharpen edges
• Dots and their use to sharpen corners

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Other Challenges..

• EVERYTHING else!!
• - from making contacts, to metallic coatings, to
  liftoff
• All advice is welcome!