Jie%20Sun

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Advanced Photoresist Technology

• Jie Sun
• EE 518
• Instructor Dr. Jerzy Ruzyllo
• Apr. 4 2006

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• Presentation outline
• Introduction of Photoresists
• Roadmap of Photoresist Technology
• Photoresists Solution for Submicron
• lithography
• Summary

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Introduction of Photoresists

• Photoresists Type
• Positive exposed regions dissolve (best
  resolution)
• Negative Unexposed regions dissolve ( Swelling)
• Photoresists Structure
• Resin a binder that provides mechanical
  properties (adhesion, chemical resistance)
• Solvent used to dissolve the resin, allowing
  the resin to be applied in a liquid state
• Photoactive Compound (PAC) Act to inhibit or
  promote the dissolution of the
• resin in the developer. PAC inhibits
  dissolution in positive resists before light
• exposure. After exposure the PAC promotes
  dissolution of the resin.

George Tech, Photoresists and Non-optical
Lithography
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Photoresists Chemistry (1)

• Positive Photoresist
• Two-component DQN resists
• DQN, corresponding to the photo-active
  compound, diazoquinone (DQ) and resin,
• novolac (N)
• Dominant for G-line (436nm) and I- line (365nm)
  exposure and not suitable for very
• short wavelength exposures
• Novolac (N) a polymer whose monomer is an
  aromatic ring with two methyl groups
• and an OH group.
• dissolves in an aqueous solution easily
• Diazoquinone(DQ)
• 20-50 weight
• Photosensitive
• DQ

UV
Carboxylic acid ( dissolution enhancer)
Stephen A. Campbell, The Science and
Engineering of Microelectronic Fabrication.
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Photoresists Chemistry (2)
Positive Photoresist

• DQ molecule will not dissolve in a base developer
  solution (pH gt7).
• UV light breaks the nitrogen molecule off forming
  an unstable molecule
• To stabilize itself, one of the 6 carbon atoms
  in the ring pops out of the ring (leaving 5)
• Once exposed to water (a developer /water
  mixture), an OH group attaches to the carbon
  atom, forming an acid.
• The acid can then react and dissolve with the
  basic developer solution.

• Advantage
• Unexposed areas unchanged by the presence of the
  developer, line width and shape of a
• pattern precisely retained.
• Novolac fairly resistant chemical attack, a good
  mask for the subsequent plasma etching

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Performance of Photoresists

• Resolution (um) - linearity/ minimum
• Sensitivity (mJ/cm2)
• Focus margin (um)
• Exposure margin ()
• Dry etch resistance(X)
• Heat resistance
• Adhesion
• Standing wave effect (and bulk effect)(um)
• BARC (bottom anti-reflective coating)
  compatibility
• Process margin/stability
• Shelf-life

Photoresists Profile
Han Ku Cho, Samsung Electronics Co., Ltd,
Lithography technology review of what it is and
what to be, March 2003
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Roadmap of Photoresists Technology
Han Ku Cho, Samsung Electronics Co., Ltd,
Lithography technology review of what it is and
what to be, March 2003
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Deep UV Photoresist

• Limitation of Novolac based Photoresist
• Strongly absorb below 250nm, KrF (248nm)
  marginally acceptable but not ArF (193nm)
• Photoresist Solution for Submicron Features
• PMMA
• PAGs ( Photoacid generator) replace PAC
• Contrast enhancement layers (CELs)
• Inorganic resist (Ag-doped Ge-Se)
• Silicon-containing resists (dry developable)
• Multi-layer photoresist

 
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PMMA (Ploymethyl methacrylate)

• Short-wavelength lithography deep UV, extreme
  UV, electron-beam lithography
• Resin itself is photosensitive
• Advantage high resolution
• Disadvantage
• Plasma etch tolerance is very low and thick PMMA
  to protect the thin film

• Dissociation changes chemistry of the plasma
  etch and polymeric deposits on the
• surface of the substrate.
• Low sensitivity Add PAG (chemically reactive
  dissociating) or elevate exposure
• temperature

 
Stephen A. Campbell, The Science and
Engineering of Microelectronic Fabrication.
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Contrast enhance layers (CELs)

• CEM photo-bleachable
• Spun onto the DQN PR after softbake
• Formed in-situ conformal contact mask
• Enhanced contrast
• Important for DUV resists with less optical
  intense and PR radiation absorbtion

 
http//www.microsi.com/photolithography/data_sh
eets/CEM20365iS20Data20Sheet
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Inorganic Resist

• Advantage
• High contrast ? 7
• Produce fine line
• Process Ag-doped Ge-Se
• Ag plated on sputtered Ge-Se
• Photodoping create Ag2Se after exposure
• Dissolved in alkaline solution
• Disadvantage
• Require thick planarizing underlayer due to
• thin film nature
• Pineholes and defects from Ge-Se

 
Stephen A. Campbell, The Science and
Engineering of Microelectronic Fabrication.
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Dry developable Polysilynes

• Bi-layer process
• Silicon-containing resists on top of novolac
  based resist
• Highly resistant to plasma process
• Bleaching under DUV exposure due to cross-linked
  siloxane network
• Etch silicon selectively to silicon dioxide in
  HBr plasma

Roderick R. Kunz, et al, 193 nm Resists and
Lithography, Polymers for Advanced Technologies,
Volume 5, p p.12-21
 
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Multi-layer Resists and Hard mask

• Tri-layer process
• Thin layer PR SiO2
• thicker planarizing
• Oxide layer act as hard mask
• Oxide layer Dry etching
• resistant layer

E.Ong and E.L.Hu, Multilayer Resists for Fine
Line Optical Lithography, Solid State Technol.
 
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Process Comparison for SLR, BLR and MLR
Han Ku Cho, Samsung Electronics Co., Ltd,
Lithography technology review of what it is and
what to be, March 2003
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Summary

• Photoresists technology Basic and key
  technology in lithography
• PR chemistry structure changed with wavelength
  of light source
• Several PR solutions for DUV application
• Multi-layer PR replace the single layer for
  Sub-100nm features