Photopolymers and Photoresists for Electronic

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Photopolymers and Photoresists for Electronic
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What is photopolymers
A polymer or plastic that undergoes a change in
physical or chemical properties when exposed to
light.
What is photoresists
photosensitive liquid polymer, used in
photolithography to produce integrated circuits.
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• Photopolymers are imaging compositions based on
  polymers/oligomers/monomers which can be
  selectively polymerized and/or crosslinked upon
  imagewise exposure by light radiation such as
  ultra-violet light. For final use, they are made
  into different forms including film/sheet,
  liquid, solution etc. which find outlets in
  printing plates, photoresists, stereolithography
  and imaging.

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• Photoresists are used to make integrated
  circuits, flat panel displays, printed circuits,
  chemically milled parts, etc.
• A photopolymer product can be applied as a very
  thin coating as in liquid photoresists or formed
  into a large model as in a stereolithographic
  equipment.

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• There are 2 types of photoresists
• Positive photoresist
• Negative photoresist
• Generally, positive resist give better resolution
  compare to negative resist, this is because ve
  resist swell during development process, hence
  affect the resolution.

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Positive Photoresist
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Methods for Positive Photoresist

• 1. Photomask is placed between UV source
• And the wafer
• 2. Region exposed to UV radiation become soluble
• Due to change in chemical structure, and when
  developed by developer solution, these regions
  are easily removed
• 3. Upon development, exposed areas are removed
• 4. Patterns form are same as those on mask

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Negative resist
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Methods for Negative Photoresist

• Pattern formed are the reversed of mask
• After exposure, the exposed area of negative
  resist absorbs the UV radiation and
  polymerization takes place
• This reaction caused crosslinking of polymer,
  making it insoluble to developer solution
• Upon development, only the unexposed area with no
  polymer linking reaction are washed away

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Resist Requirements

• Solubility- in organic solvent is necessary
• Adhesion- good adhesion properties to various
  substrate
• Etching resistance-
• Sensitivity and contrast- Sensitivity, related to
  ability of a polymer to undergo a structural
  modification on irradiation. Contrast, ability of
  a polymer to give vertical sidewalls. Resolution
  (the smallest line with which can be achieved)
  depends on the contrast.

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Resist Materials

• Conventional Photoresists
• Positive Photoresists
• - Consists of 2 components, Low molecular weight
  novolac polymer and the sensitiser
  (1,2-diazonaphthoquinone (DNQ))

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• Exposure of the resist to UV light results in
  photodecompositon of the sensitiser to an
  unstable ketocarbene
• This react with water to produce the base-soluble
  indene carboxylic acid
• Prevent dissolution of Novolac polymer in aqueous
  base

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Resist Materials

• Conventional Photoresists
• Negative Photoresists
• - UV sensitive groups (chalcone, cinnamate,
  styrylacrylate, etc) are included in the main
  chain/side chain of polymer.
• - UV irradiation gives rise to crosslinking

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Polymers for Electronics- Introduction

• Initially, electronics are dominated by
  traditional inorganic semiconductors, metals, and
  ceramics
• However in the last 20 years, the use of organic
  materials that can process electric charge has
  been developed

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Polymers for Electronics- Introduction

• Starting with polymer photoresist- esp. in
  circuit board
• Conductive polymers- Additions of metallic traces
  in the form of catalyst
• Examples of conductive polymers are
  polyacetylene- and polyphenylene- based compound
• Conductive polymers are used in light emitting
  diodes, conductive adhesives, biosensors, etc

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Conductive Polymers

• p-electron system shows features in electrical
  transport properties
• Examples of p-electron system interclated
  graphite, carbon-60, carbon nanotubes,
  charge-transfer complexes, etc