Transcript Photopolymers and Photoresists for Electronic

Photopolymers and
Photoresists for
Electronic
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 ultraviolet 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.
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.
Positive Photoresist
Methods for Positive Photoresist
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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
Negative resist
Methods for Negative Photoresist
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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
Resist Requirements
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Solubility- in organic solvent is necessary
Adhesion- good adhesion properties to various
substrate
Etching resistanceSensitivity 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.
Resist Materials
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Conventional Photoresists
Positive Photoresists
Consists of 2 components, Low molecular
weight novolac polymer and the sensitiser
(1,2-diazonaphthoquinone (DNQ))
Exposure of the resist to UV light results in
photodecompositon of the sensitiser to an
unstable ketocarbene
 This react with water to produce the basesoluble indene carboxylic acid
 Prevent dissolution of Novolac polymer in
aqueous base
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Resist Materials
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a)
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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
Polymers for ElectronicsIntroduction
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 ElectronicsIntroduction
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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
Conductive Polymers
π-electron system – shows features in
electrical transport properties
 Examples of π-electron system; interclated
graphite, carbon-60, carbon nanotubes,
charge-transfer complexes, etc
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