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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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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.
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.
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.
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.
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
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
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.
Resist Materials • 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 base-soluble indene carboxylic acid • Prevent dissolution of Novolac polymer in aqueous base
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
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
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
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