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Photolithography tutorial

Modules

1. Optical sources
2. Photoresists

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  • Lithography type - there are two types of photoresist (i.e. 2 types of lithography)
    • Positive - the photoresist will dissolve after being exposed to light
    • Negative - the photoresist will not dissolve in the regions where it was exposed to light, but will dissolve in the regions where there was no exposure

  •  Photoresist composition
    • Solvent: gives the resist its flow characteristics
    • Resin (matrix material): polymers used as binder; gives the mechanical and chemical properties of the resist
    • Sensitizers: (PAC) photosensitive component of the resist material
      •  The most important element in the resist
      •  Gives the function of the resist (positive or negative)
    • Additives: controls the resist material properties
  •  For positive photoresist
    • the photosensitive component is called DQN, where
      • DQ is the photoactive element

                              

      • N comes from novolac and is the matrix material

                                           

    • The reaction for positive resist is :

                                    

      •  DQ does not dissolve in base solutions, while the product of reaction after exposure to light dissolves in base solutions. Therefore the regions that were not exposed to light will remain on the substrate, while the ones exposed will disappear in the developper, exposing the substrate.
  •  For negative resists:
    • the photosensitive element has the formula: 

                                                                                                                            

    • What happens to negative resist, when exposed?
      • It gets cross-linked: and becomes less soluble in the developper

                                             

    • Main disadvantage of negative lithography: the lines get distorted due to
      •  Swelling of the lines in the organic develope
      • Shrinking of the lines after baking

1. Optical sources
2. Photoresists

pages: 1 2 3 4 5 6 7 8 9 | next

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