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
Substrate preparation
