The step in photolithography which follows exposure is development. The development process is used with both positive and negative photosensitive polymers. There are two different methods of development:
- Immersion development
- Spray development
In immersion development, the substrate is dipped in a holding tank containing the development chemicals. Immersion development can be performed with the substrate positioned either horizontally or vertically. In spray development, spray nozzels are used to force the developer onto the substrate. The substrate passes under the nozzels on a horizontal conveyer.
The object of the development step is to remove the exposed region (for positive materials) or the unexposed region (for negative materials) at a faster rate, R, than the background, Ro, in a reproducible, controlled manner.
Since the develop time is a function of the exposure time or dose, R is given by:
- R=Roe-akI
- where:
- I is the intensity of exposure
- a is the energy absorption coefficient, and
- t is the exposure time.
- The exposure energy E, or dose, is given by:
- E = It
Development rates are also dependent on pre-bake time and temperature, the concentration or type of developer used, and the developer temperature.