This are a few examples of deposition methods, using liquid sources:

• spinning
• dipping
• spraying
• casting
• melting

During the deposition, there are no chemical reactions that take place, as in the case of chemical liquid deposition. The liquid source is solidified by different physical means. For example the solvent can be evaporated, resulting in a solid film.

SPINNING (spin coating)

• Definition: application of a thin film by pouring a liquid (resin) and spinning the wafer
• How is it done?
  • the wafer is placed on a rotatable chuck and vacuum is created between wafer and chuck, to avoid movement of the wafer relative to the holder
  • the liquid is dispensed in the middle of the wafer while the wafer is rotating at low velocities
  • the excess is spinned-off (leaves the wafer at the edges)
  • the spinning speed is increased so that the resin is uniformly deposited and the solvent is easily evaporated
  • the wafer will be heated at around 100oC for further evaporation and solidification of the film

• Thickness: The film thickness depends mostly on the liquid viscosity and the rotating speed:

• Applications:
  • in lithography, the photoresist is applied in this manner
  • organic membranes for sensors

More information on spin casting can be found in the lithography tutorial, when application of photoresist is dicussed.