The best known method to put a 2 um thck layer of a polymer on to a round surace is to spin coat it. The UV sensitive photoresist is made of  polymeres wich is dissolved in an organic solvent. When the solvent are dried the residue, the photosensitive polymere, are left as a smooth thin dry layer.  By pouring  the liquid at the center of a fast rotating  substrate the centrifugal force  will create a  high quality layer. Still today this manuacturing method is the choice  for almost all silicon wafer productions.  Square substrates wich can´t be rotated fast, other methods can be used.

A tremendous problem was the handling of  more then 20 different sizes in the production plant. Also handling of thin 0,1mm glass substrates made automation very tricky. A simple solution was manually deposition of each substrate.

An operator  manually spin coat  substrates. After this is done  post
baking is done on a heat plate to remove the residue of solvents.


A nice photoresist were used, shipley S1818, This is a standard all purpose type for g, h and i line exposure.
 Data of the photoresist (pdf-file)

Some efforts were made to automate the deposition and a PLC controlled system for the deposition was developed. It worked at some level but photoresist is a very tricky liquid and very small amount of  impurities makes the distribution of the liquid very tricky.  This issues were never fully solved.

Short film from the operation of the photoresist robot. Appr 7Mbyte.


A photoresist robot were tested.