Coagulation in Positive Photoresist and Resist Reclamation.

Abstract

We studied the coagulation which can occur in collected resist solutions and offer a resist reclamation system suitable for simple Matrix Liquid Crystal Display (SMLCD)- manufacturing lines. A lot of particles under a few μm in size are fonned in the collected solution during a roll-coating process; most particles are coagulacontaining various metal ions coming from the conditions the resist encounters. These coagula can be filtered. On the other hand, the increase in viscosity caused through the coating process is adjusted to its original state by adding a resist solvent. When the collectedphotoresist is kept at a room temperature for 50 days, needle-shaped crystals appear in the resist solution. These crystals were determined to be ammonium zinc sulfate hexahydrate by means of X-my diffraction analysis, and their formation can be avoided by carefully selecting the rubber material on the surface of rolls. When the collected resist is kept at an elevated temperature of 40°C for 100 days, bead-like coagula appear in the solution. The beads consist not only of thermally modifiedphotoactive compounds (PAC) but also of novolak resin. Areclamation system which is composed of a double cylindrical viscometer and a microfilter unit has been tested for more than half a year, and was found to perform 30.0±0.5 cP in viscosity and to reach an equilibrium on water content; about 1%.