Process for producing film forming resins for photoresist compositions

A method for producing a film forming resin suitable for use in a photoresist composition, said method comprising the steps of:

• (a) providing a solution of a film forming resin in a solvent, said film forming resin made by polymerizing at least one monomer comprising a cycloolefin or an acid labile acrylate or methacrylate monomer;
• (b) providing the following two filter sheets;
• (i) a filter sheet comprising a self-supporting fibrous matrix having immobilized therein an acid-washed particulate filter aid and a particulate ion exchange resin, said ion exchange resin having an average particle size of from about 2 to about 10 μm, wherein said particulate filter aid and ion exchange resin particles are distributed substantially uniformly throughout a cross-section of said matrix;
• and
• (ii) a filter sheet comprising a self-supporting matrix of cellulose fibers having immobilized therein a particulate filter aid and a binder resin, said filter sheet not containing any ion exchange resin embedded therein, and having an average pore size of about 0.05-0.5 μm;
• (c) rinsing the filter sheets of step (b) with the solvent of step (a);
• and
• (d) passing the solution of the film forming resin through either the filter sheet of step (b)(i) as rinsed in step (c) and then through the filter sheet of step (b)(ii) as rinsed in step (c) or the filter sheet of step (b)(ii) as rinsed in step (c) and then through the filter sheet of step (b)(i) as rinsed in step (c),
• thereby producing the film forming resin suitable for use in a photoresist composition.