Patent ID: 7741429

Claim:
A method of making a stable photoresist solution containing a polymer from a solution of a polymer containing trace metals, said method which consists of the steps of: (a) providing a polymer solution containing a polymer, a first solvent and trace metals; (b) passing said polymer solution through an acidic cation ion exchange material to remove said trace metals therefrom and thereby forming a polymer solution containing free acid radicals; (c) precipitating said polymer from said polymer solution of step b by contacting with a second solvent wherein the polymer is substantially insoluble therein; (d) filtering said solution and said second solvent to thereby form a solid polymer cake; (e) contacting said cake from step d with sufficient quantities of additional said second solvent in order to remove free acid radicals therefrom; (f) adding a compatible photoresist solvent to said solid polymer cake from step e and mixing the two in order to dissolve said polymer in said photoresist solvent and thereby forming a photoresist solution; and (g) removing any residual first and second solvents from said photoresist solution containing said polymer to form a stable photoresist solution.