Metal ion reduction in photoresist compositions by chelating ion exchange resin

A method for producing a photoresist composition having a very low level of metal ions

• a)
• 1) washing a chelating ion exchange resin process with deionized water followed by washing with a mineral acid solution, washing again with deionized water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb;
• or
• 2) washing a chelating ion exchange exchange resin with deionized water, followed by washing with a mineral acid solution, washing again with deionized water, followed by washing with an ammonium hydroxide solution and thereby converting the chelating ion exchange resin to an ammonium salt, followed by washing with deionized water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each;
• b) removing water from the ion exchange resin of 1) or 2), followed by washing with a photoresist solvent which is compatible with the solvent in the photoresist composition to be purified;
• c) mixing a photoresist composition with the ammonium salt of the chelating ion exchange resin or the acid form of the chelated ion exchange resin and heating in the range of 30 to 90.degree. C.;
• for 1 to 80 hours, followed by filtering through a 0.05 to 0.5 .mu.m (micrometer) filter;
• and thereby reducing the level of sodium and iron ions in the photoresist compisition to less than 100 ppb each.