Metal ion reduction in top anti-reflective coatings for photoresists

A method for producing a top anti-reflective coating composition having a very low level of metal ions consisting essentially of:

• a) treating an acidic ion exchange resin with deionized water, washing said ion exchange resin with a mineral acid solution and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 200ppb each;
• b) providing a solution of 5 to 40 weight percent of a water soluble organic carboxylic acid polymer having a molecular weight of from about 500 to about 100,000 in a suitable solvent;
• c) rinsing the ion exchange resin with a solvent which is the same as or at least compatible with the solvent for the .component or mixture of components which is to be treated with the ion exchange resin and thereby substantially removing water and saturating the ion exchange resin with said solvent;
• d) passing the water soluble organic carboxylic acid polymer solution through the ion exchange resin and thereby reducing the level of sodium and iron ions in the solution to less than 100 ppb each;
• e) formulating a top anti-reflective coating composition by providing an admixture of:
• (1) the treated water soluble organic carboxylic acid polymer;
• (2) a fluorine containing water sparingly soluble organic C.sub.3 -C.sub.31 aliphatic carboxylic acid;
• (3) an ammonium hydroxide;
• and
• (4) a suitable solvent.