PURPOSE: To obtain a film patternized in a high accuracy, having excellent flatness, by producing a film forming agent with specified org. solvent and silica sol soln., and by regulating the conc. of solid component to a specified amount expressed in terms of SiO2 when the film is formed.

CONSTITUTION: As the org. solvent, single or ≥two kinds of solvent selected among butylolactam or its alkyl deriv. of 200W250°C b.p., alcohols of 180W250°C b.p., having alkyl group on the side chain of phenyl group and hydroxyl group on the terminal of alkyl group, glycols of ≤250°C b.p., ethylene glycol or diethylene glycol deriv. substituted one hydroxyl group by 1W4C alkoxy group and unsubstituted another hydroxyl group, (di)ethylene glycol deriv. substituted one hydroxyl group by alkoxy group and another hydroxyl by CH3COO group and carboxylic acid ester of 150W250°C b.p. is used. The org. solvent and the silica sol soln. are combined. The conc. of solid is regulated to 5W30wt.% expressed in terms of SiO2 when the film is formed.