METHOD FOR PREVENTING COLORING OF AMMONIA WATER

PROBLEM TO BE SOLVED: To effectively prevent the coloring of ammonia water to be used for washing a silicon wafer by putting the ammonia water contg. an org. complexing agent having a structure in which OH groups bond to an arom. group in the presence of an inert gas. SOLUTION: Ammonia water contg. an org. complexing agent having a structure in which two or more OH groups bond to an arom. group is put in the presence of an inert gas. The org. complexing agent may be catechol, hydroquinone, resorcinol, pyrogallol or tiron but catechol excellent in chelating effect is effectively contained. The inert gas may be nitrogen, argon or helium but nitrogen is generally used. Since dissolved oxygen in the ammonia water causes coloring, purified nitrogen obtd. by removing oxygen to the utmost is preferably used.