INFLUENCE OF INITIAL WAFER CLEANLINESS ON METAL REMOVAL EFFICIENCY INIMMERSION SC-1 CLEANING - LIMITATION OF IMMERSION-TYPE WET CLEANING

When contaminated silicon wafers are immersed in an ultra-pure cleanin g solution of an NH4OH/H2O2/H2O mixture known as the RCA Standard Clea n 1 (SC-1), in which the impurity concentration is negligibly low, the level of wafer-surface metallic contamination after the cleaning trea tment depends on the amount of metallic impurities brought into the so lution by the to-be-cleaned wafers themselves, Even if the chemicals a re disposed of after each wafer cleaning, the surface metallic contami nation Is still dominated by the amount of impurities brought into the fresh solution by the wafers themselves, In the past, purer chemicals have been sought to improve metal removal efficiency, but after reaso nably purer chemicals are obtained the efficiency is not governed by t he initial chemical purity but by the initial wafer cleanliness, Becau se of this, scrubbing of dirty wafers-both the back-and front-surfaces -before immersion-type wet cleaning is recommended, However, to meet f uture stricter wafer cleanliness requirements, new cleaning methods in which fresh chemicals are continuously supplied, such as single-wafer spin cleaning, will have to be employed.