Influence of initial wafer cleanliness on metal removal efficiencyin immersion SC-1 cleaning: limitation of immersion-type wet cleaning

摘要

When contaminated silicon wafers are immersed in an ultra-purencleaning solution of an NH4OH/H2O2/Hn2O mixture known as the RCA Standard Clean 1 (SC-1), in whichnthe impurity concentration is negligibly low, the level of wafer-surfacenmetallic contamination after the cleaning treatment depends on thenamount of metallic impurities brought into the solution by thento-be-cleaned wafers themselves. Even if the chemicals are disposed ofnafter each wafer cleaning, the surface metallic contamination is stillndominated by the amount of impurities brought into the fresh solution bynthe wafers themselves. In the past, purer chemicals have been sought tonimprove metal removal efficiency, but after reasonably purer chemicalsnare obtained the efficiency is not governed by the initial chemicalnpurity but by the initial wafer cleanliness. Because of this, scrubbingnof dirty wafers-both the backand front-surfaces-before immersion-typenwet cleaning is recommended. However, to meet future stricter waferncleanliness requirements, new cleaning methods in which fresh chemicalsnare continuously supplied, such as single-wafer spin cleaning, will havento be employed