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Realizing environmentally benign silicon-wafer cleaning has become one of the most important topics in the semiconductor industry. We have developed an ultra-diluted HF/nitrogen-gas jet spray procedure for single-wafer spin cleaning, which can efficiently remove not only particulate but also metallic contaminants in 20 s from both silicon and silicon-dioxide surfaces without causing damage to fragile 45-nm wide polycrystalline-silicon gate structures. The use of a very low HF concentration makes the silicon and oxide losses negligible, below 0.003 and 0.03 nm, respectively. This simple, single-step, single-wafer Spin CLeaning with use of Ultra-Diluted HF/nitrogen jet spray (SCLUD) drastically reduces the chemical and water consumption as well as electrical energy per wafer due to the short spraying time with the ultra-diluted HF at room temperature. HF wastewater, the only effluent of this cleaning, is recycled by forming Ca[F.sub.2], which can be a raw material for HF or Portland cement. This cleaning, therefore, meets the requirements with respect to the environmental control. Index Terms--Jet spray, RCA cleaning, single-wafer spin cleaning with repetitive use of ozonated water and diluted HF (SCROD), single-wafer spin cleaning, single-wafer spin cleaning with use of ultra-diluted HF/nitrogen jet spray (SCLUD).

When contaminated silicon wafers are immersed in an ultra-pure cleaning solution of an N[H.sub.1] OH/[H.sub.2][O.sub.2]/[H.sub.2]O mixture known as the RCA Standard Clean 1 (SC-1), in which the impurity concentration is negligibly low, the level of wafer-surface metallic contamination after the cleaning treatment depends on the amount of metallic impurities brought into the solution by the to-be-cleaned wafers themselves. Even if the chemicals are disposed of after each wafer cleaning, the surface metallic contamination 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 reasonably purer chemicals are obtained the efficiency is not governed by the initial chemical purity but by the initial wafer cleanliness. Because of this, scrubbing of dirty wafers - both the back- and front-surfaces - before immersion-type wet cleaning is recommended. However, to meet future 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.