Environmentally Benign Single-Wafer Spin Cleaning Using Ultra-Diluted HF/Nitrogen Jet Spray Without Causing Structural Damage and Material Loss

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 CaF₂, which can be a raw material for HF or Portland cement. This cleaning, therefore, meets the requirements with respect to the environmental control.