Acid neutralization treats acidic chemical waste streams from semiconductor wet process tools to safe pH levels (6-9) before discharge to the municipal wastewater system, as required by environmental regulations.

Waste Sources

• HF (Hydrofluoric acid): From oxide etching and cleaning. Most hazardous—requires special treatment • H₂SO₄ (Sulfuric acid): From SPM cleans and piranha strips. High volume • HCl (Hydrochloric acid): From SC-2 cleans and metal etching • HNO₃ (Nitric acid): From metal cleaning and silicon etching • H₃PO₄ (Phosphoric acid): From nitride etching

Neutralization Process

Step 1 - Segregation: Acid and base waste streams are collected separately (never mix HF with other acids). Step 2 - Collection: Waste flows to holding tanks in the sub-fab. Step 3 - Neutralization: Controlled addition of NaOH (caustic soda) or Ca(OH)₂ (lime) to raise pH. Step 4 - pH Monitoring: Continuous pH sensors control reagent dosing to maintain discharge pH 6-9. Step 5 - Settling/Filtration: Remove precipitated metal hydroxides and solids. Step 6 - Discharge: Treated water to municipal system or recycling.

HF Special Handling

HF is treated separately with Ca(OH)₂ to precipitate CaF₂ (calcium fluoride). CaF₂ sludge is dewatered and disposed as solid waste. Fluoride discharge limits are typically < 10-20 ppm.