acid neutralization

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**.