Ozone water combines DI water with dissolved ozone gas for environmentally friendly cleaning and oxidation. Ozone source: Generated on-site from oxygen using corona discharge or UV. 20-100+ ppm concentrations in water. Mechanism: Ozone (O3) is powerful oxidizer. Breaks down organics, oxidizes metals, grows thin chemical oxide on silicon. Advantages: Replaces some aggressive chemistries (piranha, SC1), environmentally benign (decomposes to O2), no chemical waste, lower cost. Applications: Photoresist stripping, organic cleaning, surface oxidation, pre-clean step. Combinations: Ozone + HF alternating treatments increasingly popular for particle removal. Ozone + megasonic. Limitations: Lower oxidizing power than piranha for thick photoresist. May need multiple steps. Process variations: Spray, immersion, or vapor phase ozone delivery. Decay: Ozone decomposes rapidly - must use near generation point. Short half-life in water. Equipment: Ozone generators, contactors for dissolution, POU delivery, ozone destruct systems for exhaust. Trend: Growing adoption as fabs pursue cleaner, safer chemistries.