piranha clean

Piranha clean is a highly oxidizing mixture of sulfuric acid and hydrogen peroxide for aggressive organic contamination removal. **Recipe**: Typically 3:1 to 7:1 ratio of H2SO4 : H2O2. Extremely exothermic - generates heat on mixing. **Temperature**: Self-heats to 90-150 degrees C. Some processes use external heating. **Mechanism**: Generates reactive oxygen species (atomic oxygen, hydroxyl radicals) that oxidize all organic material. **What it removes**: Photoresist, organic residues, heavy organic contamination that SC1 cannot handle. **Why piranha name**: Attacks organics voraciously like piranha fish. Aggressive chemistry. **Safety**: Extremely dangerous - reacts violently with organics, can detonate with some solvents. Strict safety protocols required. **Usage pattern**: Often first step before RCA clean when wafers have heavy organic contamination (post-photoresist strip). **Limitations**: Does not remove metals (may even deposit sulfur). Usually followed by SC2 or HF clean. **Alternatives**: Ozone-based strips, plasma ashing - safer alternatives gaining traction. **Handling**: Must never contact acetone, IPA, or other organics. Dedicated equipment.