spm (sulfuric peroxide mixture)

SPM (Sulfuric Peroxide Mixture) is a sulfuric acid and hydrogen peroxide solution used for photoresist stripping and aggressive cleaning. **Also called**: Piranha solution, Caro acid (the reactive species). Same chemistry, different names. **Recipe**: H2SO4 + H2O2, typically 3:1 to 5:1 volume ratio. Mix order matters for safety. **Reactive species**: Forms peroxymonosulfuric acid (Caro acid) - extremely strong oxidizer. **Temperature**: Self-heating to 100-130 degrees C on mixing. Process may add heating or cooling. **Applications**: Strip photoresist (especially hard-baked or implanted resist), remove heavy organic contamination, pre-diffusion clean. **Advantages**: Extremely effective for organics, removes even difficult contamination. **Disadvantages**: Dangerous, generates sulfate waste, high chemical consumption, high temperature. **Safety**: Exothermic mixing, violent reaction with organics, requires specialized equipment and training. **Processing**: Typically batch immersion. Timed process followed by rinse. **Alternatives**: Plasma ashing, ozone stripping, green chemistries reducing SPM usage at advanced nodes.