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.