sc2 (standard clean 2)

SC2 (Standard Clean 2) is a hydrochloric acid and hydrogen peroxide solution that removes metallic contamination from silicon wafer surfaces. **Recipe**: Typically 1:1:6 to 1:2:8 ratio of HCl : H2O2 : H2O. Also called HPM (Hydrochloric Peroxide Mixture) or RCA-2 clean. **Mechanism**: HCl dissolves and complexes with metal ions (Fe, Al, Mg, Na, etc.), preventing redeposition. H2O2 maintains thin oxide layer. **Temperature**: Usually 60-80 degrees C. Similar to SC1 operating conditions. **What it removes**: Alkali metals, transition metals, heavy metals deposited during prior processing or from SC1 chemicals. **Does not remove**: Organic contamination (thats SC1s job). **RCA sequence**: SC1 first (organics, particles), HF dip (optional, removes oxide), then SC2 (metals). Order matters. **Compatibility**: Safe for silicon and thermal oxide. May attack some metals - used before metallization. **Modern usage**: Still widely used but increasingly replaced or supplemented by other approaches at advanced nodes. **Quality**: Chemical purity critical - metals in SC2 chemicals would contaminate wafers.