SPM Clean -Piranha Etch or Pirhana Clean
Piranha etch is used to clean photoresist and other hard to remove organic residue from silicon wafers. For wafer cleaning, Piranha etch, is a mixture of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2)
Removal of gross organic materials from Si wafers, such as hardened photoresist polymer patterns after ion implantation, and other visible contaminants of organic nature, can be accomplished by using mixtures of H2SO4 (98 wt%) and H2O2 (30 wt%). Volume ratios of 2:1-4:1 are used at a temperature of 100-130C. Organics are destroyed and eliminated by wet-chemical oxidation, but inorganic contaminations, such as metals, are not desorbed.
Many different mixture ratios are commonly used for Si wafer cleaning. A typical mixture is 3:1 concentrated sulfuric acid to 30% hydrogen peroxide solution; other protocols may use a 4:1 or even 7:1 mixture.