Detail: KOH or NaOH and special additive is applied for anisotropic etching in order to fabricate a pyramid structural surface for reduce light reflection and remove the mechanically damaged layer and metal residues. But process bath of Monocrystal and Polycrystal will be difference so Monocrystal it used alkaline corrosion and Polycrystal it used Acidic corrosion for reaction. So react off Monocrystal will have reflection about 10% but Polycrystal will have reflection about 25% (Monocrystal it better than). which: Alkaline Bath: Reaction equation => Si + 2KOH + H20 K2SiO3 + 2H2 Acidic Bath : Reaction equation => SiO2 + 2HF H2SiF6 + 2H2O HCL will react with metal ions so remove the ions from the wafers.