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Materials to Etch Etchants
Silicon  
Polycrystalline Silicon (Si)
  1. Hydrofluoric, nitric, acetic acids and iodine
  2. Potassium hydroxide
  3. Ethylene diamine/catechol
  4. Ammonium fluoride, glacial acetic and nitric acids
Silicon Dioxide (SiO2)
  1. Buffered oxide etch (BOE) - Hydrofluoric and ammonium fluoride
  2. BOE, ethylene glycol, monomethyl ether
  3. Hydrofluoric and nitric (P-etch)
Silicon Nitride (Si3N4)
  1. Phosphoric and hydrofluoric
CVD Oxide or Pad Etch
  1. Ammonium fluoride, acetic and hydrofluoric acids
Metals  
Aluminum (Al)
  1. Phosphoric, nitric, acetic and hydrochloric acids
Chromium/Nickel (Cr/Ni)
  1. Ceric ammonium nitrate and nitric acid
  2. Hydrochloric and nitric acids (aqua regia)
Gold (Au)
  1. Hydrochloric and nitric acids (aqua regia)
  2. Potassium iodide (KI)
  3. Potassium cyanide (KCN) and hydrogen peroxide (H2O2)
  4. Ferric chloride (FeCl3) and hydrochloric acid
Silver (Ag)
  1. Ferric nitrate (FeNO3) and ethylene glycol
  2. Nitric acid


Compound Formula Standard Concentration (%)
Acetic acid CH3COOH 36
Glacial acetic acid CH3COOH 99.5
Ammonium fluoride NH4F 40
Hydrochloric acid HC 36
Hydrofluoric acid HF 49
Nitric acid HNO3 67
Phosphoric acid H3PO4 85
Sulfuric acid H2SO4 96
Potassium hydroxide KOH 50 or 10
Sodium hydroxide NaOH 50 or 10