Silicon Etchants

From Ghandhi, SK, VLSI Fabrication Principles, Wiley, 1983

Polishing Etches

• CP-4A 80 microns/min
  • 3 ml Hydrofluoric Acid
  • 5 ml Nitric Acid
  • 3 ml Glacial Acetic Acid
• Planar Etch 3 microns/min
  • 2 ml Hydrofluoric Acid
  • 15 ml Nitric Acid
  • 3 ml Glacial Acetic Acid
• almost neutral etch 0.7 microns/min
  • 10 ml Hydrogen Peroxide
  • 3.7 g Ammonium Fluoride
  • 2 ml Hydrofluoric Acid
  • 1 ml Potassium Permanganate (6%)
• 0.3 - 0.4 microns/min
  • 50 ml Hydrofluoric Acid
  • 100 ml Nitric Acid
  • 150 Glacial Acetic Acid
  • 3 g Iodine

Buffered Etches for Silicon Dioxide

• buffered oxide etch (BHF) 1000-2500 A/min at 25C
  • 28 ml Hydrofluoric Acid
  • 113 g Ammonium Fluoride
  • 170 ml DI Water
• Slow BHF 800 A/min at 25C
  • 1 ml BHF
  • 7 ml DI Water
• P-etch, 128 A/min at 25C
  • 15 ml Hydrofluoric Acid
  • 10 ml Nitric Acid
  • 300 ml DI Water

Crystallographic Etches for Silicon

• Dash Etch, 8 h
  • 1 ml Hydrofluoric Acid
  • 1 ml Nitric Acid
  • 10 ml Glacial Acetic Acid
• Sirtl Etch for <111> Silicon
  • 1 ml Hydrofluoric Acid
  • 1 ml Chromium Trioxide (5 molar in water)
• Secco etch for <100> and <111> silicon, 5 min
  • 2 ml Hydrofluoric Acid
  • 1 ml Potassium Chromate (0.15 molar in water)
• Wright Etch for <100> and <111> silicon, 5 min, long shelf life
  • 60 ml Hydrofluoric Acid
  • 30 ml Nitric Acid
  • 60 ml Glacial Acetic Acid
  • 60 ml DI water
  • 30 ml of solution of 1 g Potassium Chromate in 2 ml of water
  • 2 g Copper Nitrate (Cu NO3)2. 3H2O
• Silver Etch, for faults in Epitaxial layers
  • 2 ml Hydrofluoric Acid
  • 1 ml Nitric Acid
  • 2 ml Silver Nitrate (0.65 molar in water)
• for p-n junction delineation, 1 min
  • 200 ml Hydrofluoric Acid
  • 1 ml Nitric Acid

Cleaning Solutions

• Organic Cleaning
  • Hot Trichloroethylene or Xylene
  • Mechanical Scrubbing, ultrasonic, gas jets
• Rinse in hot DI water
• Solution 1; 10-20 min at 80 C agitated (N2)
  • 1 ml Ammonium Hydroxide
  • 1 ml Hydrogren Peroxide
  • 5-7 ml DI water
• Solution 2; 10-20 min at 80 C agitated (N2)
  • 1 ml Hydrochloric Acid
  • 1-2 ml Hydrogen Peroxide
  • 6-8 ml DI water