Processes that occur during etching

• Physical - bombardment of energetic particles, or mechanical removing of material (CMP)
  • Selectivity = 0 (attacks all materials)
  • Anisotropic (attacks only in the direction in which particles are coming)
• Chemical - chemical reactions occur between etchant and film, and the result product is removed
  • Selectivity = 1 (attacks only the material with ehich it can react)
  • Isotropic - the material is etched in all directions (chemical reactions take place wherever the reactants are)
• Both - sometimes both mechanisms appear in the etching

Types of etching

• Wet etching
  • etchant is liquid
  • usually isotropic, but in some case it can be anisotropic
• Dry etching
  • etchant is not liquid (usually it is plasma)
  • can be anisotropic or isotropic