Sources used in evaporation

• resistive heating
  • based on heating a filament by passing a current (Joule energy)
  • disadvantages: outgassing and evaporation of wire

• inductive
  • used for refractory metals
• rf heating
  • used for dielectrics
  • RF induces eddy currents which heat the source
  • problems with contamination

• electron-bombardment heating
• laser evaporation
  • Description: A target is exposed to a laser beam, energy is absorbed, causing excitation of atoms and evaporation. A plume of radicals, ions, molecules is formed. The substrate is immersed in this plume for coating.
  • History: developed in 1970
  • Disadvantage: this method is highly directional and therefore the main problem is the uniformity of the deposited layer

    • To improve uniformity several techniques are used:

      • rotating and scanning the wafer

      • placing a mirror in the laser beam, thus the spot on the target that is hit by the laser beam becomes larger, enlarging the plume

  • Multiple sources are used for deposition of alloys or multilayered films.