TYPES OF SPUTTERING

• DC SPUTTERING - to obtain higher sputter rates
• RF SPUTTERING - for sputtering dielectrics (the dielectric will get charged positive from the positive ions; the applied negative bias will be shadowed and therefore ineffective in attractive anymore Ar ions for sputtering processes)
• MAGNETRON SPUTTERING

  • Magnets or solenoid are put close to the target in order to keep the plasma close to the target and increase bombardment/sputtering rate

  • Types of magnetron:

    • Cylindrical magnetron - difficult to place wafers on cylindrical surfaces

    • Planar magnetron

    • S-gun

  • Target is cooled to avoid heating

• REACTIVE SPUTTERING

  • Instead of Ar, a mixture of inert and reactive gases is used in the chamber

  • The composition is controlled by modifying the partial pressure of the reactive gas

  • A compound (TiN) is formed by combining N₂ gas with a target of Ti

ADVANTAGES OF SPUTTERING over evaporation:

• better uniformity and step coverage due to:
  • sputtered atoms have higher energies (from ions) and therefore higher mobility on surface
  • higher pressure in the chamber
• possibility to deposit alloys easier
• possibility to control film properties by modifying bias, presure, etc
• possibility of incorporating impurities
• good adhesion due to bombardment
• possibility to have in-situ cleaning (clean the substrate inside the reactor before deposition by plasma etch, without breaking the vacuum)

ADVANTAGES OF EVAPORATION over sputtering:

• higher deposition rate
• no damage to substrate
• cheaper