STEP COVERAGE

Can be improved by:

• heating the substrate, although this method must be used with care, due to the fact that:
  • reactions may occur at Al/Si interface due to high temperature and a barrier material may be required between the two materials (Al and Si) to avoid reactions
  • the grain structure is modified by the temperature, grains can be bigger and the resulted film can be rougher
• force fill
• biasing the substrate - bias sputtering

• • A bias is applied on wafer in order to atract Ar ions and:

    • clean the substrate and remove native oxide

    • sputter deposited material in the trench and redeposit it on the sidewall, like in the picture below

• Disadvantages of bias sputtering:

  • the films may have higher roughness due to the succesive processes of deposition and sputtering

  • the film can get damaged for high biases, due to bombardment with high energy Ar ions

• introducing a collimator - collimator sputtering
  • the collimator has the purpose to select only the atoms that arrive perpendicular on the substrate, stopping the atoms which arrive at higher angles

  • Disadvantages of collimator sputtering:

    • deposition takes place also on collimator, thus the collimator has to be replaced periodically

    • low deposition rate on substrate due to the selection process

    • reduced sidewall coverage (see picture below)

• Ionised metal plasma
  • Sputtered atoms pass trough a plasma and become ions
  • Ions arrive at substrate, are neutralised and deposited