Surface Cleaning

Almost any surface carries deposite layers of extrinsic substances if the substrates are completely new produced as well as if deposited for longer periods. Usually they are very thin and invisible, however they inhibit subsequent treatment significantly or may cause problems in further processes:

 

There are various surces for such surface deposites:

 

  • release agents (grease, olil, waxes, silicons, any kind of hydrocarbons)
  • subsequent deposited hydrocarbons,  air suspended particles, fingerprints
  • moisture deposites
  • decomposition, oxidation and weathering of the surface
  • dust (organic or mineralic)

conventional cleaning methods

  • dry cleaning by wiping, blowing, sucking
  • wet cleaning by aid of water and solvents
  • wet etching 

drawbacks of all of these methods:

  • All of these methods cannot completely be effective in caverns, undercuts, slits
  • Remains of liquid cleaning agents may remain in caverns and slits for long time
  • Many of these conventional cleaning processes are selective. Not all substances can be removed by one single process. Various subsequent processes may be required.

Surface cleaning by plasma treatment

Etching rates are smaller in case of plasma treatment compared to wet chemical treatment. Therefore a pretreatment process applying liquid chemicals may be beneficial.

The main benefits of dry cleaning by plasma treatment are:

  • complete absence of harmful chemistry.
  • No cleaning agents need to be removed, no drying process. Subsequent treatment is possible immediately after the cleaning process
  • all surfaces in sllits, caverns and undercuts are accessable for the process.

Typical plasma cleaning processes include:

  • Degradiation of hydrocarbons (grease, oil, realease agents, silicons) by oxygene plasma or eben air plasma
  • Degradiation of oxidized surfaces by hydrogene plasma
  • Degradiation of all substances independent from their chemical nature my ion etching (IE) with argon plasma. Non-selective process which removes almost any substance which cannot be removed by oxygene plasma cleaning.

For further details study ⇒ Plasma Cleaning.

If oxygene plasma treatment continues after complete cleaning, non polar surfaces will be activated and will become wettable.

(⇒ Plasma Activation)

If plasma treatment further continues the surface starts to be etched.

(⇒ Plasma Etching)