What are typical process pressures during plasma treatment?

[hoegs]

In general physical processes require lower pressures (100 – 250
mTorr) than chemical processes.

Physical plasma cleaning requires that the energized particles impact
the substrate surface prior to deactivation through collisional
de-excitation.

If the process pressure is high, the energized particle will experience
large numbers of collisions with other particles prior to arrival at
the bond pad, thus reducing its cleaning capability.

The distance that the energized particle travels prior to a collision
is known as the “mean free path” of the particle and is inversely
proportional to pressure.

Physical processes require low pressure in an effort to maximize the
mean free path thus maximizing bombardment impact.

Chemical processes use the plasma generated gas phase radicals to
chemically react with the compounds on the sample surface to produce
gas phase byproducts that are subsequently pumped from the plasma
system.

Chemical processes rely on the chemical reaction of the plasma
generated gas phase radicals with the substrate surface and use higher
pressure (250 – 800 mTorr).

The use of higher process pressure in chemically reactive plasma
processes is due to the need for a high concentration of reactive
species at the substrate surface.

A typical gas used for physical cleaning is Argon, (Ar). A typical gas
used for chemical cleaning is Oxygen, (O2).