|WikiProject Chemistry||(Rated Stub-class, Low-importance)|
"Plasma Ashing" and "Fluorine" does not really fit together, although the reaction with fluorine is often an oxidation reaction. However, this seems not to be meant here. In fact, fluorine itself and fluorine atoms originating from fluorine containing precursors are broadly used for "Plasma Etching" / "Thermal Ething" e.g. in semiconductors. Unfortunately both key words are missing. The term "etching" appears, though, but the discussion is currently limited to etching by wet acids. Even here an extension to the other etching regimes such as etching by basic agents or complexing media is needed. Furthermore, the use of "Plasma Ashing " is not limited to resist removal in semiconductors. "Plasma Ashing" is also broadly used e.g. in analytics to oxidise organic materials.
Difference between charged and non-charged radicals
It seems to me that the article has trouble differentiating between free radicals, charged radicals and neutral radicals. I am only minimally familiar with this subject matter but from what is included in the article already it appears that the charged radicals are what is referred to as "free radicals" in the second paragraph, and I suggest chainging free radical to charged radical for clarity. --Pyrophreek 1/28/2012
Resist is removed to prepare the wafer for the next deposition or lithogrpahic step.
I recently wrote something down about plasma ashers, please comment:
An oxygen plasma asher can have one of the following configurations:
· Barrel reactor
· Downstream stripper
· Parallel plate system
A barrel stripper has two moon-shaped electrodes around a barrel shaped specimen holder. The plasma is created everywhere and ion-bombardment takes place everywhere.
A parallel plate system is the simplest design, anisotropic bombardment more related to sputtering or reactive ion etching (not often used).
A Downstream stripper is a configuration in which the plasma is created in a separate area from the specimen chamber, after which the reactive gases are transported to the specimen.
What sets a plasma asher apart from other chemical dry etching techniques is that the number of charged particles is minimized in an asher. All three configurations have different methods to reduce ion bombardment.
In a barrel asher and parallel plate asher this can be done by use of metal perforated sheets to reduce the line-of-sight bombardment, effectively creating a triode setup. The charged particles would get attracted to the grounded perforated sheets while the radicals can diffuse toward the wafer.
In a downstream asher one can place perforated plates above the wafers to remove line-of-sight bombardement. The flow would only transport radicals past the grid-plates. These grid-plates can produce an air pocket above the centre of the wafer, which has the effect of a higher etch-rate at the edges. This can be reduced by purchasing grid-plates with larger holes towards the centre than around the edge.
Ref: Fundamentals of Microfabrication, Marc Madou