This skin is believed to be several hundred nm thick depending on circumstances , and generally is the part that makes resist removal so difficult. The resist underneath the skin is usually much easier to remove. One can view the top surface skin, as being a cross-linked polymerized layer that results from exposure to implantation or plasma etching. The material under the skin is generally only modified by thermal affects, and hence may be removed with standard methods. For resist like this, one can generally start with a short min RIE with O2. If one has access to an RIE with good back side cooling Helium cooling, for example , then use that to avoid further heating of the resist.