In chemically amplified resists, slowed-down electrons (which can travel 100's nm) apparently form anions by dissociative electron attachment. The anions go on to draw cations toward them, forming the compound which can subsequently be decomposed or crosslinked.
These critters can come about pretty easily, even unintentionally. All you need is a transmitted radiation energy that exceeds the workfunction of an underlying layer, and a distance of a few hundred nm.
Unwanted exposure from these electrons reduces the contrast and increases the LER.
Japanese Journal of Applied Physics, Vol. 44, pp. 3908-3912 (2005)
Journal of Vacuum Science & Technology B, Vol. 23, pp. 2716-2720 (2005)