I raised the question a half year earlier or so about how far secondary electrons could travel in polymers. This week I happened upon a reference which suggests that it could be in the 100 nm range, since polymers are insulators:
J. Appl. Phys. 85, 1137 (1999).
Likewise this reference tells how electrons with energies as low as 12 eV can still go through 50 nm of the polymer resist (SAL-601).
J. Vac. Sci. & Tech. B 10, 2877 (1992).
Thanks to earlier respondents for helpful suggestions.
FC