wet etching of SU-8 (exposed and postbacked) is close to impossible if
you
do want to prevent the rest of your sample from beeing damaged. there
are
some chemicals which can kind of swell the resist and lift it of the
substrate, but they do not work perfectly and in all cases, depends on
the
thickness and feature shape and size. A wet etching process of su-8
exists,
it uses a sulfuric acid and an electric potential to prevent metallic
parts
from beeing attacked, it was developed in Mainz, Germany, but I do not know
the exact process parameters.

J.