Hi Dr. Tibrewala

Can't you use a Ni mask?! I don't now what kind of polymer you are
etching, but some time ago I had saw that someone had spread S1811
over an SU8 layer and made the Ni mask by lift off, so if you can
expose your substrate a little and put it in acetone ... it may work
good!

I hope I had helped you
 best wishes

NH