If only aluminum is exposed on the wafer after ion milling I would suggest
using a fluorine etch CF4+ O2 to remove the fences in your rie system. The
fluorine won't attack the Al much and it should remove the Carbon left behind
from your milling process. You might also try doing a photoresist stabilizing
with UV and temperature to harden the resist prior to ion milling. This might
provide some protection. Bob Henderson