Hello,

If you have enough Ni as mask material (you did not specify your Ni
thickness...), you may want to try ion milling. I am very satisfied with the
results from ion milling, the only problem was the edge roughness issues in the
end of the ion milling process. However, if you have large features, the edge
roughness should not be a problem at all.

Bests,

Mehmet Yilmaz
Mechanical Engineer