Hi,

  I am trying to wet etch multilayer thin metal film with photoresist
protective patterns on top. The metal film was grown in UHV sputter
chamber and is composed of Ta, NiFe, Cu, CoFe, FeMn, Ta from bottom to
top. They add up to no more than 50nm thickness. I tried with Chrome
etchant 18, but found it could hardly etch anything. I then put the
sample in 7% HNO3, although part of the metal film was gone, still
some very thin 'membrane's left.

  I am trying to find a kind of wet etchant that can clean such
multilayer thin metal film nicely with little attack to resist. Does
anyone have clue?