> Anyone knows good wet or dry etching method for etching SU8 from Nickel
> structure ?

I have some experience of SU8 dry etching of 5um depth and 2um size with
thin (<1um) metal mask.  I hope my recipe help you.

You can remove SU8 with O2 RIE.  Pure O2 etching is anisotoropic.  The
rate was moderate(200nm/min, 30Pa O2, 200W RF) in my chamber.  You may
found some residual filaments of sub-um diam, um length after RIE
process (the filaments may not be seen with optical microscope).  Side
wall is not smooth in the scale of sub-micrometer.

When 5-10% SF6 is added, etching rate is higher than the rate of pure O2
etching.  Etching profile is isotoropic, side wall is smooth, and the
amount of residual is small.

Best regards,

Shigetomo Shiki