> Dear Sir/ma'm,
> What can I use as selective wet etchant for W? and NiSi? The underlying
dielectric is SiO2 or High- k. What is the simplest possible way to find the
etch rate?
> Thanks

You can use warm (say 50 C) hydrogen peroxide to etch tungsten without
affecting SiO2.
To find the etch rate with a single measurement,
mask off part of the film with photoresist, resist pen, or even Kapton tape.
Etch. Clean the masking layer off. Measure the step height with a
profilometer (e.g., Dektak or AlphaStep).
    --Kirt Williams, Ph.D.   consultant