In my experiment, sputtered Ti/Au works well as a protection layer in TMAH.
We make resistance in the active layer of SOI wafer. After the contact holes
are etched by BOE, Ti/Au(800/3000A) layer is deposited by sputtering. Then
we remove Ti/Au layer near the edge of the wafer to make sure the reserved
Ti/Au is electrical insulated from the substrate silicon by BOX oxide (the
reason why do this will be discussed later, See $$$$). After that, we back
etch the wafer in TMAH (80C 25%) for 20 hours. Finally, The Ti/Au layer is
etched to be metal wires and it works well.

$$$$: If we do not remove the Ti/Au layer on the edge of the wafer, the
Ti/Au is electrical contact with the silicon substrate which we want to
etch. In this case, TMAH do not etch the silicon. This may be caused by
primary cell effect.

In another experiment with ordinary wafer, P+ was implanted on N type
silicon to form resistance. Then Ti/Au(800/3000A) layer is sputtered and
etched to be wires. After 18 hours TMAH etching, The Ti/Au wires contact
with resistance is etched (As shown in attachment), while the isolated wires
on the oxide is good as shown attachment. We attribute this phenomenon to be
primary cell effect.