Maybe you can etch silion by TMAH instead of KOH. I did TMAH etching with
Ti/Au layer on the silicon wafer.

After TMAH (25%, 80℃) etching for 18 hours, the Ti/Au layer on SiO2 is
fine, but the Ti/Au layer contact with silionc is etched. This is probablely
caused by primary cell. The contacted Ti/Au and silion form a primary cell,
the metal layer is etch following electrochemistry etching.

hoping it is useful for you.

Yongliang Yang