A structure includes a silicon layer disposed on a buried oxide layer that is disposed on a substrate; at least one transistor device formed on or in the silicon layer, the at least one transistor having metallization; a released region of the silicon layer disposed over a cavity in the buried oxide layer; a back end of line (BEOL) dielectric film stack overlying the silicon layer and the at least one transistor device; a nitride layer overlying the BEOL dielectric film stack; a hard mask formed as a layer of hafnium oxide overlying the nitride layer; and an opening made through the layer of hafnium oxide, the layer of nitride and the BEOL dielectric film stack to expose the released region of the silicon layer disposed over the cavity in the buried oxide layer. The hard mask protects the underlying material during a MEMS/NEMS HF vapor release procedure.