Heated phosphoric acid is used for removal of silicon nitrides. 

Link to Silicon Nitride Wet Etch, clean, module

Link to Silicon Nitride Wet Etch, flexible, module

Processing Technique Equipment name & NEMO ID Cleanliness Primary Materials Etched Substrate Size Notes Stylus Tip Radius
Silicon Nitride Wet Etching, Wet Chemical Processing Wet Bench Clean_res- hotphos
wbclean_res-hotphos 		Clean

Resist should have been removed