HF solutions etch LPCVD Six Ny films only slowly, but etch most PECVD SiN films, which are lower quality and also have a lot of hydrogen, rapidly and can therefore be patterned with photoresist. I'm not sure where sputtered SiN falls in relation to these, but it's worth trying 5:1 BHF with your sputtered SiN. --Kirt Williams