Hi all, i need to pattern a 400um thick silicon nitride film.
I'm planning to use BHF (1:7) to remove silicon nitride from unwanted areas.
Etch rate of silicon nitride is about 1nm/min, so the etch time will be
about 400 min.
About photoresist: i've tried to use s1813, but it peel off after about 5
hours etch.

Here is the procedure i've followed:
spinning of primer
spinning of s1813
soft bake (2 min at 120 °C)
photolitography
hard bake (2 min at 120 °C)

How can i improve s1813 resistance to BHF? May a thicker s1813 layer help
? Or a longer hard bake time ?
Any idea about an alternative photoresist ?

Best regards,
Andrea