Your BHF etch rate for silicon nitride seems way too low. Your BHF is
quite concentrated. I would first investigate the effectiveness of your
BHF first. As you soak your wafer for such a long time (5-6hrs), it's easy
to peel off photoresist through weak local adhesion on the edges and
pinholes in resist. If your BHF is not that weak, you may not run into
this problem at all...

Isaac


On Thu, 16 Aug 2007, Andrea Mazzolari wrote:

> 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 ?