I have tryed use the 48% HF to etch the silicon
nitride. It seems even using that concentration, the
etch rate is still low. Thus I will suggest you use
dry etch instead if available. If you can not access
any dry etch machine or it is not compatible to your
process, I would say try to use the HMDS promoter
first before you spin your PR. What is your substrate?
The adbension between the PR and different substrates
are different, thus you can change to another
substrate if possible. Hopefully it helps.

Chen

> 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 ?