Hopefully others will confirm this line of thought, but I believe that
with a 10 hr etch you are likely to have problems no matter how
resistant your photoresist is to HF/BOE. Something like SU8 shouldn't
etch in HF, but it won't stay on your substrate for that long either.
Let's say conservatively that you get an etch rate of 50nm/min on your
substrate (though if it's SiO2 it will be faster). That means that after
10 hours you'll have etched 30um deep AND 30um sideways since it's
isotropic. So you'd have to have features bigger than 60 um just to keep
them from getting completely undercut. In reality you could get much
faster etching and minor delamination problems compounding to make it
all even worse.

What is it you're trying to etch for so long? Maybe there's another
approach that could be suggested.

-Joe Grogan

Wang, Yu wrote:
> Hi,
>
> I'm looking for negative photoresist that can withstand 6:1 BOE for a long
time (10 hours or longer), and would be very grateful if you could recommend any
commercial product.
>
> Thanks,
>
> Yu Wang