Hello Mikael,
which is borofloat etch rate ? Which primer do you use ?

Best regards,
Andrea.

> Hi.
>
> Have you tried putting a few hundred nm of chromium under the photoresist?
> That work's like charm for me when etching borofloat. Without the chromium
> the photoresist peels off almost immediately but with chromium as an
> adhesive layer I can etch at least 250 µm before getting pitting. The
> photoresist I'm using is more or less "standard" positive resist, I think
> it's the Shipley 1813, and it's usually about 0.5-1 µm thick.
>
> I'm usually using a HF:HNO3:H20 mixture of 100:28:72 but there are other
> recipes out there as well. I've read a couple of papers that say you get a
> smoother etch if you mix the HF with HCl but in my experience that attacks
> the photoresist fairly fast and limits your etch depths.
>
> I hope this was of some use :)