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 :)

/Mikael


----- Original Message -----
From: Michael A Gingras 
Date: Thursday, November 15, 2007 12:13 pm
Subject: [mems-talk] Best resist for HF etching

> Hello,
>
> Me and my colleagues are trying to etch a 4 micron Pyrex layer
> with HF using photoresist as a mask. We've seen delamination of
> the mask as seen by others. We are currently using a Shipley 7
> micron resist and 4:1 HF:H2O etch.
>
> Any recommendations on the best resist and HF concentration to
> help us get the whole film etched before delamination? Current the
> Pyrex is etching about 300A/s, so we'd need something that would
> last 2-3 minutes.
>