Nathan,

If you want to avoid etching you may be able to use positive photoresist and
reflow the resist to create a hemispheric channel profile.

The procedure is relatively easy, and I've done it once for testing purposes in
under a day several years ago. A thick positive resist like SPR220 processed and
developed conventionally, and then heat up above the Tg of the photoresist and
it should reflow nicely. I did 220 °F in an oven for reflow, but it can be done
on a hotplate as well.

http://zeus.phys.uconn.edu/halld/diamonds/BNLdev-1-2009/JVB000130.pdf

Really it's quite easy.

Sincerely,
Dave C.


-----Original Message-----
From: Nathan McCorkle [mailto:nmz787@gmail.com]
Sent: Friday, September 20, 2013 3:40 AM
To: mems-talk
Subject: [mems-talk] Are there any 'safe' (non-hf) isotropic etches?

I'm working on microfluidics and think I can use PDMS castings
directly on my photoresist for square channels, but the resist looks
like swiss-cheese up close when it's defocused to create a curved
profile, so I think my only option is to pattern then isotropic etch,
ash/wash away resist, then cast with PDMS.

Seems that HF based solutions are my only google hits...I've used HF
once or twice before and the local lab I plan on working in has HF
already, but I remember being pretty wary of the HF. I occasionally
bump or spill things, not /that/ often, but I'd rather play with safer
chems if possible. I guess driving my car might be more dangerous
statistically, but I feel there's a little more wiggle room in
something like driving!

Anyway, any recommendations would be great. I don't have any process
setup yet so I'm flexible.

--
-Nathan

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