Please see the paper below.
They used high density O2 plasma in a barrel plasma system and got the under
etch rate of 4 um/min.

Polyimide sacrificial layer and novel materials for post-processing surface
micromachining
A Bagolini, L Pakula, T L M Scholtes, H T M Pham, P J French and P M Sarro
J. Micromech. Microeng. 12 No 4 (July 2002) 385-389

Best regards.

Daniel Sang-Won Park
Graduate Research Assistant
UTD MiNDS (http://www.utdallas.edu/~jblee/research/index.html) Lab
[Cell] 214-952-8649, [Fax] 972-883-6839
[E-mail] [email protected]
[Web] http://www.utdallas.edu/~spark



----- Original Message -----
From: "Dongmei Li" 
To: 
Sent: Wednesday, June 02, 2004 6:13 PM
Subject: [mems-talk] Polyimide etching


>
> Dear All,
>
> Does anybody out there know what is the best approach for polyimide
etching?
> What I need to etch is PI-2555 from DuPont and the coated PI-2555 layer is
> about 1 micron.
>
> I only have tried dry etching (RIE) with CF4:O2, which gave me a very slow
> etching rate. FYI, the photoresist and developer I used are AZP4210 and
> AZ400K, respectively.
>
> Now I am about ready to try RIE again using just O2, but not quite sure
how
> much of a difference it's going to make in terms of etching rate. So, any
> information regarding this will be helpful for me so that I don't have to
> repeat somebody else's failure. :)
>
> Thanks a bunch!
>
> dongmei
>
> Dongmei Li
> Postdoctoral Fellow
> University of Colorado
> Department of Chemical and Biological Engineering
> Campus Box 424
> Boulder, CO 80309
> 303-492-8547 (office)
>
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