Which polymer are you talking about? Polyimide, photoresist, negative or
positive, and there are numerous types of polymer used in MEMS.

Oxygen RIE should etch any carbon based polymer fine. The energy of the
O will break down any carbon bonding. The directionality of RIE will
tend to have vertical walls. Of course there will be a tremendous
variation due to the exact set up of your plasma conditions, pressure,
power, space between the plates.

If silicon or some other metal is incorporated into your resist, Oxygen
plasma etching will stop as SiO2 builds up at the etch interface.

KOH will dissolve positive resist, unless you have fried the resist
(pushed the Novolak resin through two condensation reactions, at 180
deg. C) with very hot bakes. Polyimide uncured dissolves in alkali, but
after a 300 C degree bake (or would it be 350?)  it should be fairly
resistant. The sidewalls in a liquid system will be defined by the
classic radius from the edge of the masking opening, isotropic etch.

I doubt KOH will touch negative resist at all, but there are a great
many of them, so I can say this for all negative resists.

I would use O2 RIE for a polymer.

Ed

-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Hakemi, Ghazal
Sent: Thursday, March 13, 2008 5:02 AM
To: mems-talk@memsnet.org; mems-talk@memsnet.org
Subject: [mems-talk] Isotropic / anisotropic polymer etch

Dear all,

Does anybody know how polymer etches  (isotropic or anisotropic) in:

1.
        Oxygen-based RIE
2.
        KOH (potassium hydroxide)

Any details are appreciated.