you can try etching it in an Oxygen environment with a 120mT pressure.
>From: Giuliano Gregori
>Reply-To: General MEMS discussion
>To: General MEMS discussion
>Subject: [mems-talk] polyimide dry-etch
>Date: Wed, 25 Jan 2006 11:56:49 -0800
>
>
>Hello everybody,
>what's a good process to dry-etch a HD 8820 polyimide sacrificial layer 2-3
>micron thick ?
>Thanks in advance !
>
>Giuliano