Have you tried a buffered oxide etch (BOE)?

http://en.wikipedia.org/wiki/Buffered_Oxide_Etch

Best Regards,
Garrett Oakes

EV Group
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-----Original Message-----
From: Kvel Bergtatt [mailto:vacmitun@gmail.com]
Sent: Tuesday, April 08, 2008 11:33 PM
To: General MEMS discussion
Subject: Re: [mems-talk] PMMA etch resistance

wet etch is not an option?

_fm

On 4/7/08, Satish Yeldandi  wrote:
>
> Hi all
>
> I am trying to etch SiO2 using PMMA as mask. I am using ICP RIE system for
> plasma etching. My oxide layer is 250nm thick and the substrate is Si. PMMA
> is 180nm thick. PMMA is not holding as a mask. I am not able to etch SiO2
> with this thick PMMA. Can anyone suggest me how to etch SiO2 with this
> thick PMMA as mask.