Hi,

If you are asking about PMMA as mask to etch underneath SiO2, It is
possible. The only issue I have observed is the poor adhesion between both.
This results in poor edge definition of oxide, after etching. BHF creeps
through the interface, and results in a big "crater", than original PMMA
mask. Ultimately it results in whole PMMA layer peel off(but it never reacts
with BHF). But I could do till 300nm oxide using this, with compromised
edges. Also I found that hard baking of PMMA slightly improves the etch
resistance.

I think in your case a thin 950K layer will be enough, I think.

Best Regards,

Sangeeth

On Tue, Jul 5, 2011 at 5:53 PM, righeira carnegie wrote:

> Hi,
>       I am not sure, but is it possible to attack SiO2 with PMMA ?, i dont
> think so, because it forms a bilayer, it does not react. For nanoimprint, I
> gone through some paper, they do selective etching having 2 layers. If at
> all if you want to isotropically etch SiO2, best way is to do this Reactive
> Ion etching, its easy and simple for isotropic. Check it out and let me
> know. if at all you succeed in etching SiO2 with PMMA, let me know as well.
> Thank you
>
> Righeira

--
*Sangeeth K