Hi Li,

   I would try using photo resist as the aluminum can redeposit and affect
the etch quality.  When etching in this case you should probably try to
minimize the etch pressure (to minimize undercut).  Probably an ICP source
would be preferable to a capacitively coupled source.  That said, some
groups like to use ion milling for features of this size with a 1:1 aspect
ratio.

Cheers,
   Michael

On Wed, Sep 21, 2011 at 9:29 PM, Li. Zhang  wrote:

> Hi all,
>
> Does anyone use RIE silicon etching for features under 200nm dimension?
>
> I'm using evaporated Aluminum as mask and silicon substrate. The width of
> desired features ranges from 100nm to 200nm. I've been trying SemiGroup RIE
> (recipe: SF6 15sccm; O2 7.5sccm; 30mTorr; 100W) and Trion RIE (recipe: CF4
> 25sccm; ICP Power 300W; RIE Power 90W; 20mTorr). However, I always
> experience terrible transfer from mask to substrate. For example, for a
> 200nm wide slot pattern with straight edges, after RIE, the edges become no
> straight anymore. What even worse is certain parts of the substrate have
> been successfully etched away, others are not. The depth of the etch may
> range from 20nm to 80nm. If the slot width is less than 200nm, like 150nm,
> the substrate barely got etched.
>
> The lab manager told me the dimensions I'm trying to etch may be
> challenging
> for this equipment. I'm just wondering if this problem is a recipe-related
> issue or just because the regular RIE equipment is incapable in etching
> such
> small features. Actually, I have couple AFM images that might be helpful to
> better illustrate the problem. I'm happy to share it with you via email.
>
> Any thoughts would be highly appreciated!
>
> Thanks,
> Li