Mary Tang mtang at snf.stanford.edu
Mon Jun 30 15:46:24 PDT 2003

Hi David --

Just additional few questions that I think the other SpecMat members are bound
to ask you as well:

1.  Where is your tungsten being deposited?  (Any processing done outside of
SNF needs to be carefully considered, because of possibly contamination
2.  Where do your wafers go after the proposed Lampoly step?  (Any other clean
3.  Do you have any literature references or experience with SF6 and the
typical profiles you get with this?  (I would strongly suggest you make an
appointment to chat with Jim McVittie, our resident etch expert...  I am
nowhere near an expert, but has understood the prevailing wisdom is that SF6
gives you lots of undercutting -- the anisotropic profiles attainable on the
Lampoly are due to the Cl2 chemistry steps.  Jim can tell you what's really
possible in our lab...)

For reference, you should check out:
http://snf.stanford.edu/Materials/NewMatProc.html  --- this lists all the
questions and issues you should consider when you want to bring something new
into the lab (some of the questions aren't applicable to your situation, but
I'm sure you can figure out which ones are...)



David Lieberman wrote:

> Hi Mary, John, Mahnaz, and Jim;
> We'd like to ask permission to use the Lampoly to etch a thin layer of
> tungsten ( ca. 100nm thick with an array of 130nm diameter holes).  We
> require an anisotropic etch ( vertical to near vertical sidewalls) and
> believe this is the only tool at SNF with the capability to resolve this
> feature.
> Since the etch chemistry creates a volatile product we believe that it's a
> safe process to run in the Lam.  The SF6 reacts with the tungsten to form
> the volatile product WF6 which is then pumped out of the system.  With the
> extremely small feature sizes, and the thin film, the amount of W actually
> etched is extremely small.
> We've talked to a fab that has used the TCP etcher, normally dedicated to
> CMOS polysilicon, for making refractory metal gates with no problems.  They
> run a few dummies with SF6 afterward just to be extra safe.
> Looking at the history of the Lampoly it is clear the tool is underutilized
> and if the process succeeds we would look to use the tool on a regular
> basis.
> Thanks for your consideration,
> Dave Lieberman
> David Lieberman PhD.
> Brion Technologies
> 408-653-1527

Mary X. Tang, Ph.D.
National Nanofabrication Users' Network
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA  94305
mtang at snf.stanford.edu

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