Michael,

This DRIE doesnt have DC bias but a RF bias, so metal exposure is allowed.
However, I am interested in finding a solution with photoresist as a mask.
I used thermal grease and it resulted in localized heating effects which
caused the PR to be eaten away quickly, in those places. Can you tell me if
200u+ deep etches have been attempted with the PR as adhesive technique.
Also, do you have some information on how the cooling affects the sidewall
angle?

Thanks
Shree



On Thu, Dec 6, 2012 at 11:17 AM, Michael Martin <
[email protected]> wrote:

> Hi Shree,
>    First, a lot of fab's do not like for metal (as is on your handle wafer)
> to be exposed to the plasma of the DRIE.  The metal will sputter, redeposit
> on your etched structures (and the ceramic inside the DRIE) and cause
> micromasking.  This can lead to grass formation in your etched area.
>   We have used silver loaded thermal grease in the past but have also had a
> problem removing it after etching; particularly after etching completely
> through a wafer.  We routinely use a thick resist (SPR 220, 5-7um) on the
> back of the etch wafer and a layer of thinner resist (1827) on the handle
> wafer.  Then to release after the etch just soak both of them in acetone.
> Of course having a thick resist on the back will lower the thermal
> conductivity and may have some deleterious effects on side wall angle if
> you are etching deep, high aspect ratio features.
>
> Cheers,
>    Michael
>
>
>
> On Wed, Dec 5, 2012 at 3:24 PM, Tinka Li  wrote:
>
> > Hi Shree,
> >
> > You meant something like Fomblin oil? 1 or 2 drops on your carrier,
> > smear out nicely, would do the chucking perfectly. Can also easily
> > remove (slide) your wafer out of your carrier wafer after DRIE. BUT, you
> > may have a little trouble in cleaning our wafer afterwards.
> >
> > Prime Wafers
> > Rotterdam, NL
> >
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On Behalf Of
> > Shree Narayanan
> > Sent: Wednesday, December 05, 2012 4:36 PM
> > To: General MEMS discussion
> > Subject: [mems-talk] Adhesive to bond onto a carrier wafer for etching
> >
> > Hello all,
> >
> > I need to mount a 4" silicon wafer on a 6" metallized carrier wafer, in
> > order to etch it in a Alcatel deep-reactive ion etcher. I am wondering
> > if
> > someone has used thermal vacuum grease for this purpose that can be
> > removed
> > easily at the end. The silicon wafer is patterned with photoresist and
> > has
> > no other material on it.
> >
> > Thanks
> > Shree
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