Hi Evelyn,

Since it is very unlikely that you are growing anything during an
ashing process, the next logical conclusion is that you are *removing*
material from the areas without metal.  You did not describe your
process, but assuming that you have patterned metal on a bare
substrate or wafer, it is conceivable that you removed 80nm of
material from the unmetallized areas.  This may account for the
"growth" that you see.

BTW, are these measurements done with a profilometer?  Is it possible
that the metrology tool itself is causing the uncertainty?

Brad Cantos
[email protected]
http://holage.com

On Apr 28, 2009, at 4:05 PM, Evelyn B wrote:

> To all,
>
> I measured the average thickness of a Ti/Pt stack-up on a Si wafer at
> three different locations as summarized below:
>
>                  *  Before ashing        After ashing      Delta*
> Structure #1: 139.7 nm              219.00 nm         79.30 nm
> Structure #2: 122.5 nm              199.75 nm         77.25 nm
> Structure #3: 117.0 nm              200.00 nm         83.00 nm
>
> After doing the ashing I did not observe any damage to the Pt layer
> but
> can't explain the increase in thickness above, especially when I had
> already
> calculated an etch rate of 11 nm/min and had only etched for 3
> minutes.  The
> ashing recipe is 150 W, 44 sccm, 250 mT for 3 minutes in O2 plasma (PE
> mode).
>
> Can anyone think of anything that could cause a change of 80 nm in
> thickness?
>
> --
> EVELYN BENABE