STS shower head thru etch effect

Jim McVittie mcvittie at snf.stanford.edu
Tue Jul 5 12:48:42 PDT 2005


Chris,

Our charging results were similar to tilt shown in your SEM.
In Fig 3 of the APL paper I referenced, we show a profile tilt which varied from
30 to 5 degree as a function of distance from an open area when using a resist
mask. The 5 degree tilt occurred at about 220 um from the opening while the 30
degree tilt occurred near the opening. For the same process and pattern, we got
no tilt when we used a Cr mask. The same paper shows ion trajectory simulations
for different surface charging potentials. At a potential of 55V, the simulated
incident angle of the ion trajectories as a function of distance from the open
area agreed very closely with the measure profile tilts.  From a charging
viewpoint, the Al ring in the holder could behave similar to the open areas in
our work. In our simulations, we assumed the open exposed Si areas were grounded
while the resist surface was charged.  In later work, we actually measured
surface charging voltages, which agreed with our simulations.

    Jim

,  the charging work I referenced, we  same behavior

Chris Kenney wrote:

> Sorry to over load all the STS users' mailboxes, but I've
> attached an image of the tilt we observed. To set the scale
> this is a 525 micron thick wafer and this image was
> taken near the wafer's edge. As you can see the tilt angle
> varied strongly with distance from the edge.
>
> On Tue, 5 Jul 2005, Chris Kenney wrote:
>
> > We also observed a shower-head effect several years ago on STS1
> > and we thought it might be associated with use of the aluminum holder.
> >
> > Although we don't generally look for them, we haven't noticed tilted
> > features before or since.
> >
> > Thanks for providing the references.
> >
> > Chris
> >
> > On Tue, 5 Jul 2005, Jim McVittie wrote:
> >
> > > Jaime,
> > >
> > > It sounds like you are seeing a charging effect. Back in the early 90's,
> > > I did a bit of work on etch profile distortion due charging. We did
> > > etching experiments, direct charging measurements and simulations. See
> > > papers below. The work was done on one of the Dryteks for trenches
> > > etched in the range of 5 to 10 deep. In general, charging is due to
> > > plasma non-uniformity although the pattern on your wafer can have a
> > > strong effect. In the Drytek case we used a  magnet  to cause plasma
> > > non-uniformity. You are the first user to ever report this effect on
> > > STS-1 so I suspect a temporary hardware problem could be the cause.  Can
> > > you give me more details on what you are seeing, such as how the tilt
> > > varies across the wafer. Also are you seeing a lot of etch rate
> > > non-uniformity.
> > >
> > >     Jim
> > >
> > > S. Murakawa and J.P. McVittie,  "Ion Trajectory Distortion and Profile
> > > Tilt by Surface Charging in Plasma Etching", Appl. Phys. Letts., vol.
> > > 64(12), pp.1558-1560, Mar., 1994.
> > >
> > > S. Murakawa and J.P. McVittie, "Direct Measurement Of Surface Charging
> > > Potential In Plasma Etching", Proceedings 2nd  Intnl. Conf. Reactive
> > > Plasmas, pp. 747-750, Jan. 1994, Yokohama, Japan, also in Jpn. J. Appl.
> > > Phys., Vol. 33, pp. 4446-4449, Part 1, July 1994.
> > >
> > > S. Murakawa and J.P. McVittie, "Mechanism of Surface Charging Effects on
> > > Etching Profile Defects", Proceedings of Symp. on Dry Process ( IEE
> > > Japan), pp. 39-44, Nov. 1993, Tokyo, Japan, also  in Jpn. J. Appl.
> > > Phys., Vol.33, pp.2184-2188, 1994.
> > >
> > >
> > > jgarate at invensense.com wrote:
> > >
> > > >    Part 1.1    Type: Plain Text (text/plain)
> > > >            Encoding: 8bit
> > >
> > >
> >
>
>   ------------------------------------------------------------------------
>                                Name: tiltvariation.jpg
>    tiltvariation.jpg           Type: JPEG Image (image/jpeg)
>                            Encoding: BASE64
>                     Download Status: Not downloaded with message




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