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Hello,<br>
CF4/O2 ratio is too high, I think.<br>
I suggest to do a run without O2 first, just to check it.<br>
Then try it with no more than 1-2% O2; however I see you are using
very very low flow rate for O2<br>
and making it even low you might reach the MFC accuracy limits. I
suggest to increase accordingly<br>
the CF4 flow rate to allow 1-2% O2 flow, and try to maintain the
pressure value.<br>
<br>
Some comments and suggestions:<br>
The CF4 plasma etch was the first one used to etch SiO2, Si3N4 and
Si more than 40 years ago.<br>
The German LFE barrel reactor machine was one of them.<br>
The main problem was its selectivity to Si, which was solved by
adding H2 and He for safety reasons.<br>
Then was the etch rate which was not stable; it was discovered
that the O2 desorbed from the Quartz walls<br>
was the culprit. The chamber process history counted.<br>
Then it has been established that adding ~ 1-2% of Oxygen
increases the etch rate and makes it<br>
repeatable, while adding more than 3% quenches the the etch rate.
<br>
Practically an even higher etch rate was observed by using
industrial O2 from a tank, which adds <br>
more impurities!<br>
The scientific explanation was based on the so named " Second
Order Atomic Collision" phenomena.<br>
The main etching specie is CF3- molecular ion.<br>
Its plasma concentration is increased by adding some Oxygen which
enhances its ionization rate, by<br>
the second order atomic collision. The O2 is brought by RF plasma
in a long lifetime metastable <br>
energy state higher than the CF4 ionization energy; by inelastic
collision O2 transfer this extra energy<br>
to CF4 and increases its ionization rate.<br>
The low O2 concentration acts like a ionization catalyzer. More O2
is an inhibitor.<br>
There are old papers in the Journal of Physical Chemistry around
1973, etc.<br>
Thanks, Bernard<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
On 3/7/17 1:14 PM, Jugessur, Aju S wrote:<br>
</div>
<blockquote cite="mid:D4E4526B.C880%25aju-jugessur@uiowa.edu"
type="cite">
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<div>Hi,</div>
<div><br>
</div>
<div>I have a user who is using the following Si etch recipe on
our Oxford NGP80 etcher:</div>
<div><br>
</div>
<div>RF power: 100 W</div>
<div>Pressure: 100 mT</div>
<div>CF4 flow rate: 25 sccm</div>
<div>O2 flow rate: 3.1 sccm</div>
<div><br>
</div>
<div>The etch rate from the above parameters is ~ 0.15
microns/min.</div>
<div>The selectivity is 1:3.</div>
<div> Can anyone suggest what parameters to tweak to increase the
etch rate without causing too much substrate damage or
roughness?</div>
<div><br>
</div>
<div>Thanks for your suggestions.</div>
<div><br>
</div>
<div>Regards</div>
<div>Aju</div>
<div><br>
</div>
<div>
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<font class="Apple-style-span" size="2" face="Georgia"
color="#103ffb">Aju Jugessur <i>Ph.D.</i><br>
Director, University of Iowa Microfabrication Facility<br>
</font></div>
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<font class="Apple-style-span" size="2" face="Georgia"
color="#103ffb">Professor (Adj.), Physics and Astronomy<br>
OSTC, Iowa Advanced Technology Labs<br>
University of Iowa</font></div>
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<font class="Apple-style-span" size="2" face="Georgia"
color="#103ffb">205 N. Madison St</font></div>
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<font class="Apple-style-span" size="2" face="Georgia"
color="#103ffb">Iowa City, IA 52242<br>
319 -353-2342 <br>
<a class="moz-txt-link-abbreviated" href="mailto:aju-jugessur@uiowa.edu">aju-jugessur@uiowa.edu</a><br>
<a class="moz-txt-link-freetext" href="http://ostc.uiowa.edu/uimf">http://ostc.uiowa.edu/uimf</a></font></div>
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