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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt;font-family:"Calibri",sans-serif;color:#1F497D">That’s a good call by Bernard actually, just looking at your numbers again you are already working over 12% which is rather high for a CF4 process.
<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"> labnetwork-bounces@mtl.mit.edu
[mailto:labnetwork-bounces@mtl.mit.edu] <b>On Behalf Of </b>Bernard Alamariu<br>
<b>Sent:</b> 08 March 2017 13:39<br>
<b>To:</b> Jugessur, Aju S <aju-jugessur@uiowa.edu>; labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Si RIE etch<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><br>
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:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Hi,<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">I have a user who is using the following Si etch recipe on our Oxford NGP80 etcher:<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">RF power: 100 W<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Pressure: 100 mT<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">CF4 flow rate: 25 sccm<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">O2 flow rate: 3.1 sccm<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">The etch rate from the above parameters is ~ 0.15 microns/min.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">The selectivity is 1:3.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"> Can anyone suggest what parameters to tweak to increase the etch rate without causing too much substrate damage or roughness?<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Thanks for your suggestions.<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Regards<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US">Aju<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Georgia",serif;color:#103FFB">Aju Jugessur <i>Ph.D.</i><br>
Director, University of Iowa Microfabrication Facility</span><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Georgia",serif;color:#103FFB">Professor (Adj.), Physics and Astronomy<br>
OSTC, Iowa Advanced Technology Labs<br>
University of Iowa</span><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Georgia",serif;color:#103FFB">205 N. Madison St</span><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:10.0pt;font-family:"Georgia",serif;color:#103FFB">Iowa City, IA 52242<br>
319 -353-2342 <br>
<a href="mailto:aju-jugessur@uiowa.edu">aju-jugessur@uiowa.edu</a><br>
<a href="http://ostc.uiowa.edu/uimf">http://ostc.uiowa.edu/uimf</a></span><span lang="EN-US" style="font-size:9.0pt;font-family:"Helvetica",sans-serif"><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><br>
<br>
<br>
<o:p></o:p></span></p>
<pre><span lang="EN-US">_______________________________________________<o:p></o:p></span></pre>
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