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<p class=MsoNormal><span style='color:#1F497D'>Fluorine poisoning is really the
culprit here. In the email I read, they used the RIE tool <u>for nitride
etch and then ran a resist strip process</u>. Nitride etch will usually
have F based gases. F based chemistries and O2 based chemistries (for
resist strip) can not mix in the same chamber. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Here are 2 real experience I
had:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>LAM<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>An early Lam tool, the
Rainbow 4400 was released for poly, Wsi, nitride and W plug etch
processes. However, we found that when mixing etch applications in the
same chamber the oxide etch rates exponentially increase. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-F based etch step then
HBr/O2 over etch step always showed 20 to 1 selectivity of
polysilicon to oxide<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-Cl2 based etch step then
an HBr/O2 over etch step showed 100: 1 selectivity of polysilicon to oxide<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>We also battled mixed chemistry
issues in the early days at TSMC and Chartered. The early
versions of these foundries would only buy a few etch tools and then use
multiple processes in the same chamber. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-Poly etch was usually, Cl2+He
in the main etch and HBr/O2 in the over etch. HBr/O2 had a 100:1
selectivity of Poly to oxide and will only etch oxide for around 5 Angstroms
per minute. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-Nitride etch was usually SF6 or
CF4 or C2F6 based plasma<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>-W plug process was usually SF6
based plasma<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>If we had to use F in the same
chamber as a poly etch tool,( as in the native oxide punch through step at the
beginning of any poly etch), we will only use F sources very
small flows and for 10 seconds or less. Then , we will follow it
with a pump/purge step within the process run so we immediately flush any F out
of the chamber.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>If we did have F poisoning, we
found that in addition to doing a complete chamber wet clean, we
also needed to remove all parts that were not hard anodized aluminum, wet clean
these, air dry, then bake in the oven for 45 minutes. After that, we needed to
season the chamber using an O2 only process.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Obviously, this process was not
production worthy so we ended up dedicating chambers to specific
chemistries only and never had the issue again. Later on, Lam
released 2 additional tools…the 4420 which is for silicides and the 4700 which
is for plugs and trenches. This ensured that we did not mix chemistries
anymore.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>In fact, if we found that
any customer ran a F chemistry on another chamber that would require high
selectivity to oxide and then call us to escalate the issue due to oxide punch
through, we would void the warranty for a few months and not support the tool.
<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>However, if they had some F
poisoning due to back streaming Fomblin, this is easy to check and we will
support the tool. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>All you need to do is disconnect
the last segment of pump foreline closest to the chamber. If you can wipe a
colorless, oily substance, then or small, white, sticky gunk, your oil
backstreamed into the chamber.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Mattson<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The Mattson tools dry strip
tools had the same problem with F. The Mattson tools, however are NOT RIE
tools, they are downstream ICP plasma tools. An O2 only process was
the POR for resist for those tools. Each time we switched the
applications lab tools to CF4 + O2 chemistry to strip post implant resist, we
poisoned the chamber after <u>just 2 wafer runs</u>. That process
was even predominantly O2. (Flow was 3000 sccm O2 + 10 sccm CF4) We
just needed a little fluorine to punch through the cross linked layer of the
photoresist that was hardened by the implant process. After running just
2 wafer runs and then switch to a pure O2 process, we were surprised that
we literally punched through the 500 Angstroms of oxide underlayer.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>We only had 2 apps lab test
tools during Mattson’s early days so we did not have the luxury of dedicating
chambers. We would constantly change the configuration of those
tools and prep them every night if these tools had to switch chemistries (F
chemistries vs O2 only).<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>After a F poisoning (usually
done on purpose in our applications lab, so we can strip post implant resist) ,
we used to open the chambers, wet clean / wipe with isopropyl alcohol and
acetone mix. We also remove anything that is not hard anodized aluminum,
wet clean these parts, air dry and bake them in the oven. Then, we would
run 6 hours of O2 and Nitrogen plasma cleans, as an added chamber conditioning
step.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>As we increased the number of
application lab tools, we also dedicated chemistries to specific tools and
never had to go through those long nights in between experiments anymore due to
F poisoning.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Lastly, if the STS tool is the
only tool to do these experiments in a university research atmosphere, this
tool will need to run a lot of O2 only processes for conditioning, before any
resist strip experiments can be done. or <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Do chamber wipe downs (at the
very minimum) + a quick O2 plasma clean before switching to a resist strip
process.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I hope this helps. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='color:teal'>Ciel Villawatkins</span></b><b><span style='color:#002060'> </span></b><span
style='color:#002060'>| Sr. Technical Staff<br>
Abbie Gregg, Inc. | 1130 East University Drive, Suite 105, Tempe, AZ 85281<br>
</span><b><span style='color:teal'>Main</span></b><b><span style='color:#002060'>
</span></b><span style='color:#002060'>480-446-8000 | </span><b><span
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</span><b><span style='font-family:"Arial","sans-serif"'>+971(0)56
772 9531</span></b><span style='color:#002060'> </span><span
style='color:#1F497D'><o:p></o:p></span></p>
<p class=MsoNormal><b><span style='color:teal'>Email</span></b><span
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<div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Arial","sans-serif";
color:#1F497D'>Abbie Gregg</span><span style='font-size:11.0pt;font-family:
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Arial","sans-serif";
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Arial","sans-serif";
color:#1F497D'>Abbie Gregg, Inc.</span><span style='font-size:11.0pt;
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</div>
<p class=MsoNormal><span style='font-family:"Arial","sans-serif";color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:
"Tahoma","sans-serif";color:windowtext'> labnetwork-bounces@mtl.mit.edu
[mailto:labnetwork-bounces@mtl.mit.edu] <b>On Behalf Of </b>Morrison, Richard
H., Jr.<br>
<b>Sent:</b> Friday, July 29, 2011 7:47 AM<br>
<b>To:</b> Mac Hathaway; Mary Tang<br>
<b>Cc:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Need RIE help<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Well that is great info,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Here are my results so far, thanks to all whom have wrote
replies:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Removed the Teflon ring and the F peak on the plasma scope
reduced by about 30%, the ring shows heavy etch damage, according to STS it is
needed in the system to help confine the plasma<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>We found out that the “o”-ring that seals the chamber cover is
greased with fomblin grease, changing that out today, data to come.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>We will swap out the dry pump for a new one to see if we have an
oil back-stream issue due to a bad seal. One stage on the dry pump uses Fomblin
oil.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>All of you have suggested very long O2 cleans so we are going to
try that after the grease and pump change. We are also going to increase the O2
flow to 125sccm from 50sccm, increase the pressure to 250mT and increase the
power.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Any more ideas out there?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Rick<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:
"Tahoma","sans-serif";color:windowtext'> Mac Hathaway
[mailto:Hathaway@cns.fas.harvard.edu] <br>
<b>Sent:</b> Friday, July 29, 2011 9:45 AM<br>
<b>To:</b> Mary Tang<br>
<b>Cc:</b> Morrison, Richard H., Jr.; labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Need RIE help<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Hey all,<br>
<br>
This is Mac, at Harvard CNS. Our STS has shown some symptoms of this due
to polymer on the walls coming off in the O2 clean, introducing fluorine via
that route.<br>
<br>
When you wrote "the F peak is clipped of in height during the O2 plasma
clean?" Did you mean it was still there, but shorter? This
would clearly indicate the F is still there, and the only question is where
it's coming from.<br>
<br>
Perhaps a longer chamber clean, with a low-pressure step to spread out the
cleaning plasma, before the stripping runs?...<br>
<br>
Keep in mind that an O2 resist strip can gum up your chamber, and cause
instability in your regular etch processes if you're not careful.<br>
<br>
<br>
Mac<br>
<br>
Mary Tang wrote: <o:p></o:p></p>
<p class=MsoNormal style='margin-bottom:12.0pt'>Hi Richard --<br>
<br>
A similar problem was observed and diagnosed on one of our O2 ashers by one of
our industrial labmembers who was a plasma etch engineer at HP. The cause
seems to have been trace amounts Fomblin pump fluid coming back into the chamber
-- Fomblin is basically a polymerized freon, so there's your fluorine source.<br>
<br>
Mary<br>
<br>
<br>
<o:p></o:p></p>
<pre>-- <o:p></o:p></pre><pre>Mary X. Tang, Ph.D.<o:p></o:p></pre><pre>Stanford Nanofabrication Facility<o:p></o:p></pre><pre>Paul G. Allen Room 136, Mail Code 4070<o:p></o:p></pre><pre>Stanford, CA 94305<o:p></o:p></pre><pre>(650)723-9980<o:p></o:p></pre><pre><a
href="mailto:mtang@stanford.edu">mtang@stanford.edu</a><o:p></o:p></pre><pre><a
href="http://snf.stanford.edu">http://snf.stanford.edu</a><o:p></o:p></pre>
<p class=MsoNormal><br>
<br>
On 7/27/2011 4:58 AM, Morrison, Richard H., Jr. wrote: <o:p></o:p></p>
<div>
<p>Hi Everyone, <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Our facility uses an STS RIE tool (100mm wafers), to etch Nitrides/Oxides/Ti
and resist cleans. I have a big problem when we use O2 to clean off resist from
wafers. It seems that just running O2 plasma we etch 1000A/min of SiO2. It
should be impossible to etch SiO2 with O2 plasma. <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>In trouble shooting we have done the following, change the Teflon wafer
holder, disconnected the SF6, CF4 and CHF3 tanks and capped the lines, then
pumped the machine down and just ran O2 and we still etched the SiO2 at
1000A/min. We have a plasma scope and the F peak is clipped of in height during
the O2 plasma clean? <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Does anybody have any ideas on what may be going on. <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Thanks in advance, <o:p></o:p></p>
<p>Rick <o:p></o:p></p>
<p> <o:p></o:p></p>
<p> <o:p></o:p></p>
<p> <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>Rick Morrison <o:p></o:p></p>
<p>Senior Member Technical Staff <o:p></o:p></p>
<p>Acting Group Leader Mems Fabrication <o:p></o:p></p>
<p>Draper Laboratory <o:p></o:p></p>
<p>555 Technology Square <o:p></o:p></p>
<p>Cambridge, MA 02139 <o:p></o:p></p>
<p> <o:p></o:p></p>
<p>617-258-3420 <o:p></o:p></p>
<p> <o:p></o:p></p>
</div>
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