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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Hi Savitha,<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">As others have mentioned, this is mainly caused by electron damage to the PMMA. Here is another paper that addresses the issue with an interesting solution:
<a href="https://csmantech.org/OldSite/Digests/1999/PDF/54.pdf">https://csmantech.org/OldSite/Digests/1999/PDF/54.pdf</a>.<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">Depending on how your chamber is set up, I have one other suggestion that has not been mentioned yet. In our evaporator, we have a short throw distance and a
shutter only near the sample, not at the crucible. We found that damage was occurring before the shutter was even opened. Electron scattering from solid metal is much more than from liquid, so we believe that the flux of scattered electrons during the initial
melt steps was high enough that electrons would go around the shutter and still damage the sample. We put a metal shielding ring in place around the samples to prevent this (shown in the attached pictures), and you can see the difference between samples inside
and outside of the shield.<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">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">David<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:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> labnetwork-bounces@mtl.mit.edu <labnetwork-bounces@mtl.mit.edu>
<b>On Behalf Of </b>Savitha P<br>
<b>Sent:</b> Friday, February 1, 2019 6:54 AM<br>
<b>To:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> [labnetwork] Blistering of metal film stack on PMMA<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p><span style="font-family:"Calibri",sans-serif;color:black">Hello!<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">We need inputs deposition of metal film stack on PMMA coated substrates. We see blisters on the PMMA which creates problems during lifting off process.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">We are using a Leybold UNIVEX400 E-Beam Evaporator.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">For a stack deposition of metals, example Cr/Au (10/50 nm)<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">the film on Si and SiO2 substrate is smooth with good resistivity value.The film deposited on optical lithography patterned samples also give good lift off and the appearance of metal film on resist
is smooth and usual.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Whereas, for a film stack deposition on e-beam lithography patterned samples, the metal on the PMMA resist becomes completely blistered. The lift off is not clean, leaving behind random patches of
metal over resist on the substrate even after longer duration in solvents.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Few tool and process details:<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Source to substrate distance- Minimum 20 cm and Maximum 35 cms. Blisters observed for both the distances.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Deposition rates of Cr 0.3 nm/s and Au 0.3 nm/s<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Base Pressure around 2 E-06 Torr<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Deposition at room temperature<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">OPL resists used (AZ 5214E, S 1813, AZ 4562)<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">EBL resists(PMMA 950 A4, PMMA 495 A4, EL-9) <o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">We have already tried different baking times for PMMA, different deposition rates, wait times between depositions and also grounding the substrate.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Please let us know if anyone has an idea on how to solve this.<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">With best wishes,<o:p></o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black">Savitha<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
<p><span style="font-family:"Calibri",sans-serif;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:black">Dr. Savitha P<br>
Chief Operating Officer<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;color:black">National Nanofabrication Centre<br>
Centre for Nanoscience and Engineering<br>
Indian Institute of Science<br>
Bangalore - 560012<br>
India.<br>
Ph. +91 80 2293 3319<br>
</span><a href="http://www.cense.iisc.ac.in"><span style="font-family:"Calibri",sans-serif">www.cense.iisc.ac.in</span></a><span style="font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><b><i><span style="font-family:"Calibri",sans-serif;color:#006FC9">*Please note the change in my e-mail id*</span></i></b><span style="font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
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