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<p class="MsoNormal">Hi Savitha,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I had the same issue with blistering on PMMA sample. You can try increasing the rate and see whether this reduce, (Ex in my case I had deposition of Ti 5A/s and Au 10 A/s).<o:p></o:p></p>
<p class="MsoNormal">You can also add spacer between the crucible and pocket, this might help in reducing the current to evaporate the metals (and hence less electrons)<o:p></o:p></p>
<p class="MsoNormal">As others have suggested we did install Ebeam optimizer to get rid of the blistering.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The beam optimizer – enhances the magnetic field (can degrade over time) so that all electrons will be captured during the 270 degree turn from the filament and then hit the pocket. If the magnetic field is off or weak higher velocity electrons
can escape the confines of the magnetic field and be driven to the substrate. The beam optimizer just added some B field to account for this.<o:p></o:p></p>
<p class="MsoNormal">Attaching the picture how the Beam optimizer looks.<o:p></o:p></p>
<p class="MsoNormal">Hope this helps.<o:p></o:p></p>
<p class="MsoNormal">Shiva<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span style="font-size:9.0pt">Shivakumar Bhaskaran, Ph.D.,
<o:p></o:p></span></b></p>
<p class="MsoNormal"><span style="font-size:9.0pt;color:black">John D. O’Brien Nanofabrication Laboratory<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;color:black">Michelson Hall, 1002 Childs Way, MCB LL121,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;color:black">Los Angeles, California 90089, 213 821 2374<o:p></o:p></span></p>
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<p class="MsoNormal"><b>From:</b> 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 3:54 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></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p><span style="font-size:12.0pt;color:black">Hello!<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;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-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">We are using a Leybold UNIVEX400 E-Beam Evaporator.<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">For a stack deposition of metals, example Cr/Au (10/50 nm)<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;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-size:12.0pt;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-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Few tool and process details:<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;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-size:12.0pt;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-size:12.0pt;color:black">Base Pressure around 2 E-06 Torr<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Deposition at room temperature<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">OPL resists used (AZ 5214E, S 1813, AZ 4562)<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">EBL resists(PMMA 950 A4, PMMA 495 A4, EL-9) <o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;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-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;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-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">With best wishes,<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Savitha<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;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-size:12.0pt;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>
<a href="http://www.cense.iisc.ac.in">www.cense.iisc.ac.in</a><o:p></o:p></span></p>
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<p class="MsoNormal"><b><i><span style="font-size:12.0pt;color:#006FC9">*Please note the change in my e-mail id*</span></i></b><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
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