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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Hi Savitha,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Have you checked the temperature of the substrate? That’s one thing to check, but I suspect the issue is with exposure to electrons, particularly if regular lithographic resists
are performing ok.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">We saw a nearly identical issue with PMMA in our evaporator and it was solved by the installation of a permanent magnet to capture more of the electrons that are (perhaps)
straying from the gun. The difference was night and day (see images below).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Before magnet installation (100nm Ti dep on PMMA-coated wafer):<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><img width="535" height="561" id="Picture_x0020_2" src="cid:image001.png@01D4BA13.640D86A0"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">After magnet installation (100nm Ti on PMMA coated wafer):<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><img width="614" height="435" id="Picture_x0020_1" src="cid:image002.png@01D4BA13.640D86A0"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Hope this helps, and if you’ve already investigated a host of issues, this might be the only remaining one.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Norman Gottron<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Process Engineer, Carnegie Mellon University Nanofabrication Facility<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Electrical and Computer Engineering | Carnegie Mellon University<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">5000 Forbes Ave<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Pittsburgh, PA 15213<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif">Phone: 412-268-4205<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><a href="http://www.ece.cmu.edu/">www.ece.cmu.edu</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif;color:#1F497D"><a href="http://www.nanofab.ece.cmu.edu/">www.nanofab.ece.cmu.edu</a></span><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana",sans-serif"><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 [mailto:labnetwork-bounces@mtl.mit.edu]
<b>On Behalf Of </b>Savitha P<br>
<b>Sent:</b> Friday, February 01, 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>
<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-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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