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<p style="margin-top:0;margin-bottom:0">Dear Nathan, Shivakumar, Mark, David, Mary and Norman:</p>
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<p style="margin-top:0;margin-bottom:0">Thank you so much for all your comments. We will work with all your suggestions and get back to you.</p>
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<p style="margin-top:0;margin-bottom:0">Regards,</p>
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<p style="margin-top:0;margin-bottom:0">Savitha</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nathan Nelson - Fitzpatrick <nnelsonfitzpatrick@uwaterloo.ca><br>
<b>Sent:</b> 01 February 2019 20:01:12<br>
<b>To:</b> Savitha P; labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Blistering of metal film stack on PMMA</font>
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<p class="x_MsoNormal"><span lang="EN-US">Hi Savitha,</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">I have seen and experienced this issue before. My understanding is that the PMMA is blistering due to electrons impinging on your sample, over-dosing the PMMA. When I experienced this issue on my tool I did some searching
online and found this report that correlated carbon in the Au melt to an increased current of electrons scattering off of the melt and into the sample.</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US"><a href="http://www.skyworksinc.com/downloads/press_room/published_articles/GaAs_Mantech_052010_6.pdf">http://www.skyworksinc.com/downloads/press_room/published_articles/GaAs_Mantech_052010_6.pdf</a></span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">In my case I supposed that the likely source of the carbon was from the FABMATE crucible liner our lab was using for our Gold evaporation process. The liner’s glassy finish appeared to be wearing down due to handling
and was likely leaving a small amount of carbon dust on the melt every time it was added or removed from our evaporator. </span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">I was able to fix our issue by taking the gold melt out of our old FABMATE liner, cleaning the carbon dust off of the ingot with some IPA and putting it back in a new FABMATE liner. Once the ingot was cleaned and put
into a new liner the surface of the melt looked appreciably different. When contaminated with carbon it appeared to have a “skin” on the top of the melt, while the clean melt has a uniform “liquid-like” appearance.
</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">FYI: I have recently moved on to a Molybdenum liner as described in this Materion report, the downside with this is that the Gold wets the liner surface and will likely be difficult to reclaim if/when I have to do
so.</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US"><a href="https://materion.com/-/media/files/advanced-materials-group/me/technicalpapers/developingafundamentalunderstandingofgoldspitting.pdf?la=en&hash=502E7BF53ECF2EE5923F4B5F7488A78B3B2ED05F">https://materion.com/-/media/files/advanced-materials-group/me/technicalpapers/developingafundamentalunderstandingofgoldspitting.pdf?la=en&hash=502E7BF53ECF2EE5923F4B5F7488A78B3B2ED05F</a></span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">Feel free to reach out if you want to discuss this problem further.</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
<p class="x_MsoNormal"><span lang="EN-US">Best regards,</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> -Nathan</span></p>
<p class="x_MsoNormal"><span lang="EN-US"> </span></p>
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<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">Nathan Nelson-Fitzpatrick PhD</span></p>
<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">Nanofabrication Process & Characterization Engineering Manager</span></p>
<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">Quantum-Nano Fabrication and Characterization Facility (QNFCF)</span></p>
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<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">University of Waterloo</span></p>
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<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">P: 519-888-4567 ext. 31796</span></p>
<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black">C: 226-218-3206</span></p>
<p class="x_MsoNormal"><span style="font-family:"Verdana",sans-serif; color:black"><a href="https://fab.qnc.uwaterloo.ca"><span style="color:#0563C1">https://fab.qnc.uwaterloo.ca</span></a></span></p>
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<p class="x_MsoNormal"><b><span style="font-size:12.0pt; color:black">From: </span>
</b><span style="font-size:12.0pt; color:black"><labnetwork-bounces@mtl.mit.edu> on behalf of Savitha P <savithap@iisc.ac.in><br>
<b>Date: </b>Friday, February 1, 2019 at 8:58 AM<br>
<b>To: </b>"labnetwork@mtl.mit.edu" <labnetwork@mtl.mit.edu><br>
<b>Subject: </b>[labnetwork] Blistering of metal film stack on PMMA</span></p>
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<p><span style="font-size:12.0pt; color:black">Hello!</span></p>
<p><span style="font-size:12.0pt; color:black"> </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.</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">We are using a Leybold UNIVEX400 E-Beam Evaporator.</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">For a stack deposition of metals, example Cr/Au (10/50 nm)</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.</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.</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Few tool and process details:</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.</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</span></p>
<p><span style="font-size:12.0pt; color:black">Base Pressure around 2 E-06 Torr</span></p>
<p><span style="font-size:12.0pt; color:black">Deposition at room temperature</span></p>
<p><span style="font-size:12.0pt; color:black">OPL resists used (AZ 5214E, S 1813, AZ 4562)</span></p>
<p><span style="font-size:12.0pt; color:black">EBL resists(PMMA 950 A4, PMMA 495 A4, EL-9) </span></p>
<p><span style="font-size:12.0pt; color:black"> </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.</span></p>
<p><span style="font-size:12.0pt; color:black"> </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.</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">With best wishes,</span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black">Savitha</span></p>
<p class="x_MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
<p><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="x_MsoNormal"><span style="font-size:12.0pt; color:black">Dr. Savitha P<br>
Chief Operating Officer</span></p>
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<p class="x_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>
www.cense.iisc.ac.in</span></p>
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<p class="x_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"></span></p>
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