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<p class="MsoNormal">Hi Philipp:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Two papers of interest that may help explain:<o:p></o:p></p>
<p class="MsoNormal"><a href="https://pubs.aip.org/avs/jvb/article/39/5/052601/1070034/Role-of-electron-and-ion-irradiation-in-a-reliable">https://pubs.aip.org/avs/jvb/article/39/5/052601/1070034/Role-of-electron-and-ion-irradiation-in-a-reliable</a><o:p></o:p></p>
<p class="MsoNormal"><a href="https://iopscience.iop.org/article/10.1088/1361-6463/abe89b">https://iopscience.iop.org/article/10.1088/1361-6463/abe89b</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">An insightful experiment, inspired by Sun’s paper, to have a plain wafer with PMMA spend time in the evaporator, with the power level just below the point where you get deposition. Maybe 15-30 mins is sufficient. That will expose your
sample to all the things you don’t want (temperature, electrons, …) without putting down a film. After that treatment, develop the PMMA (assuming there was no deposition) and you may find some interesting patterns that may suggest electron exposure. See attached
image of a simple experiment we ran a few years ago (these were quick qualitative tests only). Using a shim under the crucible helped fix things for our users (less cooling = less current = less electron radiation).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">-Jorg<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></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 <labnetwork-bounces@mtl.mit.edu>
<b>On Behalf Of </b>Philipp Altpeter<br>
<b>Sent:</b> Tuesday, July 22, 2025 4:23 AM<br>
<b>To:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> [labnetwork] Bubble formation when e-beam evaporating Gold on PMMA<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>Dear all,<o:p></o:p></p>
<p>In recent months, we installed a new UHV e-beam evaporator and have since encountered significant issues with our standard lift-off process using 3<span style="font-family:"Arial",sans-serif"> </span>nm Chromium followed by 50<span style="font-family:"Arial",sans-serif"> </span>nm
Gold. Specifically, we are observing the formation of large bubbles beneath the PMMA, which severely damage the PMMA layer (see image below). The rate is decently low, 0.6 A/s at around 40mA emission current, 10 kV. After around 30 nm of thickness, bubbles
become clearly visible.<o:p></o:p></p>
<p>Interestingly, deposition on bare silicon, silicon dioxide, or other (photo)resists appears to proceed without problems.<o:p></o:p></p>
<p>We have already tried adjusting various parameters — including cooling conditions, beam wobbling, throw distance, and acceleration voltage. We also modified the PMMA baking protocol and tested PMMA dissolved in different solvents — all without success.<o:p></o:p></p>
<p>If anyone has experienced similar issues or has suggestions for troubleshooting, your input would be greatly appreciated.<o:p></o:p></p>
<p>Thank you in advance for your help!<o:p></o:p></p>
<p>Best regards,<br>
Philipp<o:p></o:p></p>
<p><o:p> </o:p></p>
<p><img border="0" width="526" height="394" style="width:5.4791in;height:4.1041in" id="Picture_x0020_1" src="cid:image001.png@01DBFB3B.43EE8930"><o:p></o:p></p>
<pre>-- <o:p></o:p></pre>
<pre>Philipp Altpeter<o:p></o:p></pre>
<pre>Fakultät für Physik der LMU<o:p></o:p></pre>
<pre>LS Prof. Efetov<o:p></o:p></pre>
<pre>Geschwister-Scholl-Platz 1<o:p></o:p></pre>
<pre>D-80539 München<o:p></o:p></pre>
<pre>T. +49 (0)89 2180-3733<o:p></o:p></pre>
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