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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">For electron beam evaporation, the slower the rate the hotter the substrate will get. Also, the more power you use, gold usually requires a fair amount of power to evaporate, the hotter the substrate gets. PMMA will bubble at temps of
80C or higher. One way to prove this out is to double the rate (which decreases the exposure time in half) and see if that cures the bubble issue. There are alternate ways to run at lower powers and keep the same rate through the use of spacers under the
crucible liners. But I would for now just see if increasing the rate a bit will keep the PMMA from bubbling.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Let me know if you have further questions.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Rob<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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Learn why this is important</a> <o:p></o:p></span></p>
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<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:5.4833in;height:4.1083in" id="Picture_x0020_1" src="cid:image001.png@01DBFAF5.FA722E00"><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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