<div dir="auto"><div>Hi Bernhard,</div><div dir="auto"><br></div><div dir="auto">Have you for EDX on the sample to see what it is?  Al and Silicon trade places. Si and Al difuse into each other and continue until they have completely exchanged places. I used this technique in past ti create P doped Si due to some Al staying behind in the Si. There is a possibility that if the sample  gets warm enough and the deposition takes long enough, that you are seeing Si crystals coming out. If that checks out, then increase your rate of evaporation  to limit the diffusion.</div><div dir="auto"><br></div><div dir="auto">I cannot think of other possibilities other than some sort of contamination, but that may be less likely.</div><div dir="auto"><br></div><div dir="auto">Cheers,</div><div><br></div><div data-smartmail="gmail_signature"><div dir="ltr">Carlos Gramajo<div>Cleanroom Research Scientist</div><div>Shared Equipment Authority (SEA), Rice University</div><div>Cell: 713-470-8115; Office: 713-348-8243; <a href="mailto:cg70@rice.edu" target="_blank">cg70@rice.edu</a></div></div></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Wed, Aug 20, 2025, 6:44 PM Bernhard Reineke <<a href="mailto:bernhard.reineke@uni-paderborn.de">bernhard.reineke@uni-paderborn.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">





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Dear Guoliang,<br>
<br>
Could this be electromigration?<br>
<br>
Best,<br>
Bernhard <br>
<br>
<br>
<br>
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<div id="m_-5776235496601945526divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Von:</b> labnetwork <<a href="mailto:labnetwork-bounces@mtl.mit.edu" target="_blank" rel="noreferrer">labnetwork-bounces@mtl.mit.edu</a>> im Auftrag von Wang Guoliang <<a href="mailto:guoliang.wang@silicon-austria.com" target="_blank" rel="noreferrer">guoliang.wang@silicon-austria.com</a>><br>
<b>Gesendet:</b> Mittwoch, 20. August 2025 21:31:46<br>
<b>An:</b> <a href="mailto:labnetwork@mtl.mit.edu" target="_blank" rel="noreferrer">labnetwork@mtl.mit.edu</a><br>
<b>Betreff:</b> [labnetwork] Troubleshooting defects in thick Al film (750 nm, 200 mm Si, e-beam evap)</font>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Dear All from the Labnetwork community,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Recently, our lab received a request to deposit a 750 nm aluminum film on a 200 mm Si substrate using e-beam evaporation. The deposition was carried out with an
 aluminum slug in a 40 cc water-cooled pocket. The process proceeded smoothly with stable rate, power, and pressure.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">However, upon initial microscopic inspection, the deposited aluminum film exhibited numerous black dots distributed across the entire wafer. We attempted several
 approaches to eliminate these defects, but so far have been unsuccessful.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">I am wondering if anyone has encountered similar issues when depositing thick aluminum films. Any insights or suggestions on how to address this problem would be
 greatly appreciated.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Details of the evaporation:<u></u><u></u></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Deposition rate: 1 A/s<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Deposition power: ~20%
<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Deposition pressure: ~5E-7 mbar<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Substrate cooling: No (Wafer were placed on a planar wafer holder)<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Throw distance: 1 m
<u></u><u></u></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Approaches we have already tried:<u></u><u></u></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">AFM/SEM characterization</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">
 – The black dots varied in size, with the largest reaching ~200 nm in diameter. Their morphology was pyramid-like, featuring a central peak surrounded by some trenches.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">EDX analysis</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"> – The
 black dots were identified as aluminum.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">FIB analysis
</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">– There was no cavity inside the black dots.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Adhesion layer</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"> –
 Adding a 75 nm Ti adhesion layer yielded no improvement.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Different deposition rate at 5 A/s and 0.5 A/s</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">
 – Both yielded no improvement. <u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Thickness variation</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">
 – Depositions at 200 nm, 400 nm, and 600 nm were tested. Defects only appeared in the 600 nm Al layer. All wafers exhibited similar film stress.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Pre-melted aluminum pellets</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">
 – Using a carbon crucible liner, reduced deposition power, and the same rate resulted in an increased number of black dots.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Multiple-stage deposition
</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">– Depositing 400 nm with a liner, pausing for 30 minutes, and then depositing an additional 350 nm yielded no improvement.<u></u><u></u></span></li><li class="m_-5776235496601945526MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Alternative substrates</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">
 – Depositions on Si substrates with thermal oxide and on fused silica showed no improvement.<u></u><u></u></span></li></ul>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Attached are the microscope image, AFM image, and SEM image for your reference.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Thanks and best regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Arial",sans-serif">Guoliang<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;color:#000001">Guoliang</span><span style="font-size:1.0pt;font-family:"Times New Roman",serif;color:white">​​</span><span><u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;color:#000001">Silicon Austria Labs GmbH</span><span><u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;color:#009a9b"><a href="mailto:guoliang.wang@silicon-austria.com" target="_blank" rel="noreferrer"><span style="color:#009a9b">guoliang.wang@silicon-austria.com</span></a></span><span><u></u><u></u></span></p>
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