<div dir="ltr"><div dir="ltr">Hi Guoliang,<br><br>To me it sounds a lot like classic Al hillock formation from stress relief in thick films. As the Al film grows thicker, compressive stress builds due to differential thermal expansion between the Al and Si. Without active substrate cooling there is localized heating that gives the Al atoms enough mobility to relieve stress by extruding outwards.</div><div dir="ltr"><br>If you have any active cooling capabilities that would likely help. If not, you could also try breaking the deposition into more steps with cooldowns, or even tossing in a thin Ti layer mid-stack. Here is a reference that might be worth checking out.</div><div dir="ltr"><br></div><div dir="ltr">Ericson, Fredric, et al. "A transmission electron microscopy study of hillocks in thin aluminum films." Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 9.1 (1991): 58-63.</div><div dir="ltr"><br></div><div dir="ltr">Best,</div><div dir="ltr">Jacob<br><div><div dir="ltr" class="gmail_signature"><div dir="ltr">-------------------------------------<br><b>Jacob Trevino, PhD</b><br>Senior Director, Columbia Nano Initiative Labs<br>Columbia University<br>530 W120th Street, Room 1015/MC 8903<div>New York, NY 10027<br>Email:<a href="mailto:jt2900@columbia.edu" target="_blank"> jt2900@columbia.edu</a><br>Cell: 734-787-2171</div><div>Desk: 212-854-9927<br><div><a href="https://cni.columbia.edu/" target="_blank">https://cni.columbia.edu/</a></div></div><div><a href="https://www.linkedin.com/in/jacob-t-trevino/" target="_blank">https://www.linkedin.com/in/jacob-t-trevino/</a></div></div></div></div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Wed, Aug 20, 2025 at 3:50 PM Wang Guoliang <<a href="mailto:guoliang.wang@silicon-austria.com">guoliang.wang@silicon-austria.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg5157712564160871053">
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Dear All from the Labnetwork community, 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. </div>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Deposition rate: 1 A/s<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Deposition power: ~20%
<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Deposition pressure: ~5E-7 mbar<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">AFM/SEM characterization</span></b><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">EDX analysis</span></b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif"> – The
black dots were identified as aluminum.<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">FIB analysis
</span></b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">– There was no cavity inside the black dots.<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Adhesion layer</span></b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif"> –
Adding a 75 nm Ti adhesion layer yielded no improvement.<u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif">
– Both yielded no improvement. <u></u><u></u></span></li><li class="m_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Thickness variation</span></b><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Pre-melted aluminum pellets</span></b><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Multiple-stage deposition
</span></b><span lang="EN-US" style="font-size:11pt;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_5157712564160871053MsoListParagraph" style="margin-left:0cm"><b><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Alternative substrates</span></b><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;font-family:Arial,sans-serif">Attached are the microscope image, AFM image, and SEM image for your reference.<u></u><u></u></span></p>
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<p class="MsoNormal"><span lang="EN-US" style="font-size:11pt;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:11pt;font-family:Arial,sans-serif">Guoliang<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Arial,sans-serif"><u></u> <u></u></span></p>
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