New bonding technologies for wafer-level packaging and 3D heterointegration

As part of the Research Fab Microelectronics Germany (FMD), Leibniz IHP modernized part of its research infrastructure over the past three years. Sebastian Schulze conducts research in the field of Al-Al bonding and works in Frankfurt (Oder) on one of the new high-tech devices – a high-vacuum bonder that helps, among other things, to reduce the high temperatures during bonding and thus protects the components.

© IHP GmbH
Sebastian Schulze
© IHP GmbH
Sebastian Schulze with colleagues Patrick Krüger and Thomas Voß (f.l.t.r.) in front of the high-vacuum bonder in the IHP Nanolab.

Mr. Schulze, what are you working on right now?

I work at the Leibniz Institute for Innovative Microelectronics and I am currently involved in the optimization of physical and chemical vapor deposition processes for metal deposition and the solution of technology problems in the interconnect system. Due to FMD and the accompanying modernization of IHP’s research infrastructure, my field of work has expanded to include aluminum to aluminum (Al-Al) wafer bonding. Since 2018, I have been working on Al-Al thermocompression bonding, preparation of the required wafers and post-processing. I am also pursuing a PhD on this topic. Currently, I spend a lot of time in the lab and I am busy with process development on a new wafer bonder.

What does “wafer bonding” mean and what is it used for?

Wafer bonding is about permanently connecting two wafers and ensuring low contact resistance at the Al-Al interface. Until now, oxide formation on the Al surfaces was one of the main limitations to realize reliable electrical connections with low contact resistance. Successful bonding was only possible at a very high temperature (> 400 °C). The high vacuum bonder I am currently working on circumvents exactly this problem.

How do these new technological opportunities help you in your field of research?

A novel surface treatment based on plasma cleaning combined with processing of the wafers under ultra-high vacuum enables oxide-free Al-Al wafer bonding. As a result, the temperatures during bonding can be reduced enormously to approx. 150 °C. This protects the components and reduces thermomechanical stresses during bonding. Another special feature: optical alignment with a very high accuracy of less than 1 µm enables the production of electrically conductive Al interconnects with ultra-fine dimensions between the substrates. With the help of this new bonding technology, future-oriented possibilities arise in the area of wafer-level packaging and 3D heterointegration, in which different semiconductor technologies can be combined to obtain higher functionality and performance.

Sebastian Schulze was born in Burg in 1985, studied physical engineering at the Technical University of Wildau and graduated with an engineering diploma in 2009. He then worked at the IHP in the field of material characterization and dealt with various methods for surface analysis. After a stay abroad in 2011 in Vancouver, Canada, he returned to IHP in 2012 and his work focus shifted to process development. While working, he obtained his M.Sc. in nanotechnology from the University of Kaiserslautern in 2017. In addition to his scientific work at IHP, Sebastian Schulze is a passionate triathlete and is currently preparing for a race at the Ironman distance.