Contact Metallization Design for Low-Temperature Interconnects in MEMS Integration

Thumbnail Image

Files

isbn9789526421445.pdf (4.29 MB)

URL

Journal Title

Journal ISSN

Volume Title

School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2024-12-05
Unless otherwise stated, all rights belong to the author. You may download, display and print this publication for Your own personal use. Commercial use is prohibited.

Authors

Date

2024

Department

Sähkötekniikan ja automaation laitos
Department of Electrical Engineering and Automation

Major/Subject

Mcode

Degree programme

Language

en

Pages

70 + app. 62

Series

Aalto University publication series DOCTORAL THESES, 251/2024

Abstract

Advanced electronic interconnects must meet various criteria, including low-temperature (LT) processing, miniaturization, and a stable microstructure with optimal electrical, mechanical, and thermomechanical properties. Specific application requirements, such as those for micro-electromechanical systems (MEMS) combining mechanical and electrical parts on a micrometer scale, must also be considered. Cu-Sn solid-liquid interdiffusion (SLID) interconnects show potential for utilization in MEMS integration. However, challenges persist, such as high processing temperatures and the complexity of wet chemical electroplating materials (e.g., Cu and Sn) on wafers containing fragile movable MEMS devices. Addressing these challenges involves employing LT Sn-In instead of Sn, isolating the electroplating processes to passive structures, and using a thin film contact metallization deposited via physical vapor deposition (PVD) on the device's wafer side, providing an alternative to wet chemical processes. Therefore, this thesis aimed to identify suitable contact metallizations for Cu-Sn-based SLID systems, design the metallization stack, accordingly, investigate the microstructural evolution and mechanical properties of the interconnects, assess their reliability, and demonstrate the utilization of LT-SLID, connected with TSVs, to create three-dimensional (3D) interconnects with a specific focus on 3D MEMS integration. Cobalt emerged as the most viable contact metallization option to interact with Cu-Sn-based SLID interconnects. The results showed that the microstructure of the Cu-Sn/Co bond line evolves over time at elevated temperatures or longer bonding times; hence, the Co-to-Sn thickness ratio must be controlled to prevent bond failures. No such concerns were observed with the Cu-Sn-In/Co joints. Moreover, the Cu-Sn-In/Co system exhibited promising results that met the interconnects' requirements, such as the tensile strength requirements of MIL-STD-883 method 2027.2. The bonding process was demonstrated at temperatures as low as 200 °C, resulting in a void-free stable microstructure even after a high-temperature storage (HTS) test. Furthermore, the tensile strength of the bonds improved after the HTS test. The compatibility of the developed interconnects with TSVs was confirmed, enabling the fabrication of 3D SLID-TSV interconnects for the advanced integration of MEMS devices. These interconnects demonstrate better performance than Cu-Sn SLID-TSV interconnects, which have faced challenges such as silicon cracking and void formation. This finding highlights the effectiveness of the 3D LT-interconnects.

Description

Supervising professor

Paulasto-Kröckel, Mervi, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland

Thesis advisor

Vuorinen, Vesa, Dr., Aalto University, Department of Electrical Engineering and Automation, Finland

Keywords

advanced electronics integration, 3D MEMS integration, 1st level interconnects, Cu- Sn-SLID, contact metallization, microstructure, mechanical properties, interconnects reliability, high-temperature storage, thermal shock, 3D interconnects

Other note

Parts

  • [Publication 1]: Emadi, Fahimeh, Vuorinen, Vesa, Dong, Hongqun, Ross, Glenn, & Paulasto-Kröckel, Mervi (2022). Investigation of the microstructural evolution and detachment of Co in contact with Cu–Sn electroplated silicon chips during solidliquid interdiffusion bonding. Journal of Alloys and Compounds, 890, 161852.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202110139580
    DOI: 10.1016/j.jallcom.2021.161852 View at publisher
  • [Publication 2]: Emadi, Fahimeh, Vuorinen, Vesa, Mertin, Stefan, Widell, Kim, & Paulasto-Kröckel, Mervi (2022). Microstructural and mechanical characterization of Cu/Sn SLID bonding utilizing Co as contact metallization layer. Journal of Alloys and Compounds, 929, 167228.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202210196045
    DOI: 10.1016/j.jallcom.2022.167228 View at publisher
  • [Publication 3]: Emadi, Fahimeh, Vuorinen, Vesa, Ross, Glenn, & Paulasto-Kröckel, Mervi (2023). Co, In, and Co–In alloyed Cu6Sn5 interconnects: Microstructural and mechanical characteristics. Materials Science and Engineering: A, 881, 145398.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202308114754
    DOI: 10.1016/j.msea.2023.145398 View at publisher
  • [Publication 4]: Emadi, Fahimeh, Vuorinen, Vesa, Liu, Shenyi, & Paulasto-Kröckel, Mervi (2024). Novel low-temperature interconnections for electronics integration: demonstration and reliability. IEEE Transactions on Components, Packaging and Manufacturing Technology.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202410236835
    DOI: 10.1109/TCPMT.2024.3430061 View at publisher
  • [Publication 5]: Emadi, Fahimeh, Liu, Shenyi, Vuorinen, Vesa, & Paulasto-Kröckel, Mervi (2024). Low-temperature SLID-TSV interconnects for 3D (MEMS) packaging. IEEE Transactions on Components, Packaging and Manufacturing Technology, accepted with minor revision

Citation

Permanent link to this item

https://urn.fi/URN:ISBN:978-952-64-2144-5

Collections

[diss] Sähkötekniikan korkeakoulu / ELEC