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.
Translated title of the contribution | Contact Metallization Design for Low-Temperature Interconnects in MEMS Integration |
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Original language | English |
Qualification | Doctor's degree |
Awarding Institution |
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Print ISBNs | 978-952-64-2143-8 |
Electronic ISBNs | 978-952-64-2144-5 |
Publication status | Published - 2024 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- advanced electronics integration
- 3D MEMS integration
- 1st level interconnects
- Cu- Sn-SLID
- contact metallization
- microstructure
- mechanical properties
- intercon- nects reliability
- high-temperature storage
- thermal shock
- 3D interconnects