【Device Papers】Overcoming BEOL Thermal Constraints Via Low-Temperature Cu–Cu and Cu–Oxide Bonding of α-Ga₂O₃ UV-C Photodetectors

      Researchers from Seoul National University of Science and Technology have published a dissertation titled " Overcoming BEOL Thermal Constraints Via Low-Temperature Cu–Cu and Cu–Oxide Bonding of α-Ga₂O₃ UV-C Photodetectors " in 2026 IEEE 76th Electronic Components and Technology Conference (ECTC)

Abstract

      Gallium oxide (α-Ga₂O₃) is an ultra-wide bandgap semiconductor (~5.3 eV) with intrinsic solar-blind characteristics, making it a promising material for UV-C photodetectors. However, the high crystallization temperature required for high-quality α-Ga₂O₃ (>450 °C) is fundamentally incompatible with the CMOS back-end-of-line (BEOL) thermal budget (<400 °C), significantly limiting its direct integration with CMOS platforms.In this work, we demonstrate a BEOL-compatible low-temperature bonding framework for α-Ga₂O₃ UV-C photodetectors based on thermo-compression bonding (TCB), with a particular focus on plasma-activated Cu–oxide bonding. Sub-350 °C Cu–Cu bonding is first employed as a baseline to verify that bonding-based integration can be achieved without introducing structural or electrical degradation. To further extend the thermal margin beyond conventional metallic bonding, we introduce a Cu–oxide bonding strategy motivated by thermodynamic considerations of oxide stability. Based on Ellingham-type oxide stability trends, we hypothesize that Cu2O can act as an effective interfacial bonding mediator between Cu and α-Ga₂O₃. Ar plasma treatment is applied to the α-Ga₂O₃ surface to activate oxygen vacancies, thereby enhancing interfacial reactivity and enabling oxide-mediated bonding at reduced temperatures. As a result, direct Cu–oxide bonding is achieved at temperatures below 300 °C. Cross-sectional transmission electron microscopy (TEM) reveals a continuous and well-bonded Cu–oxide interface, supporting the feasibility of the proposed bonding mechanism. This plasma-activated Cu–oxide bonding framework relaxes BEOL thermal constraints while simplifying the bonding architecture, providing a scalable pathway for heterogeneous integration of α-Ga₂O₃ and other wide-bandgap oxide semiconductors in advanced 3D-IC platforms.

DOI：

https://doi.org/10.1109/ECTC51846.2026.00373