TRANSLATION - FOR REFERENCE ONLY -
June 2, 2025
KOKUSAI ELECTRIC CORPORATION (President and CEO: Kazunori Tsukada, Head Office: Chiyoda-ku, Tokyo, Japan) is pleased to announce that, through joint research with the team led by Associate Professor Fumihiro Inoue, Director of the Research Center for Heterogeneous Integration and Associate Professor of the Semiconductor and Quantum Integrated Electronics Research Center, Institute for Multidisciplinary Sciences, YOKOHAMA National University, it has successfully deposited a novel high thermal conductivity bonding material—ALD-Al₂O₃—on a 300 mm wafer.
Overview
This research aims to facilitate integration with next-generation 3D semiconductor device architectures, specifically the Backside Power Delivery Network (hereinafter referred to as “BSPDN”) and Reconstructed Die-to-Wafer (D2W) Hybrid Bonding. It was conducted to address key challenges such as insufficient thermal diffusion with conventional materials, the need to reduce bonding process costs, and the requirement to ensure sufficient bonding strength.
The focus of this research, ALD-Al₂O₃, exhibits higher thermal conductivity compared to conventional materials such as SiO₂ and SiCN, and enables direct bonding without CMP and plasma activation. This advancement enables process simplification and significant cost reduction, making it possible to realize highly reliable carrier wafer structures in 3D integration structures such as BSPDN. By serving as a stepping stone toward resolving thermal dissipation challenges, this technology is expected to enable higher integration density and improved energy efficiency in future 3D heterogeneous integration structures, thereby contributing to the continued advancement of semiconductor electronics.
This research was conducted under the “JST Adaptable and Seamless Technology Transfer Program through Target-driven R&D (A-STEP), Industry-Academia Collaboration, Project No. JPMJTR241A,” which was announced on March 12, 2025. The results were jointly presented by KOKUSAI ELECTRIC and YOKOHAMA National University at the IEEE 28th International Interconnect Technology Conference (IITC2025), the world’s leading conference on semiconductor interconnect technology, held in Busan, South Korea, from Monday, June 2 to Thursday, June 5.
Research Details
In this research, 5nm-thick Al2O3 films were deposited on a 300 mm silicon wafer using atomic layer deposition (ALD), and direct bonding was achieved without CMP and plasma treatment. The formation of a void-free bonding interface was confirmed through transmission electron microscopy (TEM) and ultrasonic inspection. The double cantilever beam (DCB) method in anhydrous condition was used to assess bonding strength, which is currently being standardized internationally under the leadership of YOKOHAMA National University, and the results demonstrated that sufficient strength was achieved. Furthermore, thermal desorption spectroscopy (TDS) analyzed that the Al₂O₃ film exhibits variations in water content and open-space volume depending on the deposition temperature, which significantly affect void formation at the bonding interface and the bonding strength. It was also confirmed that excessive water content in the film leads to void formation and saturation of bonding strength, whereas an appropriate amount of water promotes bond formation. In addition, the ALD-Al₂O₃ film demonstrated higher thermal conductivity than conventional SiO₂ (Figure 2), enabling a reduction in thermal resistance at the bonding interface and it is expected to contribute to improved thermal management in BSPDN structures. This technology presents a strong alternative to conventional bonding materials and serves as a promising process platform for overcoming thermal and mechanical challenges in 3D integration.
Figure 1: Schematic illustration of the newly proposed novel thin-film bonding technology
Figure 2: Demonstration of bonding on a 300 mm wafer and evaluation of thermal characteristics
Under the corporate slogan “Technology & Tai-wa for Tomorrow,” we will pursue economic, environmental, and social values from both business and ESG (resolving environmental and social issues and strengthening governance) aspects, with the aim of contributing to the achievement of SDGs and realizing a sustainable society and our group’s sustainable development.
Paper Information
Conference:
28th International Interconnect Technology Conference （IITC2025）
Title:
Novel Bonding Interfacial Material for Carrier Wafer of BSPDN & Reconstructed D2W Integration
Presenters:
Hayato Kitagawa1, Taisuke Yamamoto1, Jenyu Lee2, Shuntaro Machida2, Kazuhiro Yuasa2, Fumihiro Inoue1
1) YOKOHAMA National University, 2) KOKUSAI ELECTRIC CORPORATION