Thin Film Applications via Atomic Layer Deposition (ALD) in Advanced Packaging Processes

  Mr. Zihao Li

  Process engineer，kokusai electric corporation    

Abstract: 

We propose the application of atomic layer deposition (ALD)-based thin films as a versatile solution for advanced packaging processes in next-generation 3D heterogeneous integration. As chiplet architectures evolve toward larger die sizes, finer pitches, and narrower gaps, increasingly complex interfacial conditions introduce critical challenges in underfill processing, including prolonged filling time, void formation, and reduced process reliability and productivity. Moreover, variations in surface materials often require multiple underfill formulations, increasing cost and reducing yield. To address these issues, ALD is introduced as a surface engineering technique capable of forming conformal, low-temperature thin films on diverse materials, thereby homogenizing interfacial conditions. By tuning surface wettability through post-treatment, the flow behavior of underfill materials can be systematically controlled, improving filling performance and suppressing defects. In addition, the ALD liner on microbump surfaces is expected to suppress metal migration, enhancing reliability in fine-pitch interconnects.

This study also highlights a novel direct bonding approach utilizing ALD-deposited Al2O3 as an adhesive layer. Although hybrid bonding enables fine-pitch scaling, higher bandwidth, and improved power efficiency, it still faces process complexity and cost challenges. Conventional materials such as SiO2 and SiCN require plasma activation and show degraded bonding strength with increasing queue time. The proposed approach eliminates plasma activation and mitigates queue-time dependence. Experiments using 300 mm wafers with queue times up to 60 days demonstrated stable bonding performance. A 5 nm Al2O3 film deposited at low temperature enabled direct bonding, with consistent bonding strength and no voids. These results demonstrate a robust, queue-time-free hybrid bonding approach, enabling flexible die-to-wafer integration and supporting scalable, cost-effective heterogeneous integration.

Speaker Biography:

Zihao Li earned a B.S. in Materials Science and Engineering from Dalian University of Technology in Dalian, China, and an M.S. in Materials Science from Tohoku University in Sendai, Japan. He currently works as a Process Engineer in the Advanced Technology Development Division at KOKUSAI ELECTRIC CORPORATION in Yokohama, Japan. His research focuses on applying atomic layer deposition (ALD) to advanced packaging, particularly for underfill flow control and thermal management.