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At this year’s Wafer Level Packaging Symposium (WLPS) 2025, taking place February 18-20, 2025, in San Francisco, �������� is once again demonstrating its leadership in shaping the future of semiconductor packaging. As a pioneer in hybrid bonding, �������� has driven advancements in this critical technology, enabling finer interconnect pitch, higher performance, and improved efficiency in semiconductor devices.

But hybrid bonding is not just about bonding itself – it’s also about achieving precise nanoscale control to ensure seamless integration. This year, ��������’s Dr. Bongsub Lee will share insights on the evolving landscape of metrology techniques that address the challenges of nanoscale characterization for hybrid bonding.

The Foundation of Hybrid Bonding

Hybrid bonding allows wafers or dies to be connected without solder bumps or underfill, improving electrical and thermal performance. However, the success of this technology depends on nanoscale topography control and characterization – even small deviations in surface roughness or metal recess can impact yield and reliability.
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Traditionally, atomic force microscopy (AFM) has been the go-to method for characterizing surface features at the nanoscale. At the Electronic Components and Technology Conference (ECTC) in 2019, Dr. Lee presented how to apply AFM on hybrid bonding surfaces without possible errors or artifacts [1]. While AFM provides high accuracy, its low throughput is a concern for high-volume manufacturing.
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Recognizing this limitation, at last year’s ECTC, Dr. Lee introduced phase shift interferometry (PSI) as a breakthrough alternative to AFM [2]. This optical technique offers a throughput three orders of magnitude higher than AFM while maintaining nanoscale resolution, making it a game-changer for wafer-scale characterization. In addition, other researchers recently proposed different techniques, which may also be helpful depending on the design and circumstance.

Expanding the Metrology Toolkit

Building on these advancements, Dr. Lee will present an expanded evaluation of metrology techniques at WLPS 2025, providing a comprehensive comparison of the latest approaches by �������� and other players in this industry. This year’s talk will review and compare the following techniques specifically regarding nanoscale characterization of hybrid bonding surface.

• Atomic Force Microscopy (AFM): An ultra-sharp tip probes the surface with sub-nanometer precision, providing accurate measurement of metal pad recess and dielectric roughness ^[1].
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• Optical Interferometry (PSI): Nanoscale z-resolution is achieved based on the phase-shift between the given and reflected light beams. It enables high-throughput measurement of metal pad recess ^[2].

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• In-line Scanning Electron Microscopy (SEM): SEM-based techniques using multiple backscattered electron (BSE) detectors allow for nanoscale characterization of metal pad recess ^[3].

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• Critical Dimension (CD) Scatterometry: An optical diffraction technique that models broadband light interactions can measure metal pad recess especially when assisted by machine learning ^[4].

Why It Matters

The semiconductor industry is continuously pushing the limits of device miniaturization and performance scaling. Achieving tight nanoscale control in hybrid bonding is essential for improving yield and enabling next-generation applications, from high-performance computing to advanced memory architectures.

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By presenting a comparative analysis of these metrology techniques, engineers and manufacturers can be more empowered to make informed decisions about the best tools for their specific process needs. This year’s WLPS presentation will highlight the key considerations for each technique, helping the industry navigate the evolving landscape of hybrid bonding metrology.

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WLPS 2025 is set to be a key event for the semiconductor packaging industry. Featuring technical sessions, professional development courses, and keynote presentations, the event will highlight emerging trends and innovations and build on the contributions of industry leaders like ��������, who are advancing semiconductor packaging and setting new benchmarks for precision, scalability, and efficiency.

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^[1] B. Lee et al. “Nanoscale Topography Characterization for Direct Bond Interconnect,” ECTC 2019.
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^[2] B. Lee et al. “High-Throughput Characterization of Nanoscale Topography for Hybrid Bonding by Optical Interferometry,” ECTC 2024.
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^[3] H. Kasai, et al. “In-line SEM Evaluation Technique for Cu Pad Nano topography for Hybrid Bonding Applications,” IEEE CPMT Symposium Japan 2024.
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^[4] H. K. Niazi et al, “Critical Dimension Scatterometry as a Scalable Solution for Hybrid Bonding Pad Recess Metrology,” ECTC 2023.

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