Sessions Index

Bio:

Prof. Chih Chen is currently the chair professor in Dept. of Materials Science and Engineering, National Yang Ming Chiao Tung University (NYCU).
Chih Chen received his Ph.D. degrees in Materials Science of University of California at Los Angeles (UCLA) in 1999 in Prof. King-Ning Tu’s group. He joined NYCU Taiwan in 2000 and served as the Chairman of Department of Materials Science and Engineering in NYCU from Feb. 2017 to Jan. 2023. Professor Chen discovered electrodeposition of (111)-oriented nanotwinned Cu, and reported it in Science 336, 1007-1010 (2012), and transferred the technology to Chemleaders, Inc, Taiwan for mass production in 2016. Therefore, he received the 2016 National Innovation Award, 2016 Materials Innovation Award, Materials Research Society, Taiwan, 2017 Outstanding Technology Transfer Award on Electroplating and Application of High (111)-oriented Nanotwinned Cu, 2018 & 2023 Outstanding Researcher Award from National Science & Technology Council Taiwan, TMS 2018 Research to Practice Award from The Minerals, Metals & Materials Society (TMS, USA). He was recognized as fellow of International Association of Advanced Materials (IAAM) in 2020 and Fellow of The Materials Research Society-Taiwan (MRS-T) in 2022.
His current research interests are low-temperature Cu-to-Cu direct bonding, high strength nanotwinned Cu lines and films for 3D IC integration, reliabilities of flip-chip solder joints and microbumps for microelectronics packaging, including electromigration, thermomigration, and metallurgical reactions. He published 200+ journal papers and he holds 35+ Taiwan and US patents. He wrote a book with Prof. King-Ning Tu and Prof. H.M. Chen on Electronic Packaging Science and Technology, which has been published by Wiley in 2021.

Abstract:

As the dimensions of Cu hybrid joints continue to shrink, the bonding process faces significant challenges. One major issue is the limited thermal expansion of Cu pads within dielectric vias, as most of the Cu volume adheres to the via sidewalls. This restriction narrows the bonding process window. Fine-grained Cu (FG-Cu) offers a promising solution to this limitation.

In this presentation, we will discuss the electrodeposition of FG-Cu into SiO₂ vias and analyze the resulting grain size distribution. In-situ heating atomic force microscopy (AFM) was employed to measure the thermal expansion behavior of FG-Cu pads embedded in SiO₂ vias. The results reveal that FG-Cu exhibits excellent thermal expansion capability, attributed to its high creep rate at relatively low temperatures.

Furthermore, bonding between FG-Cu pads and FG-Cu films will be demonstrated, showing that NC-Cu effectively reduces interfacial void formation. Finally, the thermal stability and oxidation behavior of FG-Cu will also be addressed.

 

 

Bio:
Masao Tomikawa joined Toray Industries, Inc. after earning a master's degree from the University of Tokyo. Studied at the University of Akron in the United States from 1992 to 1994. In 2007, he was certified as a research fellow at Toray Industries, Inc., and then became a director of Toray Industries, Inc. in 2020 and a senior fellow at Toray Industries, Inc. in 2024. During this time, he obtained a doctor degree from the Tokyo Institute of Technology in 2011 and became a fellow of the Society of Polymer Science in 2019. His specialties are polymer synthesis, physical properties, and photosensitive design. Awards 1991: Society of Polymer Science Technology Award 2009: Chemical Technology Award, Chemical Society of Japan 2015: National Invention Award, Japan Institute of Invention and Innovation 2018: Best Paper Award Pan Pacific Microelectronics Symposium 2020: Achievement Award, Photopolymer Society of Japan 2020: Minister of Education, Culture, Sports, Science and Technology Award.

Abstract:
Hybrid bonding technology is attracting attention as a next-generation high-density mounting technology. This technology has already been used to improve the performance of CMOS image sensors by bonding wafers together using inorganic insulating films such as copper and copper, and SiO2 and SiO2. (1) Further development is being considered for use in three-dimensional stacking of semiconductor chips of different functions and sizes. In such applications, it is considered to bond chips onto wafers, and in addition to being able to do so at low temperatures and with low warpage, tolerance to fine foreign matter is important.
We have created a process using flexible resin with hybrid bonding technology that is resistant to nano scale particles, and have demonstrated that a yield of nearly 100% can be obtained even when bonding blade-diced chips and have not been adequately controlled for fine particles. Furthermore, bonding is possible at low temperatures of less than 250°C, and warpage is about one-third smaller than in the SiO2-SiO2 process, so we believe that this technology is suitable for hybrid bonding of chips and wafers or chips and interposers (2).
It has been reported that in hybrid bonds, polar groups generated by plasma activation during the annealing process after SiO2-SiO2 bonding undergo chemical reactions, generating water and creating voids (3). In polyimide materials, polar components are also generated by plasma activation, which creates chemical bonds, and water may be generated in the same way as in SiO2. Organic materials have higher gas permeability than inorganic materials, and it is thought that organic materials can eliminate the generated water vapor. Quantifying this characteristic is important in discussing device reliability. In this study, we investigated the generation and movement of water during the hybrid bonding process.
A polyimide material (PI-1), which can be cured at a low temperature process below 250 °C, was used as the dielectric layer for the hybrid bonding lamination process. The insulation reliability of this material was confirmed by bias-highly accelerated stress testing (B-HAST) with 1 μm L&S (4).
Based on previous studies, it is estimated that hydrophilization occurs in polyimide materials as well as conventional inorganic materials during the surface activation process by plasma treatment, and chemical bonds are formed between polymers and polymers and between polymers and SiO2 during the TCB and post-annealing processes, generating water. PI-1 was surface-activated by plasma treatment, and the hydrophilicity of the surface was confirmed by X-ray photoelectron spectroscopy (XPS) and surface free energy (SFE) analysis. This suggests that water is generated by chemical bond formation during the bonding and annealing processes. Assuming that the thickness of the active layer is 5 nm from the surface, it can be estimated that a maximum of about 1.2 ng/cm² of H₂O is generated. To determine whether this water can be removed to the outside, the amount of water vapor permeated through the PI-1 film was measured using the following method.
The amount of water vapor permeating the PI-1 film was measured using a differential pressure steady-state method at temperatures of 25, 70, 110, and 150°C respectively. The water permeability coefficient of PI-1 under each obtained condition was in good agreement with the Arrhenius equation, as theoretically predicted [5]. Using this approximation, the water vapor permeability coefficient at process temperatures of 200°C to 250°C was estimated. According to these results, the vapor pressure of the evaporated H₂O generated at the PI-1 interface during annealing at 250 °C for 1 hour is calculated to be 3.98 MPa. Assuming that the PI-1 film thickness is 5 µm and the chip size is 6 mm × 6 mm, the amount of water permeation is roughly estimated to be more than 1 µg, which is nearly 1000 times the amount of water generated above. This means that all of the H₂O generated at the bonding interface may permeate out of the film. In addition, when considering the amount of water generated, it is necessary to consider the water absorption and imidization rate of the polyimide film. The amount of H₂O absorbed by the film and the amount of H₂O generated by the imidization reaction of the polyimide precursor during curing were also estimated. Then, the temperature and time conditions required for the permeation and release of H₂O from the film were examined. The results are reported in this full paper

 

Bio:
Yi-Chen Chung is a Ph.D. student at National Yang Ming Chiao Tung University under the supervision of Prof. Chih Chen. His research focuses on advanced packaging technologies, with an emphasis on Cu/SiO₂ hybrid bonding and Cu-Cu bonding for 3D integration. He has collaborated with the Industrial Technology Research Institute (ITRI) on interconnect reliability and metrology development. In this presentation, he will discuss the thermal deformation behavior of fine-pitch Cu/SiO₂ hybrid bonding structures, characterized using variable temperature atomic force microscopy (VT-AFM). His work highlights the critical role of CMP-induced topography in ensuring thermal-mechanical reliability for next-generation 3D IC packaging.

Abstract:
As the demand for ultra-high-density 3D integration and chiplet-based system architectures continues to escalate, hybrid bonding has emerged as a key enabler for fine-pitch vertical interconnects. Copper (Cu) and silicon dioxide (SiO₂) are commonly used materials in these bonding structures due to their excellent electrical and mechanical properties. However, the inherent mismatch in their coefficients of thermal expansion (CTE) poses significant challenges in maintaining interfacial planarity and structural reliability under thermal stress. Moreover, when Cu interconnects are fabricated using damascene processes and embedded within dielectric matrices, precise control over surface topography—particularly dishing—is critical for ensuring robust bonding performance.
In this study, we present a comprehensive evaluation of thermal expansion behavior in fine-pitch Cu/SiO₂ hybrid bonding structures fabricated through a damascene process. The test samples consisted of 2 µm Cu pads with a 4 µm pitch, planarized using an optimized chemical mechanical planarization (CMP) process to control Cu dishing depth to less than 5 nm. Such strict dishing control is necessary to satisfy bonding surface requirements.
To investigate the thermal deformation characteristics of these structures, we employed variable temperature atomic force microscopy (VT-AFM), a nanoscale metrology tool capable of measuring surface expansion with sub-nanometer resolution under elevated temperatures. Each sample was subjected to two thermal cycles from room temperature to 200 °C and then cooled down to room temperature, simulating thermal loading conditions typically encountered during hybrid bonding and subsequent packaging processing steps.
VT-AFM measurements revealed that the damascene-embedded Cu pads exhibited a repeatable out-of-plane expansion of approximately 2–3 nm during each thermal cycle. Importantly, the degree and uniformity of expansion were closely correlated with local CMP outcomes: Cu pads with smoother and more uniform surfaces showed stable and symmetric expansion behavior, while those with slight dishing non-uniformities developed localized bulging or asymmetric deformation. These effects are primarily attributed to the CTE mismatch between Cu and SiO₂, which introduces differential stress at the interface—especially in regions where surface planarity is compromised.
The results highlight the importance of not only achieving sub-5 nm dishing control during CMP but also validating the thermal-mechanical behavior of the Cu/SiO₂ system using temperature-resolved surface metrology. Our findings show that even minor variations in surface topography can translate into measurable thermally induced distortion, which may influence bonding alignment accuracy and long-term reliability in 3D packaging applications.
This work demonstrates a systematic approach for assessing fine-pitch hybrid bonding readiness by combining advanced planarization control and VT-AFM-based thermal analysis. The integration of these techniques provides a powerful methodology to both ensure and validate the structural integrity of Cu/SiO₂ hybrid bonding interfaces. These insights will be critical for the development of next-generation 3D IC packaging platforms where ultra-fine pitch and sub-nanometer flatness are essential.

 

Bio:
Joonho You is currently the CEO of Nexensor Inc. He studied optical metrolgoy at KAIST (Korea Advanced Institute of Science and Technology) and has over 20 years of experience in research, development, and commercialization in this field. His research interests include interferometry technology, thin-film measurement technology, shape measurement techniques using pattern projection methods such as deflectometry and Moiré, and fiber optic-based thickness sensors. He is the member of The Korean Microelectronics And Package Society and Korean and Optical Society of Korea

Abstract:
This study introduces a hybrid metrology technique that integrates Phase Shifting Interferometry (PSI), a well-established optical measurement method, with Active Probe-based Atomic Force Microscopy (AP-AFM). PSI is widely used for precise characterization of surface features such as roughness, step heights, and refractive index distributions in both research and industrial semiconductor applications. The technique offers several key benefits, including nanometer-level vertical resolution, high throughput, non-contact operation, and full-field imaging, making it an essential tool in wafer-scale process control. Notably, it plays a central role in Chemical Mechanical Polishing (CMP) quality assessment, where surface defects such as dishing and erosion must be rigorously monitored.

However, while PSI excels in many respects, its measurement performance can be significantly degraded by a range of error sources. These include phase-shift inaccuracies due to mechanical or environmental instabilities, susceptibility to external vibrations, non-linearity in detector response, parasitic reflections within the optical path, digital quantization noise, laser frequency instability, and fluctuations in illumination intensity. These error mechanisms become particularly problematic when inspecting topographies involving spatially varying refractive indices or complex multilayer structures, which are increasingly common in advanced semiconductor packaging and interconnect schemes.

To address these fundamental limitations, we propose a synergistic approach that combines PSI with Atomic Force Microscopy. Specifically, we adopt an AFM architecture based on integrated active probes (APs), which circumvent the need for conventional Optical Beam Deflection (OBD) systems. The OBD approach, while effective in many standalone AFM systems, introduces bulky optics that make co-integration with PSI impractical, particularly in constrained wafer metrology environments. In contrast, the AP-AFM technology developed by nano analytik GmbH utilizes MEMS-based cantilevers equipped with integrated piezoresistive sensors for displacement readout and built-in actuation capabilities. This design dramatically reduces system complexity and size, enabling seamless integration with optical metrology setups.

The active probes feature highly durable tip materials such as gallium nitride (GaN) and diamond, ensuring long operational lifetimes and the ability to sustain atomic-resolution imaging over extensive usage. These properties are critical for semiconductor process control, where both high resolution and probe robustness are necessary to minimize downtime and ensure consistency in measurement performance. Importantly, AFM's imaging fidelity is unaffected by optical refractive index variations in the sample, making it a powerful complement to PSI for heterogeneous material systems.

This integrated metrology platform effectively combines the fast, wide-area scanning capabilities of PSI with the ultra-high-resolution, localized measurement power of AFM. It provides a unique pathway to real-time, traceable inspection workflows capable of resolving nanometer-scale surface features across large fields of view. This dual-modality system opens new possibilities in semiconductor fabrication, including advanced CMP process tuning, defect localization and classification, and 3D interconnect metrology. Furthermore, the approach has potential applicability in other precision manufacturing sectors where both speed and atomic-scale accuracy are simultaneously required. By leveraging the complementary strengths of optical and mechanical measurement techniques, the proposed hybrid system represents a significant advancement in next-generation metrology for nanotechnology and beyond.

 

Bio:
Heng-Ching Mie is a PhD student from Mizuno Lab at the Semiconductor Academy, National Cheng Kung University. His research focuses on advanced packaging, interfacial adhesion, Through-Glass Via (TGV) reliability, and hybrid bonding. The lab collaborates with industry partners to develop innovative solutions for next-generation heterogeneous integration.

Abstract:
SiO2 is widely used as a dielectric layer in the heterojunction process due to its excellent compatibility with silicon-based semiconductor and insulating properties. However, the significant mismatch in the coefficient of thermal expansion (CTE) and mechanical strength with copper give rise to several reliability issues such as wafer flatness issue and interface reliability during Cu/SiO2 hybrid bonding process [1, 2]. With the ongoing trend toward device miniaturization and higher operating temperature the mentioned issue became more critical [3]. When the processing temperature is concerned, SiO2 further demonstrates its disadvantage.
In this study, we investigated Cu/dielectric hybrid bonding using polyimide (PI) as the dielectric layer, employing various surface treatments, including citric acid and O₂ plasma treatments, to enhance bonding performance. The effects of surface treatments were investigated through comprehensive surface characterization, including surface morphology analysis via atomic force microscopy (AFM) and contact angle measurements. Chemical composition analysis are done by X-ray photoelectron spectroscopy (XPS) investigating. Final mechanical property is accessed through shear strength testing with the DAGE SERIES 4000PXY system.
The study demonstrates that the shear strength of PI/PI interfaces is primarily governed by surface roughness. When high-energy O₂ plasma interacts with the PI surface, ion bombardment induces significant changes in surface topography, thereby increasing the effective contact area. However, excessive roughness leads to the formation of interfacial voids, which severely deteriorate the bonding strength. Notably, at comparable levels of surface roughness, samples treated with 50 W plasma exhibit higher shear strength, attributed to enhanced surface hydrophilicity. This is supported by both XPS spectra and contact angle measurements: the 50 W treated samples display a greater degree of hydrophilicity compared to those treated at 30 W. Specifically, the 50 W treatment results in an increased concentration of carbonyl oxygen species, and a corresponding reduction in contact angle when measured with deionized water.
Regarding citric acid treatment, although citric acid has no significant effect on chemical composition of PI as others suggested, the removal of copper oxide, which will severely effect the bonding strength, have found to be very effective. After citric acid treatment, XPS spectrum show that Cu-O bond has nearly disappeared and a near 98% of Cu is presented on the surface, giving a suitable condition for Cu-Cu direct bonding.
Under optimized bonding conditions (225 °C, 44.4 MPa), a shear strength of approximately 19 MPa was achieved for pure PI/PI bonding with appropriate O₂ plasma treatment. Under the same bonding conditions, Cu pillar embeded samples treated with O₂ plasma and citric acid achieved a shear strength of approximately 20 MPa. Demonstrating the effectiveness of surface treatment strategies in enhancing the reliability of Cu/PI hybrid bonding.

 

Bio:
Chih-Chi Tsai is a Ph.D. student in the Department of Materials Science and Engineering at National Yang Ming Chiao Tung University, Taiwan. She is a member of the Advanced Packaging Laboratory, supervised by Prof. Chih Chen. Her research focuses on co-electrodeposition processes, including electromigration and grain growth mechanisms in electroplated materials.

Abstract:
As the development of advanced semiconductor packaging continues to push the boundaries of device miniaturization and integration density, the selection of interconnect materials with high electrical conductivity, mechanical strength, and thermal reliability becomes increasingly critical. Nanotwinned copper (NT-Cu) has emerged as a promising interconnect candidate due to its high twin boundary density, superior electromigration resistance, and enhanced thermal stability. In particular, the presence of coherent twin boundaries in highly <111>-oriented NT-Cu structures is known to significantly retard grain boundary diffusion while maintaining low resistivity. However, thermal annealing during backend processing may lead to undesired grain growth and twin coarsening, which deteriorate the beneficial nanostructure and reduce long-term device reliability.
To address these challenges, this study explores the influence of various transition metal dopants on the annealing behavior of electroplated NT-Cu films. Specifically, iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn) were selected as dopants due to their differing atomic radii and diffusivity in Cu matrices. All dopants were introduced into the plating bath at a concentration of 0.05 M. The electrolyte was prepared using copper sulfate pentahydrate (CuSO₄·5H₂O, 0.5 M), sulfuric acid (H₂SO₄, 100 g/L), hydrochloric acid (HCl, 30 ppm), and a commercial organic additive (108C, 45 mL/L). The co-electroplating processes were carried out at room temperature using direct current (DC) with a current density of 6 ASD for 300 seconds. A Ti diffusion barrier and 200 nm Cu seed layer were first deposited on 4-inch silicon wafers to ensure good adhesion and uniform nucleation.
Following deposition, thermal annealing was performed in a quartz tube furnace under high vacuum (10⁻³ Torr). Three annealing conditions were investigated: (1) 230°C for 3 hours, (2) 300°C for 1 hour, and (3) 350°C for 1 hour. The evolution of grain morphology and twin density was examined using focused ion beam (FIB), scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD). Our goal was to assess how each dopant influences grain growth kinetics, twin formation, and microstructural stability at elevated temperatures relevant to Cu-Cu bonding and fine-pitch hybrid interconnects.
The results indicate distinct behaviors among the different dopants. Fe, Co, and Ni additions all promoted noticeable grain growth even at the lower annealing temperature of 230°C. At 300°C and 350°C, these doped films exhibited large, coarse grains with diminished twin boundaries, implying a loss of the desired nanostructure. These changes were attributed to enhanced atomic mobility facilitated by the dopants, which accelerated recrystallization and grain boundary migration. In contrast, Mn-doped Cu films maintained a relatively stable fine-grained structure under the same conditions. Even after annealing at 350°C, Mn addition suppressed abnormal grain growth and preserved a portion of the twin boundary network, suggesting an inhibitory effect on grain boundary movement and dislocation activity.
This study has demonstrated that different transition metal dopants significantly influence the annealing behavior and grain growth kinetics of electroplated NT-Cu films. Building on these findings, future work will aim to harness dopant-induced microstructural effects to enhance Cu–Cu bonding quality. In particular, we plan to investigate whether grain growth across the bonding interface can be achieved through low-temperature annealing, thereby improving interfacial strength and reliability. To this end, three key directions will be pursued: (1) optimizing annealing parameters at reduced temperatures to promote grain boundary migration across Cu–Cu interfaces; (2) correlating interfacial microstructure with bonding strength through mechanical testing and cross-sectional analysis; and (3) exploring novel additives or process modifications to enable robust bonding under tighter thermal budgets. Through these efforts, we aim to develop a more reliable low-temperature Cu–Cu bonding strategy that supports the demands of next-generation fine-pitch interconnects and advanced packaging technologies.

 

Bio:
From: Department of Materials Science and Engineering, NYCU Advisor: Prof. Chih Chen Research direction: Cu/SiCN hybrid bonding

Abstract:
The growth of artificial intelligence (AI) and 5G networks drives the need for finer interconnect pitch at both wafer and die levels. Hybrid bonding stands out as a key technology to meet this demand, enabling high performance, greater efficiency, and reliable signal transmission for advanced semiconductor integration. Hybrid bonding involves the direct bonding of dielectric pads followed by annealing of Cu vias. The recess of copper and dielectric pads needs to be well-controlled. The roughness of both copper pads and dielectric pads are crucial for the bonding process. To meet the bonding requirements in morphology and surface roughness, we adopted chemical mechanical planarization (CMP) as the surface planarization method.

One of the focuses of this study is to optimize the CMP process by tuning the relative removal rates of the Cu, barrier, and bonding dielectric layer. By adjusting the slurry pH, we were able to control the selectivity between these materials. In addition, dilution of the slurry concentration is employed to more specifically control the polishing rate. Achieving a well-balanced removal rate among these materials is essential to minimize recess depth and ensure uniform planarization across the bonding interface.

Currently, Cu/SiO2 hybrid bonding is the most widely adopted and well-researched technology. However, we selected silicon carbon nitride (SiCN) as the bonding dielectric due to its superior properties, including higher bonding strength, void suppression capability, and effectiveness as a copper diffusion barrier. Additionally, nanotwinned copper (NT-Cu) was used as the metal pad material owing to the high surface diffusivity, low oxidation rate, and high strength compared to conventional Cu. Most of all, the higher coefficient of thermal expansion (CTE) can tolerate slightly larger recess depths without compromising bonding quality.
The thermal expansion behavior of copper pads embedded within dielectric vias plays a crucial role in achieving bonding integrity during the thermal annealing process. Both in-situ and ex-situ heating atomic force microscopy (AFM) measurements were performed to characterize the surface profiles to examinate the coefficient of thermal expansion.
This study provides a more comprehensive understanding with direct evidence of the Cu/SiCN hybrid bonding mechanism.