CityUHK pioneers breakthrough in 3DIC semiconductor packaging materials Strengthening Hong Kong’s role in next-generation semiconductor manufacturing technologies

With the rapid rise of emerging technologies such as AI, high-performance computing (HPC) and 5G,demand for improved chip performance and reliability continues to grow. A research team from CityUniversity of Hong Kong (CityUHK) has been awarded funding under the “RAISe+ Scheme” toaddress the complex metallisation challenges in the packaging of 3D integrated circuit (3DIC)semiconductor chips.

This groundbreaking research leverages patented chemical additives in the copper electroplating process, ensuring chip performance by achieving more stable connections in stacked chips. The teamplans to build an automated intelligent manufacturing line by 2026.

Caption: Led by Professor Tony Feng Shien-Ping from the Department of Systems Engineering at CityUHK, the research team developed a novel material to address the complex metallisation challenges in the packaging of 3D integrated circuit (3DIC) semiconductor chips. From right: Dr Mu Kaiyu, R&D Manager of Doctech, Ms Chang Yuhsueh, Research Assistant at CityUHK, Dr Yuen Muk-fung, R&D Manager, and Dr Huang Yu-Ting, CEO of Doctech. Photo credit: City University of Hong Kong

Led by Professor Tony Feng Shien-Ping, from the Department of Systems Engineering at CityUHK , the project is titled “Chemical Additive-Enabled Advancements in Electroplated Copper for Advanced Electronic Packaging and 3DIC Applications”. With the support of the “RAISe+ Scheme”, launched by the Government of the Hong Kong Special Administrative Region of the People’s Republic of China, the team seeks to accelerate the commercialisation of research outcomes,strengthen industrial applications, and solidify Hong Kong’s prominent position in the global advanced semiconductor supply chain.

Challenges in 3DIC semiconductor chip packaging

In the semiconductor industry, the number of transistors is a crucial indicator of enhanced computing power and performance. However, as the number of transistors increases, chip design encounters several challenges, including limitations in space, power consumption, heat dissipation and signal delays.

3DIC technology is regarded as a key approach to overcoming the limitations of traditional planar designs through vertical integration. This approach transforms the IC architecture from two dimensions to three, thereby enhancing performance, reducing power consumption and increasing the number of transistors per unit area. 

The key components of 3DIC technology include Through Silicon Via (TSV), redistribution layer (RDL), and direct copper-to-copper bonding (Cu-Cu bonding), which are essential for facilitating signal communication and power distribution between layers. To continue scaling down, challenges such as high bonding temperatures, copper surface oxidation and limited electromigration lifespan remain significant obstacles.

Caption: An illustration of 3DIC advanced packaging, showing key metal interconnect structures, including Cu-Cu bonding, RDL and TSV/TGV. The team aims to develop electroplating copper solutions to control material microstructures to address the metallisation challenges in 3DIC packaging. Photo credit: City University of Hong Kong

Four core innovations to enhance stability and efficiency

To address these challenges, the team aims to develop innovative packaging material solutions, including electroplating copper solutions that control material microstructures using patented chemical additives. This approach aims to enhance the performance and production efficiency of advanced 3DIC packaging.

The four technologies targeting the key issues of metal interconnection in 2.5D and 3DIC stacking are:

1. Metastable copper (MS-Cu): This enables Cu-Cu bonding at lower temperatures through nanograined Cu structures. This feature helps protect temperature-sensitive components, making it suitable for 3D stacking of such devices.

2. Dynamic covalent bond (DCB)-based coating material (DCB-coating): This coating provides temporary anti-oxidation protection for copper surfaces. It can be easily removed prior to Cu-Cu bonding to ensure clean, high-quality bonding interfaces.

3. Structural stable copper (SS-Cu): This technology improves resistance to surface corrosion and electromigration through composite Cu microstructures. Electromigration refers to the movement of atoms based on the flow of current through a material, which may cause a conductor to fail by forming voids. SS-Cu ensures the long-term reliability of high-density RDLs.

4. Nanoparticle with sulfur-bridge treatment (NP-S): This method enhances copper adhesion on glass substrates for Through-Glass Via (TGV) fabrication to achieve metallisation on glass substrates, paving the way for glass as a next-generation substrate for high-frequency device applications.

Over the next three years, the team aims to establish an automated intelligent production line and increase the capacity of existing additives and specialty chemicals to two tons per month. Professor Feng explained, “Our work introduces a new way to approach copper interconnection in 3DIC packaging. Instead of relying on high temperatures and conventional processes, we have developed materials and coatings that make bonding cleaner, faster and more reliable. This is not just an incremental improvement. It changes how sensitive devices can be stacked and protected, and it makes today’s breakthrough 3DIC technologies even more powerful for next-generation applications in advanced semiconductors.”

Caption: The project, led by Professor Tony Feng Shien-Ping (rear) from the Department of Systems Engineering at CityUHK has been awarded funding under the “RAISe+ Scheme”. Photo credit: City University of Hong Kong

Driving talent development, patents and industry impact

In addition to scientific innovation, the team plans to collaborate with local and international companies to expand applications in AI, telecommunications, automobiles and consumer electronics.

They aim to file from four to ten patents, ensuring that innovative solutions quickly translate into tangible contributions for society and the semiconductor industry.

“Our team has long been dedicated to research on advanced semiconductor packaging materials,”said Professor Feng. “Through this initiative, we aim to establish patents and production capacity and to nurture young research talent and deliver truly competitive solutions for both local and global markets.”

With the support of HK Tech 300, the innovation and entrepreneurship programme at CityUHK, the team established “Doctech HK Limited” and was awarded HK$1 million from HK Tech 300’s angel fund in 2023. It aims to become a supplier of next-generation electroplating chemicals and technologies for the semiconductor manufacturing and packaging industries, exemplifying how CityUHK’s research is being successfully translated into impactful commercial applications.

The 19th Hong Kong Youth Military Summer Camp and the 13th Hong Kong University Students Military Life Experience Camp held their joint opening ceremony on August 3rd at the People's Liberation Army (PLA) Hong Kong Garrison's San Wai Barracks, where approximately 500 young cadets took their oaths of enlistment.

This year, the two events have been merged and are being held simultaneously for a 14-day period. The Summer Camp has recruited about 350 students, while the Experience Camp has recruited approximately 150, bringing the total number of participants who have taken part in these programs over the years to more than 9,000.

The program includes military training, thematic lectures, site visits, and cultural and sports activities. The PLA Garrison aims to help the cadets deepen their understanding of the nation and its military, learn fundamental military skills, enhance discipline, and cultivate a strong sense of patriotism, while also strengthening exchanges and communication between the garrison and Hong Kong citizens.

Legislative Councilor Yiu Pak-leung, who is also a member of the Hong Kong Army Cadets Association Advisory Committee, noted that the activities provide cadets with knowledge of national defense and diplomacy. He expressed his hope that they will carry the steely resolve forged in the camp and contribute to the rejuvenation of the nation.

This year's student representative, Lau Wan-lung, expressed a mix of nervousness and excitement, as it was his first time participating. When asked why he joined, he said enthusiastically: "What I'm most looking forward to is handling a real gun. I'm really curious about holding one and doing the simulated shooting." He shared that he had been preparing beforehand, even practicing folding his blanket during lunch breaks. He joked, "Folding it into a tofu brick shape isn't going that well. I'm still practicing, but it's now within an acceptable range." He said he hopes the experience will help him get "fit" and fix his irregular sleep schedule.

Sze-to Cheuk-lam, a veteran of the 12th University Student Camp who is serving as a supervisor this year, said the greatest takeaway from training was learning about teamwork. Using marching as an example, she explained, "When many people march together, shouting the cadence, you can truly feel the spirit of unity through the shared experience with your comrades."

Fellow trainee and supervisor, Lu Yusi, is participating for the fourth time. She said she was inspired by her brother and her own love for challenges. "Fighting side-by-side for over ten days and developing a strong bond with our squad leader was an unforgettable experience."

She emphasized that being a supervisor is very different from being a trainee: "As a supervisor, you have to be mindful of the trainees' health and emotions. You can't just focus on yourself; you have to take care of others." She added that she has applied the lessons learned at the camp to her daily life: "I used to be a bit of a loner and found group activities troublesome. But actually, working together as a team can help you go much further."