Introduction
Recently, the journal Nature Photonics, published by the Nature Publishing Group, featured a research article titled “High-power AlGaN deep-ultraviolet micro-light-emitting diode displays for maskless photolithography.” This study reports the development of the world’s first high-power, high-efficiency, high-resolution, high-pixel-density, and low-power deep-ultraviolet micro LED display array chip.
Advancements in Maskless Photolithography
Proposed Technique
Based on the display chip, the team proposed and realized a maskless photolithography technique using deep-ultraviolet micro LEDs, establishing a prototype platform for this process. They successfully fabricated the first deep-ultraviolet micro LED device using maskless exposure. This technology harnesses the advantages of high uniformity, high collimation, high power density, and high energy efficiency of deep-ultraviolet micro LED display chips.
Benefits for Semiconductor Manufacturing
The integration of the ultraviolet light source and the pattern on the mask traditionally required for photolithography provides sufficient irradiation dose for photoresist exposure in a short time, paving the way for revolutionary advancements in the semiconductor manufacturing industry.
The Importance of Photolithography in Semiconductor Manufacturing
Photolithography machines are critical equipment in the semiconductor manufacturing industry, widely used in producing integrated circuit chips. They utilize short-wavelength ultraviolet light to expose patterns on the photoresist film on semiconductor surfaces by penetrating the mask.
Global Demand and Challenges
In recent years, the global demand for high-performance chips has surged, intensifying competition among major powers. Traditional photolithography machines face challenges, including complex mechanical structures, large system sizes, and monopolization by developed countries, making them a “choke point” technology in the semiconductor industry.
Emergence of Maskless Photolithography
Low-cost, high-precision maskless photolithography technology has emerged as a hot research topic, offering flexible exposure pattern adjustments, diverse customization options, and cost savings in preparing photolithography masks. In this context, sensitive short-wavelength micro LED technology is particularly crucial for the independent development of semiconductor equipment.
Addressing the Challenges of Traditional Deep-Ultraviolet LED Light Sources
Limitations of Traditional Sources
Traditional deep-ultraviolet LED light sources face challenges such as large device size, low resolution, high energy consumption, low luminous efficiency, and insufficient optical power.
Collaborative Research Efforts
To address these issues, researchers from The Hong Kong University of Science and Technology, Southern University of Science and Technology, and other institutions collaborated to explore key areas such as reducing device size, improving light efficiency, and reducing power consumption.
Key Breakthroughs in Micro LED Technology
Development of Deep-Ultraviolet Micro LEDs
The team enhanced light extraction efficiency, thermal distribution performance, and epitaxial stress release through advanced manufacturing processes, achieving the following key breakthroughs:
High Power and High Efficiency
Using aluminum gallium nitride (AlGaN) material, the research team developed deep-ultraviolet (UVC) micro LEDs emitting light at a wavelength of 270 nm. With a minimum size of just 3×3 μm² and an external quantum efficiency of 5.7%, they achieved a maximum optical power density of 396 W/cm².
High-Resolution Pattern Display
The team developed a deep-ultraviolet micro LED display with a resolution of 320×140 and a pixel density of 2540 ppi (pixels per inch), utilizing CMOS active driving to display various exposure patterns.
Enhanced Display Performance
By integrating a back reflection layer and optimizing current distribution, the researchers significantly improved the screen’s luminous uniformity and beam shaping effect.
Rapid Exposure Capability
The first deep-ultraviolet micro LED maskless photolithography prototype was constructed. Testing showed that 1-micron-thick positive photoresist could be fully exposed within 3 seconds, comparable to traditional photolithography machines.
Application Demonstration
Based on this prototype platform, a semiconductor manufacturing solution was developed, resulting in the fabrication of the first blue micro LED array device using deep-ultraviolet maskless exposure.
Conclusion and Future Prospects
Compared to other representative works, this research reports smaller device sizes, lower drive voltages, higher external quantum efficiencies and optical power densities, larger array sizes, and higher display resolutions. These key performance enhancements place this research at a globally leading level. Currently, this maskless photolithography method based on deep-ultraviolet micro LED display technology has been successfully validated for use in manufacturing micro LED displays, laying a solid foundation for the conversion and application of the research’s technological achievements. This breakthrough will significantly reduce the high costs of photomask manufacturing while surpassing the efficiency of electron beam direct writing maskless exposure technology. This research signifies that deep-ultraviolet micro LED technology will bring about transformative changes in the semiconductor industry, initiating innovative solutions for maskless photolithography and is expected to drive revolutionary advancements in semiconductor manufacturing processes in the future.
Acknowledgments
This work was completed on March 12, 2023, submitted to Nature Photonics on April 18, 2023, and was officially accepted on September 12, 2024, after three rounds of practical validation. The team will continue to enhance the performance of AlGaN deep-ultraviolet micro LEDs and improve the prototype, developing 2K to 8K high-resolution deep-ultraviolet micro LED displays.
Funding and Support
Dr. Feng Feng from the State Key Laboratory of Advanced Displays and Optoelectronic Technologies at The Hong Kong University of Science and Technology is the first author, while Dr. Liu Zhaojun from the Department of Electronics at Southern University of Science and Technology is the corresponding author. Professor Guo Haicheng, founding director of the State Key Laboratory at Hong Kong University of Science and Technology, provided systematic guidance for this research. Researcher Xu Ke, Deputy Director of the Suzhou Institute of Nano-tech and Nano-Bionics, Chinese Academy of Sciences, and Deputy Director of the National Third Generation Semiconductor Technology Innovation Center (Suzhou), offered significant assistance. Professor Lars Samuelson, a foreign academician of the Chinese Academy of Sciences and an academician of the Royal Swedish Academy of Sciences and the Royal Swedish Academy of Engineering Sciences, provided valuable feedback on this research. Sitron Technology Co., Ltd. provided application demonstrations and industrialization support for this study.
This research was funded by the National Key R&D Program, the Guangdong Provincial Basic and Applied Basic Research Fund, and the Shenzhen Science and Technology Fund Project. It also received platform support from the Nano-System Manufacturing Laboratory (NFF), Material Characterization and Preparation Center (MCPF), and Electronic Packaging Laboratory (EPACK Lab) at The Hong Kong University of Science and Technology, as well as the Public Testing and Analysis Center at Southern University of Science and Technology.
Original: https://doi.org/10.1038/s41566-024-01551-7
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