Recently, SiTan Tech, a leading player in the semiconductor sector, participated in a groundbreaking innovation—High-Power AlGaN Deep-Ultraviolet Micro LED Displays for Maskless Photolithography, which was published in the prestigious scientific journal Nature Photonics.
(Nature Photonics Original Article: https://www.nature.com/articles/s41566-024-01551-7).
This milestone achievement has sparked widespread interest in the semiconductor industry, with hundreds of media outlets reporting on it. But what exactly is this technology, and what makes it such a revolutionary advancement in the semiconductor field? In this article, we’ll break it down for you.
CONTENTS
- Why is the Lithography Machine Called the “Heart” of Integrated Circuit Manufacturing?
- What is a Mask?
- What is Maskless Lithography?
- Long-term Collaborative Efforts on Deep UV Micro-LED Light Sources
- What Key Breakthroughs Have We Achieved?
- What Is the Significance of These Breakthroughs?
1. Why is Lithography So Important?
Lithography machines are core equipment in modern integrated circuit manufacturing. Think of it as a highly precise “camera” that projects circuit patterns onto silicon wafers, creating the intricate microstructures that form the foundation of chip functionality.
Since photolithography determines the key dimensions of a chip, it directly impacts its precision and performance. As the feature size of modern integrated circuits has reached the nanometer scale, the precision required from lithography machines is extremely high. Even the smallest error could cause chip failure. For this reason, photolithography is often referred to as the “heart” of integrated circuit manufacturing. The cost of photolithography accounts for about 30% of total processing costs, and it consumes around 45% of the production time, with costs continuing to rise.
Among all aspects, the cost of photomasks has been rising at the fastest rate.
2. What Is a Photomask?
A photomask, much like a camera film, is a graphic transfer tool or master used in the microelectronics manufacturing process. It is etched with intricate circuit patterns, which are then projected onto a silicon wafer through exposure, similar to how a photographic film projects an image onto paper.
However, in the chip manufacturing process, exposure is not completed in a single step—it requires multiple exposures. Each exposure step requires a different photomask, and precise alignment of the mask with the silicon wafer is necessary, making accurate positioning a major technological challenge.
In summary, the production of photomasks is complex, time-consuming, and expensive. Once made, they cannot be modified. As technology complexity increases, costs naturally rise.
Therefore, to make the photolithography process more flexible, researchers began investigating whether it’s possible to replace physical masks with alternative technologies. The goal? To eliminate the need for photomasks altogether.
3. What Is Maskless Lithography?
Since the 1990s, low-cost, high-resolution maskless lithography has become one of the cutting-edge areas of lithography research.
Currently, there are two main types of maskless lithography, categorized based on the light source: One is based on charged particle beams, including electron beam lithography (EBL) and ion beam lithography (IIBL). The other is based on light waves for projection exposure, which includes technologies such as interference lithography (IL), laser direct writing (LDW), and spatial light modulator (SLM) lithography.
Each of these technologies has its own advantages, but they all face the challenge of “not being suitable for mass production.” On the one hand, charged particle beam lithography has low production efficiency and causes significant proximity effects in large-scale production, which severely impacts the resolution and precision of patterns. On the other hand, laser direct writing lithography is limited by laser wavelength and is not as precise as charged particle lithography, making it unsuitable for the manufacturing of advanced semiconductor devices.
So, what about other possibilities? Are there new technologies on the horizon?
In recent years, the rapid development of Micro-LED technology has introduced a new path and method. Each Micro-LED boasts features like high energy density, high resolution, high integration, and low energy consumption. The question then arises: Can Micro-LEDs be used for high-precision deep ultraviolet lithography?
4. Long-term Collaborative Efforts on Deep UV Micro-LED Light Sources
In fact, deep ultraviolet (UV) LED light sources have already been applied in some areas. However, traditional deep UV LEDs have challenges such as large device sizes, low resolution, high energy consumption, low light efficiency, and insufficient light power.
To address these challenges, a collaborative effort involving Hong Kong University of Science and Technology, Southern University of Science and Technology, National 3rd Generation Semiconductor Technology Innovation Center (Suzhou), and SiTan Tech was launched.
The team discovered that the size of the deep UV Micro-LED directly affects both resolution and light power. Smaller sizes can achieve higher resolution, but typically result in lower light power. Solving this issue would not only advance Micro-LED applications in next-generation displays, but also pave the way for maskless lithography.
Over the years, the team has conducted extensive research into deep UV Micro-LEDs, exploring key areas such as reducing device size, enhancing light efficiency, and lowering power consumption.
Relevant studies are as follows:
https://doi.org/10.1109/LED.2021.3130750
https://doi.org/10.1063/5.0123409
https://doi.org/10.1002/jsid.1107
5. What Key Breakthroughs Have We Achieved?
In this study published in Nature Photonics, the team utilized advanced manufacturing techniques to improve light extraction efficiency, thermal distribution performance, and epitaxial stress release, achieving the following key breakthroughs:
- High Power and High Efficiency: To meet the needs of high-power and high-efficiency lithography applications, the team developed deep UV (UVC) Micro-LEDs made from AlGaN materials. These Micro-LEDs have a light emission wavelength of 270 nm, a minimum size of just 3×3 μm², an external quantum efficiency of 5.7%, and a peak light power density of 396 W/cm², overcoming previous limitations in light source intensity and ensuring the necessary irradiation energy for lithography.
- High-Resolution Pattern Display: The team developed a deep UV Micro-LED display with a resolution of 320×140 and a pixel density of 2540 ppi, using CMOS active driving to display various exposure patterns. This demonstrates its potential in maskless lithography and other high-precision applications.
- Improved Display Performance: By integrating a back-reflection layer and optimizing current distribution, the team significantly improved the uniformity and beam-shaping effect of the display, ensuring stable performance across all areas of the screen.
- Fast Exposure Capability: The team built the first deep UV Micro-LED maskless lithography prototype, which can fully expose 1-micron-thick positive photoresist (AZ MiR 703) in just 3 seconds. This is on par with traditional step-and-repeat lithography machines that use photomasks. By increasing the power, the prototype’s exposure energy density can be significantly enhanced, reducing exposure time to milliseconds. This rapid exposure is thanks to the superior photoelectric performance and light extraction efficiency of Micro-LEDs, which ensures the practical application of deep UV Micro-LED maskless exposure in semiconductor manufacturing.
Compared to other representative works, this study reports smaller device sizes, lower drive voltages, higher external quantum efficiency, light power density, larger array sizes, and higher display resolutions. These performance improvements place the study’s achievements at the forefront globally.
6. What Is the Significance of These Breakthroughs?
Currently, based on this maskless lithography prototype, a semiconductor manufacturing solution has been developed to produce the first deep UV Micro-LED maskless exposed blue Micro-LED array device (Micro-LED made by Micro-LED), which has been successfully verified for use in Micro-LED display manufacturing.
This successful application will significantly reduce the high cost of photomask production, while vastly improving efficiency compared to electron beam direct-write maskless exposure technology.
More significantly, this research marks the beginning of a new era for deep UV Micro-LED technology, providing innovative solutions for maskless lithography, which is a revolutionary advancement for industries including semiconductor manufacturing.
Moving forward, the SiTan Tech team will continue to enhance the performance of AlGaN deep UV Micro-LEDs, improve the prototype machine, and develop 2K-8K high-resolution deep UV Micro-LED display products, providing more efficient and cost-effective chip manufacturing solutions for the semiconductor industry and helping to accelerate the global upgrade of technology industries.
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