On the left is the industry-standard model currently in use; on the right is the OIST model. This innovation, with a simple design of just two mirrors, significantly improves stability and maintainability, and requires only a 20W light source, keeping the total system power consumption to less than 100kW – one-tenth of conventional technologies that often require more than 1mW to operate. The new system also reduces 3D effects in the mask while maintaining very high contrast, enabling the nanometer precision needed to precisely transfer logic patterns from photomasks to silicon wafers. Credit: Shintake Tsumoru, 2024
Professor Tsumoru Shintake of the Okinawa Institute of Science and Technology Graduate University (OIST) has proposed an extreme ultraviolet (EUV) lithography technology that exceeds the standard for semiconductor manufacturing.
EUV lithography based on this design will operate with a smaller EUV source, reducing costs and significantly improving machine reliability and lifetime, while consuming less than one-tenth the power of conventional EUV lithography machines, helping to improve the environmental sustainability of the semiconductor industry.
This technology was made possible by solving two problems previously thought insurmountable in this field: first, a new optical projection system consisting of only two mirrors, and second, a new way to efficiently deliver EUV light to the logic pattern on a flat mirror (photomask) without interrupting the light path.
Challenges Surrounding EUV Lithography
Advanced semiconductor chips such as processors that enable artificial intelligence (AI), low-power chips used in mobile devices such as mobile phones, and high-density DRAM memory used in machines that are indispensable to our lives are all manufactured using EUV lithography. However, semiconductor manufacturing is problematic due to its high power consumption and the complexity of the equipment, which significantly increases the cost of installation and maintenance as well as power consumption.
“This invention is a groundbreaking technology that can almost completely resolve these little-known problems,” Professor Shintake said.
In conventional optical systems, such as cameras, telescopes, and conventional ultraviolet lithography, optical components such as apertures and lenses are arranged in a line with axial symmetry (symmetrical about a central axis). This configuration ensures the best optical performance with minimal optical aberrations, resulting in high-quality images. However, this method is not suitable for EUV light, which has a very short wavelength and is absorbed by most materials, so it cannot pass through a transparent lens.
To achieve this, EUV light is transmitted through space using crescent-shaped mirrors that reflect it in a zigzag pattern along its path (see diagram below). However, this method moves the light off-axis, sacrificing important optical properties and reducing the overall system performance.
To address this issue, the new lithography technique uses two axially symmetric mirrors with small central holes aligned in a straight line, providing superior optical properties.
Significant reduction in power consumption
EUV energy is highly absorbed, so it is attenuated by 40% with each mirror reflection. Industry standards allow only about 1% of the energy from an EUV source to pass through the 10 mirrors and reach the wafer. This means that very high EUV light output is required. To meet this demand, a large amount of power is required to drive the CO2 laser in the EUV source, and a large amount of water is required for cooling.
On the other hand, by limiting the number of mirrors from the EUV source to a total of four, more than 10% of the energy passes through, allowing a compact EUV source with an output of tens of watts to operate with similar efficiency, thus significantly reducing power consumption.
Overcoming two challenges
The heart of EUV lithography is the projector, which transfers the image from the photomask onto the silicon wafer, and consists of just two reflecting mirrors, like an astronomical telescope.
“Considering that a conventional projector requires at least six reflecting mirrors, this configuration is unimaginably simple. It was made possible by a careful rethinking of the theory of aberration correction in optics. This is a triumph of classical physics before quantum physics,” explains Professor Shintake.
“Performance has been verified using optical simulation software (OpTaliX) and is guaranteed to be sufficient for advanced semiconductor manufacturing.”
Professor Shintake solved this problem by devising a new illumination optical system called “dual line field,” which irradiates EUV light from the front side of the flat mirror photomask without obstructing the light path.
Professor Shintake explains: “If you hold a flashlight in each hand and point them at the same angle diagonally at the mirror in front of you, the light from one flashlight will always hit the one on the other side. This is not allowed in lithography. But if you move your hands outwards without changing the angle of the flashlights, until the centre is completely illuminated from both sides, you can reflect the light without it hitting the light from the other flashlight.”
Since the two light sources are symmetrically positioned and illuminate the mask at the same angle, on average the mask is lit from the front, which also minimizes the 3D effect on the mask.
“It’s like Columbus’ egg in that it may seem impossible at first glance, but once solved it becomes very easy,” Professor Shintake explains.
OIST has applied for a patent for this technology, and it is expected that it will be put to practical use after a demonstration experiment. “The global EUV lithography market is expected to expand from $8.9 billion in 2024 to $17.4 billion in 2030, with an average annual growth rate of about 12%. This patent has the potential to generate enormous economic benefits,” Professor Shintake sums up.
“OIST is committed to creating cutting-edge science that impacts humanity,” said Gil Granot Mayer, OIST Vice President and Leader of OIST Innovation. “This innovation embodies the OIST spirit of exploring the impossible and delivering unique solutions.”
“There is still a long way to go in developing this technology, but we are fully committed to it. We hope that this technology from Okinawa will bring about a transformation in the semiconductor industry and help solve global issues such as energy consumption and decarbonization.”
Provided by Okinawa Institute of Science and Technology Graduate University
Source: Revolutionary Extreme Ultraviolet Lithography Technology Brings Dramatic Benefits to Semiconductor Manufacturing (July 29, 2024) Retrieved July 29, 2024 from https://techxplore.com/news/2024-07-extreme-ultraviolet-lithography-technology-benefits.html
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