On August 2, Tsumoru Shintake, a professor at Okinawa Institute of Science and Technology Graduate University (OIST), proposed an extreme ultraviolet (EUV) lithography technology. EUV lithography technology based on this design can work with smaller EUV light sources, thereby reducing costs and significantly improving machine reliability and service life. The power consumption is less than one-tenth of that of traditional EUV lithography machines, which helps the semiconductor industry become more environmentally sustainable.
It is understood that this technology can achieve a breakthrough because it solves two problems that were previously considered insurmountable in this field. The first is a new optical projection system consisting of just two mirrors. The second is a new method of efficiently shining EUV light directly onto a logic pattern on a flat mirror (photomask) without blocking the optical path.
Manufacturing advanced semiconductor chips for artificial intelligence (AI), low-power chips for mobile devices such as cell phones, and high-density DRAM memory necessary for daily use relies on EUV lithography. However, challenges in semiconductor production include high power consumption and equipment complexity, which significantly increases the cost of installation, maintenance and power consumption. As Professor Hsinchu said, "This invention is a breakthrough technology that can almost completely solve these little-known problems."
Traditional optical systems, such as cameras, telescopes, and conventional UV lithography, have optical elements (such as apertures and lenses) axially symmetrically arranged along a central axis, which ensures the highest optical performance and minimized optical aberrations. However, this does not apply to EUV rays, as they have extremely short wavelengths, are absorbed by most materials, and cannot be transmitted through transparent lenses. Therefore, EUV light is reflected by crescent-shaped mirrors that reflect light in a zigzag pattern in open space along the optical path. However, this approach shifts light away from the central axis, sacrificing important optical properties and reducing the overall performance of the system.
The new technology achieves superior optical properties by aligning two axisymmetric mirrors with tiny central holes.
Due to the high absorptivity of EUV light, the energy is reduced by 40% each time it is reflected by a mirror. In the industry standard, only about 1% of the EUV light source energy reaches the wafer through the 10 mirrors used, which means that a very high EUV light source output is required. By comparison, by limiting the total number of mirrors from the EUV source to the wafer to four, more than 10% of the energy can be transferred, meaning that even small EUV sources outputting tens of watts can work equally efficiently, which can significantly reduce power usage.
The core projector of EUV lithography, which transfers the image on the photomask to the silicon wafer, consists of only two reflecting mirrors, similar to an astronomical telescope. This configuration is very simple, as traditional projectors require at least six reflecting mirrors. This is achieved by carefully rethinking the aberration correction theory of optics.
Professor Jun Hsinchu solved the problem by designing a new illumination optical method called "double line field", which irradiates EUV light from the front onto a plane mirror photomask without disturbing the light path.
The Okinawa Institute of Science and Technology has applied for a patent for this technology and is expected to put it into practical use through demonstration experiments. The global EUV lithography market is expected to grow from US$8.9 billion in 2024 to US$17.4 billion in 2030, with an average annual growth rate of 12%, and this patent is expected to generate huge economic benefits.