Breakthrough in EUV Lithography Technology by OIST Professor
On August 2, Professor Tsumoru Shintake from the Okinawa Institute of Science and Technology Graduate University (OIST) proposed an Extreme Ultra-Violet (EUV) lithography technology. This EUV lithography technology based on this design can work with a smaller EUV light source, reducing costs and significantly improving the reliability and service life of the machine. And it consumes less than one-tenth of the power of traditional EUV lithography machines, helping the semiconductor industry become more environmentally sustainable.
It is understood that this technology can achieve a breakthrough because it solves two previously considered insurmountable problems in this field. The first is a new optical projection system composed of only two mirrors. The second is a new method to efficiently irradiate the EUV light directly onto the logical pattern on the plane mirror (photomask) without blocking the optical path.
Manufacturing advanced semiconductor chips for low-power chips used in artificial intelligence (AI) and mobile devices such as mobile phones, as well as high-density DRAM memory necessary for daily life, all rely on EUV lithography technology. However, the challenges faced in semiconductor production include high power consumption and the complexity of equipment, which significantly increases the cost of installation, maintenance, and power consumption. As Professor Shintake said, 'This invention is a breakthrough technology that can almost completely solve these little-known problems.'
In traditional optical systems, such as cameras, telescopes, and regular ultraviolet lithography, their optical elements (such as diaphragms and lenses) are arranged axially symmetrically along the central axis, which ensures the highest optical performance and minimizes optical aberrations. However, this is not applicable to EUV rays because their wavelengths are extremely short and are absorbed by most materials and cannot propagate through transparent lenses. Therefore, EUV light is reflected by crescent-shaped mirrors that reflect light in a zigzag pattern along the optical path in open space. However, this method deflects the light from the central axis, sacrificing important optical characteristics and reducing the overall performance of the system.
This new technology achieves superior optical characteristics by aligning two axially symmetric mirrors with tiny central holes in a straight line.
Due to the high absorptivity of EUV light, the energy will be weakened 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 a very high EUV light source output is required. In contrast, 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, which means that even a small EUV source with an output of several tens of watts can work equally effectively, 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 because traditional projectors require at least six reflecting mirrors. This is achieved by carefully rethinking the aberration correction theory of optics.
Professor Shintake solved the problem by designing a new illumination optical method called 'two-line field', which irradiates the EUV light to the plane mirror photomask from the front without interfering with the optical path.
The Okinawa Institute of Science and Technology Graduate University has applied for a patent for this technology and is expected to be put into practical use through demonstration experiments. The global EUV lithography market is expected to grow from $8.9 billion in 2024 to $17.4 billion in 2030, with an average annual growth rate of 12%, and this patent is expected to generate huge economic benefits.