Extreme Ultra-Violet and Its Applications

    EUV refers to Extreme Ultra-Violet with a wavelength of 13.5 nm. Also called soft X-rays. EUV exposure technology using extreme ultraviolet light is expected as a new generation of exposure technology that can further miniaturize semiconductors.

    The previous semiconductor exposure technique was to increase the resolution at the time of exposure by shortening the wavelength of the light used to satisfy the need for miniaturization. However, in the past 10 years, the exposure wavelength has remained unchanged at 193 nm. The reason is that the industry has introduced a liquid immersion exposure technique in which water is filled between the lens and the wafer, and a double exposure technique such as repeated exposure, instead of shortening the wavelength to increase the resolution.

Remarkably shorten the exposure wavelength

EUV exposure shortens the exposure wavelength to 13.5 nm, thereby increasing the resolution at the time of exposure. (This image was produced by Nikkei Electronics based on information from International Technology Roadmap for Semiconductors (ITRS). Photo courtesy of Asimah.)

    However, these technologies are also getting closer to the limit. The latest immersion exposure technology has a resolution of about 38 nm, and 19 nm is the limit even with the use of a secondary pattern exposure technique. If you continue to increase the resolution, you need to increase the number of exposures to more than 3 times, which will increase costs. With the EUV exposure technology with a wavelength of only 13.5 nm, a pattern of about 14 nm can easily be formed in one exposure.

    However, the development of EUV exposure technology is becoming slower and slower. The main reason is that the output power of the EUV light source is currently only 10 to 20 W, which is still far from the 250 W required for mass production. If this goes on, it will have a huge impact on the pace of semiconductor miniaturization. Therefore, ASML, which is engaged in the EUV exposure equipment business, announced in October 2012 that it will acquire Cymer, the world's largest manufacturer of EUV light sources, to accelerate development. Asmar's goal is to achieve the required 250W of output power of EUV light source in 2015.

   Extreme ultraviolet photolithography (EUV) may be considered as one of the most promising technologies. Although there are still many technologies currently waiting to be overcome.

   The semiconductor industry is adopting two graphic exposure technologies and is envisaging a gradual transition to EUV technology. Therefore, until 2012, the advanced technology will use twice the graphics exposure technology at the 22nm half pitch as the mainstream. Among the respondents, 60.4% of users believe that two pattern exposure techniques will be used in gate layer lithography and 51.1% are considered to be used in contact layer lithography. However, by 2014-2015 many respondents believed that by the time of the 16nm era, 43% of the respondents believed that it might be applied in gate layer manufacturing and 47.7% were used in contact layer lithography. By the time of 2016-2018, many people in the industry believed that it would enter 11nm, when 60.6% of respondents believed that it might be applied to the lithography of the photolithography layer and 63.9% of them were used in contact layer lithography.