ASML’s EUV lithographs use CO₂ gas lasers as the basis for the light source. They are quite powerful, but at the same time bulky and inefficient compared to solid-state lasers. Solid-state lasers, in turn, are not very powerful and are not suitable for installation in lithographs, although they have enormous prospects in this area. China has also developed its own developments in this area, and they are no worse than those of others.
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Recently, a team from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, led by Lin Nan, former head of the Light Source Technology Department at ASML in the Netherlands, published a paper in the Chinese scientific journal Lasers on the development of a solid-state laser for the EUV light source in China. This brings China closer to developing its own EUV lithographs for the production of cutting-edge semiconductors, as the United States prohibits sales of such equipment to Chinese companies.
The conversion efficiency of CO₂ gas lasers is about 5% (only 5% of the electrical energy spent on its production is converted into light). Solid-state lasers promise to surpass this figure, and if we talk about dimensions, the comparison is not at all in favor of gas lasers: working with gas is one thing, and a compact “LED” is another. Today, semiconductor solid-state lasers are widely used for welding and other operations with metal.
For now, the power of common solid-state lasers is relatively low for lithographic production purposes — about 1 W, rarely up to 10 W. A gas laser can develop a power of up to 250 W. Nevertheless, solid-state lasers can already be used in EUV lithography — for example, to check EUV masks for defects or to assess the impact of EUV radiation on materials.
In their experiments, the Chinese team achieved a conversion efficiency of 3.42% for a 1-μm-wavelength solid-state laser. This is higher than the 3.2% achieved by a team from the Netherlands Center for Advanced Research in Nanolithography in 2019 and the 1.8% achieved by researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) in 2021.
Only American and Japanese researchers remained ahead: a group from the University of Central Florida in 2007 demonstrated a laser installation with an efficiency of 4.9%, and scientists from the Japanese Utsunomiya University with a result of 4.7%.
For comparison, the conversion efficiency of commercially available CO₂ laser-based EUV photolithography light sources is around 5.5%.