Extreme Ultraviolet Light Sources for Nanolithography

Extreme ultraviolet (EUV) lithography relies on sources emitting around 13.5 nm to pattern features at the sub-10 nm scale in semiconductor manufacturing. The prevailing approach utilises laser-produced plasma (LPP) generated by irradiating molten tin microdroplets, which convert laser energy into EUV emission. Industrial systems most often employ CO₂ lasers to optimise target shaping and achieve stable high-power output, while emerging developments explore solid-state lasers at 1 µm and 2 µm wavelengths to enhance wall-plug efficiency and throughput. Key challenges include maximising conversion efficiency (CE) of laser energy to EUV radiation, managing debris and target replenishment, and engineering multilayer mirror coatings to reflect the narrow spectral band. Progress in understanding plasma dynamics—from nanosecond-scale ionisation and opacity effects to microsecond-scale fluid-dynamic expansion—and in refining laser-target interaction strategies has underpinned steady gains in source brightness, stability and industrial viability.

Research from Nature Portfolio

Recent studies have mapped two-dimensional plasma inflow in tin LPP, using collective Thomson scattering to reveal ultrafast flows exceeding 10⁴ m/s toward the plasma axis. Time-resolved profiles of electron density, temperature and charge state demonstrated how controlled plasma circulation sustains optimal conditions for EUV generation over extended intervals, offering routes to improve overall light output.

Investigations into tin opacity spectra have elucidated the atomic origins of EUV emission, showing that transitions between multiply-excited states dominate the narrow 13.5 nm window rather than solely those from singly excited levels. This insight overturns earlier paradigms, providing a more accurate framework for atomic modelling and guiding the design of plasma conditions to enhance spectral brightness.

Extreme Ultraviolet Light Sources for Nanolithography publication trend

The graph below shows the total number of articles in extreme ultraviolet light sources for nanolithography across all publications each year (not limited to Nature Index journals).

Technical terms

Extreme Ultraviolet (EUV): Electromagnetic radiation in the 10–14 nm wavelength range used for high-resolution lithography.

Laser-Produced Plasma (LPP): A dense, hot plasma generated by intense laser irradiation of a target, serving as an EUV light source.

Conversion Efficiency (CE): The fraction of input laser energy converted into usable EUV radiation within a specified spectral band.

Collective Thomson Scattering: A diagnostic technique for measuring plasma parameters by analysing scattered laser light from free electrons and ions.

Multilayer Optics: Mirror coatings composed of alternating layers of different materials, designed to reflect EUV light at specific wavelengths with high efficiency.

References

1. Physics of laser-driven tin plasma sources of EUV radiation for nanolithography. Plasma Sources Science and Technology (2019).
2. Microdroplet-tin plasma sources of EUV radiation driven by solid-state-lasers (Topical Review). Journal of Optics (2022).
3. Observation of plasma inflows in laser-produced Sn plasma and their contribution to extreme-ultraviolet light output enhancement. Scientific Reports (2023).
4. Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources. Scientific Reports (2017).
5. Prominent radiative contributions from multiply-excited states in laser-produced tin plasma for nanolithography. Nature Communications (2020).
6. Mass Partitioning in Fragmenting Tin Sheets. Physical Review Applied (2023).
7. Scaling relations in laser-induced vaporization of thin free-flying liquid metal sheets. Physical Review Research (2024).
8. Extreme ultraviolet light from a tin plasma driven by a 2-µm-wavelength laser.. Optics Express (2021).