High-frequency gyrotron and microwaves yield first extreme ultraviolet radiation

Developing high-resolution projection lithography for microelectronics chips demands powerful and reliable sources of light emitted at a narrow set of extreme ultraviolet (EUV) wavelengths. Current approaches using laser plasma are approaching the upper limit of their operational capacity. As attempts are made to safely and effectively create such conditions, new work with noble gases and microwaves looks to help provide the multi-kilowatt output power levels required for next-generation chip production.

Shalashov et al. demonstrated the possibility of generating extreme ultraviolet radiation with a jet of dense plasma supported by high-power microwaves. They used a state-of-the-art, 250-gigahertz gyrotron to produce the microwave radiation and subsequent plasma with multi-charged ions, which operated with unique characteristics of 250-kW output power in 50-microsecond pulses. With a sufficient power supply, the gyrotron could also support continuous wave operation.

“A key physical problem for a EUV light source is producing of multiply charged ions and keeping them in place,” said Shalashov. “Compared to existing devices with laser-produced plasma, our scheme is featured with a relatively simple design, a safe operation for EUV optics, and a possibility of continuous-wave operation.”

The authors state that their discharge reached a peak electron density of up to 3 × 10¹⁷ electrons per cubic centimeter and a size of 150 micrometers when supported by the focused radiation of the gyrotron. These characteristics make the technique a viable candidate as a simpler EUV source for industrial-scale applications like high-resolution lithography.

The authors report a new theoretical model that allows them to interpret the measurements and plan further experiments where they hope to improve efficiency by incorporating a 670-gigahertz gyrotron, and one day scale the technology for use in microelectronics.

Source: “Observation of extreme ultraviolet light emission from an expanding plasma jet with multiply charged argon or xenon ions,” by A. G. Shalashov, A. V. Vodopyanov, I. S. Abramov, A. V. Sidorov, E. D. Gospodchikov, S. V. Razin, N. I. Chkhalo, N. N. Salashchenko, M. Yu. Glyavin, and S. V. Golubev, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5049126 .