Extreme ultraviolet lithography (EUVL) is a promising technology for next-generation microchip fabrication. The challenge is that tin contaminates the collector mirror, which degrades the etching process. Microchip manufacturers address contamination by removing the collector and cleaning it with hydrogen plasma. But the process results in significant EUVL downtime.

Qerimi et al. developed an annular surface wave plasma (SWP) antenna technology that is integrated into the collector for in-situ tin removal. They showed that by affixing eight SWP antennas to the mirror — two to the inner cone and six to the outer perimeter — the collector is kept free from tin buildup during etching.

“Our technique could extend collector lifetimes indefinitely, expanding EUVL tool availability,” author David Ruzic said.

Extreme ultraviolet light with a 13.5 nanometer wavelength is generated by directing a carbon dioxide laser at molten tin droplets, ionizing them into a plasma for etching. The ions interact with the collector wall, causing vapor buildup. Hydrogen plasma is used to break the bonds between the tin particles and collector wall, forming gaseous tin hydride, which is removed through pumping.

The SWP antennas generate hydrogen radicals and atoms at the desired etching locations, enabling high etch rates that surpass the contamination rate by a factor of 20. The researchers found the cleaning efficiency would be even greater if the power for each antenna could be raised. They also tested the arc antenna attached to the perimeter of the collector with varying pressure and discovered plasma coverage increases at lower pressures.

“The goal is to cover every surface exposed to tin vapor with SWP,” Ruzic said.

Source: “Tin removal by an annular surface wave plasma antenna in an extreme ultraviolet source,” by Dren Qerimi, Andrew Herschberg, Gianluca Panici, Parker Hays, Tyler Pohlman and David N. Ruzic, Journal of Applied Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0094375.