TEUS-S100 EUV LPP (laser-produced plasma) source

2021

Partners
EUV Labs, Ltd.,
Institute for Spectroscopy RAS
ISTEQ B.V.
TEUS-S100 is a high-brightness EUV LPP light source with a low amount of plasma debris to be used in metrology for microchip production.
Challenge
The method of EUV lithography based on plasma light sources with a wavelength of 13.5 nm is used to high volume manufacturing the new-generation microchips with the technological node of 3−5 nm.


Purity control and quality verification of lithographic masks for such microchips requires a source with precisely the same wavelength as for production (actinic radiation), yet more compact, with high brightness and stability, not requiring complex infrastructure and not producing plasma debris. Many research teams and commercial companies around the world are involved in studying this problem. The EUV Labs specialists developed and patented the fundamental concept of such a actinic source while our task was to proceed from the principle and laboratory prototype to a commercial serial device for the most high-tech industry in the world. Finally, we did construct such a device.
Solution
At the heart of the EUV source, there is a disk rotating in a vacuum and covered with a thin film of molten tin. This film is the target for a powerful pulsed laser "shooting" into it at a high frequency and converting it into plasma that re-emits at a wavelength of 13.5 nm.

Fast rotation of the disk has a critical role: first, it clears the radiation collection site of plasma debris, and second, it constantly updates the target material providing undisturbed target surface, thereby ensuring spatial stability of the radiation and allowing the use of a high-frequency laser. During the disk rotation, tin droplets, ions, and clusters move along the inertia of the disk and do not reach the exit window or collector mirror of the EUV radiation.
plasma EUV source by TRDC scheme
The disk should rotate in a vacuum at 12,000 revolutions per minute to produce the desired effect. We selected special composite bearings with ceramic balls capable of such speeds: ordinary steel ones could not cope with such conditions. To prevent bearing grease fumes from contaminating the working volume of the vacuum chamber, we selected a special grease used in spacecrafts.

There being no thermal conductivity in a vacuum, everything heated in the unit’s volume has to be forcedly cooled in a special way. At the same time, there should be no more than 60°C in the center of the disk to ensure proper operation of the bearings, the outer surface should be molten tin at about 300°C, and the temperature of the emitting EUV plasma, in general, is close to a million degrees. Our engineers selected a special titanium alloy for the disk and calculated its shape to provide the necessary strength and thermal conductivity.
A special challenge is how to remove heat from the disk. The laser, with a capacity of several hundred watts, shoots directly into the disk, with all the heat being released on it, accordingly.
We created a labyrinth cooling system under the disk that removes heat through a small gas flow and transfers it to the cooling plate. A turbomolecular pump maintains the vacuum in the system and pumps out the cooling gas.

For this setup, we also designed and manufactured many auxiliary systems: disc contactless vacuum preheater, cooling, vacuum and its control, gases, heat exchangers, electrics, automatics to control and maintain operating modes…
Result
A commercially available actinic light source for inspection of lithographic masks and optics at 13.5 nm that is bright, clean, and maintenance free.

The device is manufactured on request.
Team
Distributor
Media
Other innovative products designed by TRDC