Decades of cutting-edge laser, optics and plasma physics research at Lawrence Livermore National Laboratory (LLNL) played a key role in the underlying science that the semiconductor industry uses to manufacture advanced microprocessors. These computer chips drive today's astounding innovations in artificial intelligence, high-performance supercomputers and smart phones.
Now a new research partnership led by LLNL aims to lay the groundwork for the next evolution of extreme ultraviolet (EUV) lithography, centered around a Lab-developed driver system dubbed the Big Aperture Thulium (BAT) laser.
The team will participate in the Extreme Lithography & Materials Innovation Center (ELMIC), one of the centers selected for the Department of Energy (DOE) Office of Science's Microelectronics Science Research Centers (MSRCs). The DOE announced $179 million in funding for the three MSRCs, which were authorized as part of the bipartisan CHIPS and Science Act of 2022.
ELMIC aims to advance the basic science driving the integration of new materials and processes into future microelectronic systems. The LLNL-led project within this center is a four-year, $12 million investigation specifically aimed at expanding the fundamental science around EUV generation and plasma-based particle sources. Other ELMIC projects will focus on key research areas such as plasma-based nanofabrication, 2D-material systems and extreme-scale memory.
The LLNL-led project will test the BAT laser's ability to increase EUV source efficiency by about 10 times when compared with carbon dioxide (CO2) lasers, the current industry standard. This could lead to a next generation "beyond EUV" lithography system producing chips that are smaller, more powerful and faster to manufacture while using less electricity.
"We have performed the theoretical plasma simulations and proof of concept laser demonstrations over the past five years that lay the foundations for this project," said LLNL laser physicist Brendan Reagan. "Our work has already had quite an impact in the EUV lithography community, so now we're excited to take this next step."
Reagan and LLNL plasma physicist Jackson Williams are the project's co-lead principal investigators. The project includes scientists from SLAC National Accelerator Laboratory; ASML San Diego; and the Advanced Research Center for Nanolithography (ARCNL), a public-private research center based in the Netherlands.
EUV lithography involves high-power lasers firing at tens of thousands of droplets of tin per second. The laser heats the droplets, each measuring about 30 millionths of a meter, to half a million degrees centigrade to produce a plasma that generates ultraviolet light with a wavelength of 13.5 nanometers.
Special multi-layer mirrors guide the light through plates called masks, which hold the intricate patterns of the integrated circuits for semiconductor wafers. The light projects the pattern onto a photoresist layer that is etched away to leave the integrated circuits on the chip.
The LLNL-led project will investigate the primary hypothesis that energy efficiency of existing EUV lithography sources for semiconductor production can be improved with technology developed for the novel petawatt-class BAT laser, which uses thulium-doped yttrium lithium fluoride as the gain medium through which the power and intensity of laser beams are increased.
The unique central wavelength of thulium-doped yttrium lithium fluoride, lasing at about 2 microns, differs from all other intense lasers that operate at about or less than 1 micron or at 10 microns. The project will be the first exploration of joule-class laser-target coupling at 2 microns.
This builds on the work made possible by internal investments from LLNL's Laboratory Directed Research and Development Program as well as externally funded support from the DOE Office of Science's Office of High Energy Physics Accelerator Stewardship Program, and the Defense Advanced Research Projects Agency.
The researchers plan to demonstrate pairing the compact high-rep-rate BAT laser with technologies that generate sources of EUV light using shaped nanosecond pulses and high-energy X-rays and particles using ultrashort sub-picosecond pulses.
"This project will establish the first high-power, high-repetition-rate, about 2-micron laser at LLNL," Williams said. "The capabilities enabled by the BAT laser also will make a significant impact on the fields of high energy density physics and inertial fusion energy."
Many of the experiments will be performed at the Jupiter Laser Facility (JLF) at LLNL. JLF is a mid-scale user facility, which just completed a four-year-long refurbishment, and is a member of LaserNetUS, a DOE Office of Science Fusion Energy Sciences network of high power laser facilities in North America.
Since its inception, the semiconductor industry has engaged in a constant race to make each generation of microprocessors smaller yet more powerful by packing as many integrated circuits and other features as possible into one chip. For the past several years, EUV lithography has taken the forefront because it uses EUV light to etch microscopic circuits as small as a few nanometers onto advanced chips and processors.
Reagan noted that the Lab has long pioneered the development of EUV lithography, including early spectroscopic studies that formed the foundation of plasma-based EUV sources.
A 1997 cooperative research project involving LLNL, Sandia National Laboratories and Lawrence Berkeley National Laboratory led to the development of the Engineering Test Stand, the first prototype EUV exposure tool.
Furthermore, the Lab developed efficient multilayer optics that are instrumental in transporting and delivering the EUV light for lithography. Previously, LLNL partnered with ASML to exploit the Lab's extensive plasma simulation capabilities to optimize source efficiency.
Over the years, LLNL's extensive multidisciplinary research contributed to multilayer coating science and technology, optics metrology, light sources, lasers, high-performance computing and, notably, the historic achievement of fusion ignition at NIF in December 2022.
ASML, which makes the EUV lithography machines used by the biggest commercial producers of these chips, uses CO2 pulsed lasers to drive the EUV light sources. But LLNL research over the past decade showed that newer diode-driven solid-state laser technology provides a promising path toward achieving higher power and greater overall efficiency for EUV lithography systems.
In addition to Reagan and Williams, key members of LLNL's multidisciplinary team include Félicie Albert, Leily Kiani, Emily Link, Thomas Spinka, Issa Tamer and Scott Wilks.
The project also includes Siegfried Glenzer, SLAC's high energy density division director and a former LLNL plasma physics group leader, Michael Purvis, ASML's lead EUV source research technologist and Oscar Versolato, head of the source department at ARCNL.
-Benny Evangelista
