A carbon nanotube–based pellicle for EUV lithography. [Image: Courtesy of imec]
The Belgian nanoelectronics innovation hub imec and the Japan-based chemical company Mitsui Chemicals have announced a strategic partnership to commercialize a key component for next-gen systems for extreme-ultraviolet (EUV) semiconductor lithography.
The partnership focuses on EUV pellicles—thin, transparent membranes that protect the EUV photomask from potentially catastrophic contamination during production. The imec–Mitsui partnership is designed to bring new pellicle designs based on carbon nanotubes to commercial production in the 2025–26 time frame, in sync with plans to boost the power of EUV lithography light sources.
Pellicle protection
EUV lithography has exploded with the need to pack ever-more features at ever-smaller scales onto semiconductor integrated circuits—and thereby keep Moore’s law working for as long as possible. The EUV lithography equipment market is largely owned by the Dutch behemoth ASML, which produces and sells advanced, intricate machines that produce 13.5-nm EUV light by firing repeated CO2-laser pulses onto droplets of molten tin to create a plasma that radiates at EUV wavelengths. The EUV radiation is then shunted via specialized optics to a scanner for lithographic patterning at nanometer-scale dimensions. (For more on how these remarkable machines work, see “EUV Light Sources for Next-Gen Lithography,” OPN, March 2018.)
The super-small size of the features carved by these light sources raises the stakes for protecting the very expensive photomasks used in the EUV space—each of which, for some applications, can cost hundreds of thousands of US dollars—from contamination by stray particles. In actual production, such contamination can seriously impact yields. EUV pellicles, which are mostly transparent to EUV light, are laid atop the photomask to provide the needed protection.
The partnership focuses on EUV pellicles—thin, transparent membranes that protect the EUV photomask from potentially catastrophic contamination during production.
Until a few years ago, ASML itself was the sole supplier of EUV pellicles, but it has recently transferred assembly and production of these membranes to Mitsui Chemicals. Selected other suppliers also market pellicles for EUV lithography end users.
CNT-based technology
The imec–Mitsui partnership is designed to create pellicles tuned to the next generation of EUV light source technology, which is road-mapped for powers exceeding 600 W by 2025–26 to enable higher-quality nanoscale lithography. The pellicle technology the organizations will target uses carbon-nanotube (CNT) technology to improve performance of the membranes.
According to a press release from imec and Mitsui, the CNT-based pellicles transmit greater than 94% of EUV light with very low EUV reflectance, and can withstand EUV power levels beyond 1000 W. CNT-based pellicles are also physically strong, and are transparent not only to the EUV light used for actual lithography but also to the deep-ultraviolet (DUV) wavelengths used in some systems for inspection and quality control of lithography results.
“Strong interest” seen
Under the joint arrangement, according to the release, Mitsui will “integrate imec’s fundamental CNT-based pellicle innovation into Mitsui Chemicals’ CNT pellicle technology to achieve full production specifications” in time for the transition to higher-power EUV systems in the 2025–26 timeframe. The partnership will include “consultation and EUV scanner validation by imec for commercialization at Mitsui Chemicals.” Mitsui and imec say the properties of CNT-based pellicles “have generated strong interest from companies that use EUV lithography in high-volume manufacturing.”
Imec—which has been working to advance the capabilities of CNT-based pellicles for years—is “confident that the in-depth knowledge we have on the metrology, characterization, properties and performance of CNT membranes will accelerate Mitsui Chemicals’ product development,” said Steven Scheer, an imec senior vice president, in the imec–Mitsui press release. “Together, we hope to bring CNT pellicles into production for future generations of EUV lithography.”