EUV Lithography Science
CXRO: A Pioneer and Leader in EUV Lithography Research
Extreme ultraviolet (EUV) lithography is currently used to print the most advanced microelectronics chips (at the 2 nm and 3 nm nodes). It uses light at λ = 13.5 nm to achieve resolution down to 7.5 nm (half-pitch) when a high numerical aperture (NA) is used.
For over 20 years, CXRO has been leading the research on EUV lithography through its work on imaging and photoresist science using projection lithography instruments of increasing resolution capability (wmin ≈ 0.25 λ/NA), as illustrated below.
0.1 NA Sub-field Exposure Station (SES)
wmin ≈ 34 nm
[Naulleau et al.]
0.3 NA Micro-Exposure Tool (MET3)
wmin ≈ 11 nm
[Naulleau et al.]
Toward Hyper-NA
As high-NA EUV lithography is now being inserted in industrial production of the most advanced microelectronics chips, CXRO has started to prepare for the next generations of EUV lithography, actively working with industry and the U.S. government to establish a new research platform with a numerical aperture of NA = 0.75, dubbed hyper-NA, capable of resolving a half-pitch of 4.5 nm. A schematic of the concept is shown below.
The Center is also developing an EUV interference lithography tool that will support the national research effort on EUV and beyond-EUV lithography, in collaboration with the Center for Functional Nanomaterials (CFN) at Brookhaven National Laboratory.
Key Research Areas
Stochastic Patterning
At EUV wavelengths, the small number of photons per resolution element introduces statistical fluctuations (shot noise) that cause line-edge roughness, stochastic defects, and CD variability. CXRO research develops models and experiments to quantify and mitigate these effects.
Aerial Image Formation
Understanding how the aerial image is formed by EUV optics — including the roles of pupil fill, mask topography (3D mask effects), and optical aberrations — is critical for predicting patterning performance.
Mask 3D Effects
EUV masks are reflective multilayer structures. The finite thickness of the absorber and the oblique illumination angle create shadowing and phase effects that shift and distort the printed image. CXRO characterizes these effects experimentally using SHARP and computationally through rigorous simulations.
High-NA EUV
Next-generation high-NA (0.55) EUV systems introduce new challenges including anamorphic imaging, increased sensitivity to polarization, and tighter overlay budgets. CXRO research supports the scientific foundation for this transition.
Related Capabilities
This research is closely supported by the MET (Micro-Exposure Tool) for printing experiments and the SHARP microscope for actinic mask imaging.