High-efficiency diffraction gratings for EUV and soft x-rays using spin-on-carbon underlayers

Abstract

We report on the fabrication and characterization of high-resolution gratings with high efficiency in the extreme ultraviolet (EUV) and soft x-ray ranges using spin-on-carbon (SOC) underlayers. We demonstrate the fabrication of diffraction gratings down to 20 nm half-pitch (HP) on Si3N4 membranes with a bilayer of hydrogen silsesquioxane (HSQ) and spin-on-carbon and show their performance as a grating mask for extreme ultraviolet interference lithography (EUV-IL). High-resolution patterning of HSQ is possible only for thin films due to pattern collapse. The combination of this high-resolution resist with SOC circumvents this problem and enables the fabrication of high aspect ratio nanostructures. Rigorous coupled-wave analysis shows that the bilayer gratings exhibit higher diffraction efficiency than what is feasible with a grating made of HSQ. We also demonstrate a simple and accurate method to experimentally measure the diffraction efficiency of high-resolution gratings by measuring the relative ratio of the dose-to-clear curves of the photoresist. The measured diffraction efficiencies are in good agreement with the theoretically predicted values. Furthermore, we verify our calculations and measurements by printing line/space patterns in chemically amplified resists down to 10 nm HP with both HSQ and bilayer grating masks using EUV-IL. The improved diffraction efficiency of the bilayers is expected to have applications not only in gratings for interference lithography, but also in Fresnel zone plates and gratings for spectroscopy in the EUV and soft x-ray ranges.

Sub-Nanometer Line Edge Roughness in Helium-ion Lithography

“…Importantly, a reduced resist thickness offers a wider dosage range for manufacturing nanostructures with subnanometer LER. By employing SHIBL on suspended thin films, the fabrication of diffraction grating structures with LER below 0.4 nm has been realized 22,35 . These gratings, when utilized in EUV interference lithography (EUV-IL) mask fabrication endeavors, improve the diffraction efficiency of EUV-IL, increase the spatial energy contrast during exposure, and enhance the experimental traceability in the evaluation of EUV resists.…”

The EUV lithography resist screening activities in H2-2022

“…The fabrication process of such gratings has been reported elsewhere. 8 The two diffracted beams are designed to interfere on the resist surface and create periodic L/S patterns, as shown in Figure 1. The intensity distribution of the aerial image is determined by the constructive and destructive interference of the two diffracted beams, given by…”

Advancements in EUV photoresists for high-NA lithography

“…The XIL beamline and our EUV-IL technique have been previously described elsewhere in detail. 7 Briefly, EUV light is diffracted by two or more identical transmission gratings on a thin silicon nitride membrane 8 and the mutually coherent diffracted beams interfere, creating a periodic aerial image. In our work, we have used masks with two gratings which create highresolution line/space (L/S) patterns.…”