In this paper, the design of an efficient illuminator for extreme ultraviolet (EUV) applications such as photolithography, metrology, and microscopy is investigated. Illuminators are arrangements of optical components that allow us to tailor optical parameters to a targeted application. For the EUV spectral range, illuminators are commonly realized by an arrangement of several multilayer mirrors. Within this publication, design methods are developed to tailor optical parameters such as the intensity distribution, the spatial coherence, and the spectral bandwidth by using only one multilayer mirror. For the demonstration of the methods, an illuminator is designed for a compact in-lab EUV interference lithography system that is suited for industrial EUV resist qualification and large-area nanopatterning. The designed illuminator increases the wafer-throughput and improves the imaging quality.
The potential of extreme ultraviolet (EUV) computational proximity lithography for fabrication of arbitrary nanoscale patterns is investigated. We propose to use a holographic mask (attenuating phase shifting mask) consisting of structures of two phase levels. This approach allows printing of arbitrary, non-periodic structures without using high-resolution imaging optics. The holographic mask is designed for a wavelength of 13.5â nm with a conventional high-resolution electron beam resist as the phase shifting medium (pixel size 50â nm). The imaging performance is evaluated by using EUV radiation with different degrees of spatial coherence. Therefore exposures on identical masks are carried out with both undulator radiation at a synchrotron facility and plasma-based radiation at a laboratory setup.
The authors present a study on the dimensional characterization of nanoscale line gratings by spectroscopic reflectometry in the extreme ultraviolet spectral range (5 nm to 20 nm wavelength). The investigated grating parameters include the line height, the line width, the sidewall angle and corner radii. The study demonstrates that the utilization of shorter wavelengths in state-of-the-art optical scatterometry provides a high sensitivity with respect to the geometrical dimensions of nanoscale gratings. Measurable contrasts are demonstrated for dimensional variations in the sub-percent regime, down to one tenth of a nanometer and one tenth of a degree in absolute terms. In an experimental validation of the method, it is shown that reflectance curves can be obtained in a stand-alone setup using the broadband emission of a discharge produced plasma as the source of EUV radiation, demonstrating the potential scalability of the method for industrial uses. Simulated reflectance curves are fit to the experimental curves by variation of the grating parameters using rigorous electromagnetic modeling. The obtained grating parameters are cross-checked by a scanning electron microscopy analysis.
Spatially resolved extreme ultraviolet reflectometry is presented in application to a local characterization of thin non-uniform contamination layers. Sample reflectivity mapping is performed, demonstrating high chemical sensitivity of the technique. Amorphous Al2O3 and carbon are determined as the contaminants of the studied silicon wafer. The results correlate with those obtained by energy-filtering photoemission electron microscopy. A laboratory tool is developed that is capable of multi-angle (2°-15°) and spectrally broadband (9.5-17 nm) extreme ultraviolet reflectometry at grazing incidence combined with a reduced sample illumination spot size, enabling spatially resolved metrology. A minimum EUV spot size of 25×30 µm in the sample plane is achieved experimentally.
In this Letter, the authors present a design study on YAG:Ce scintillator plates with a microstructured and coated surface. The goal of the study is to improve the outcoupling efficiency and to optimize the directionality of the scintillation light with respect to indirect image detection in the extreme ultraviolet spectral range (5-50 nm wavelength). In a geometric optical simulation, a gain in outcoupling efficiency by over a factor of 4 is shown while the directionality of the scintillation light is improved with respect to state-of-the-art plane scintillator plates.
We present a method for fabrication of large arrays of nano-antennas using extreme-ultraviolet (EUV) illumination. A discharge-produced plasma source generating EUV radiation around 10.88 nm wavelength is used for the illumination of a photoresist via a mask in a proximity printing setup. The method of metallic nanoantennas fabrication utilizes a bilayer photoresist and employs a lift-off process. The impact of Fresnel-diffraction of EUV light in the mask on a shape of the nanostructures has been investigated. It is shown how by the use of the same rectangular apertures in the transmission mask, antennas of various shapes can be fabricated. Using Fourier transform infrared spectroscopy, spectra of antennas reflectivity were measured and compared to FDTD simulations demonstrating good agreement.
Extreme ultraviolet (EUV) spectroscopy is a powerful tool for studying fundamental processes in plasmas as well as for spectral characterization of EUV light sources and EUV optics. However, a simultaneous measurement covering a broadband spectral range is difficult to realize. Here, we propose a method for interferometric broadband Fourier spectroscopy connecting soft x ray and visible spectral ranges with moderate spectral resolution. We present an analytical model to recover the spectrum from a double-slit interferogram. We apply our model for spectral characterization of a partially coherent gas-discharge EUV light source operated with different gases in the spectral range between 10 and 110 nm wavelengths. Our approach allows a simple and fast broadband spectroscopy with fully or partially spatially coherent light sources, for instance, to characterize out-of-band radiation in EUV lithography applications.
Fractional Talbot effect leads to the possibility to implement patterning of structures with smaller periods than the master mask. This is particularly attractive when using short wavelength illumination in the extreme ultraviolet because of attainable resolution in the sub-100-nm range. In this Letter, we demonstrate the Talbot lithography with the fractional Talbot effect under coherent illumination generated with a capillary discharge Ne-like Ar extreme ultraviolet laser. Various spatial frequency multiplications up to 5x are achieved using a parent grating. This technique allows a fabrication of nanostructures with high-resolution patterns, which is of high interest in many applications such as the manufacturing of plasmonic surfaces and photonic devices.
Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV-250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains.
