Serhiy Danylyuk

Optimization of a gas discharge plasma source for extreme ultraviolet interference lithography at a wavelength of 11 nm

In this work, we report about the optimization of the spectral emission characteristic of a gas discharge plasma source for high-resolution extreme ultraviolet (EUV) interference lithography based on achromatic Talbot self-imaging. The working parameters of the source are optimized to achieve a required narrowband emission spectrum and to fulfill the necessary coherence and intensity requirements. The intense 4f-4d transitions around 11 nm in a highly ionized (Xe8+–Xe12+) xenon plasma are chosen to provide the working wavelength. This allows us to increase the available radiation intensity in comparison with an in-band EUV xenon emission at 13.5 nm and opens up the possibility to strongly suppress the influence of the 5p-4d transitions at wavelengths between 12 and 16 nm utilizing a significant difference in conditions for optical thickness between 4f-4d and 5p-4d transitions. The effect is achieved by using the admixture of argon to the pinch plasma, which allows keeping the plasma parameters approximate...

Scalability limits of Talbot lithography with plasma-based extreme ultraviolet sources

Abstract. Lithography has been faced with a challenge to bring resolution down to the 10-nm level. One of the promising approaches for such ultra-high-resolution printing is self-imaging Talbot lithography with extreme ultraviolet (EUV) radiation. However, as the size of structures on the mask approaches the wavelength of the radiation, diffraction influence needs to be evaluated precisely to estimate the achievable resolution and quality of the patterns. Here, the results of finite-difference time-domain simulations of the diffraction on EUV transmission masks in dependence to the period (pitch) of the mask are presented with the aim to determine the resolution that can be realistically achieved with the EUV Talbot lithography. The modeled experimental setup is utilizing partially coherent EUV radiation with the wavelength of 10.9 nm from Xe/Ar discharge plasma EUV source and Ni/Nb-based amplitude transmission mask. The results demonstrate that the method can be used to produce patterns with resolution down to 7.5-nm half-pitch with 2∶1 mask demagnification utilizing achromatic Talbot effect and transverse electric (TE)-polarized light.

Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies

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.

Diffraction-assisted extreme ultraviolet proximity lithography for fabrication of nanophotonic arrays

In this article, the possibilities and limitations of proximity lithography with extreme ultraviolet (EUV) radiation are explored theoretically and experimentally. Utilizing partially coherent EUV radiation with a wavelength of 10.88 nm from a Xe/Ar discharge plasma EUV source, proximity patterning of various nanoantenna arrays has been performed. The experimental results are compared with the results of numerical scalar diffraction simulations, and it is shown that proximity printing in the Fresnel diffraction mode can enable production of high-resolution features even with lower resolution masks, successfully demonstrating sub-30 nm edge resolution in the resist. The potential of the method is explored by simulation of the patterning through circular and triangular apertures as well as through bowtie antenna patterns, with the results suggesting that precise control of the proximity gap and the exposure dose together with simulation-supported mask design optimizations may allow for a wide variety of high-resolution structures to be printed through relatively simple transmission masks. The method is especially suited for high-performance manufacturing of submicrometer sized nanophotonic arrays.

Fractional Talbot lithography with extreme ultraviolet light

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.

Interferometric broadband Fourier spectroscopy with a partially coherent gas-discharge extreme ultraviolet light source

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.

Optical properties of 2D fractional Talbot patterns under coherent EUV illumination

We investigate optical properties of (2D) fractional Talbot patterns under illumination with EUV laser light. The fractional Talbot effect, due to spatial frequency multiplication, can enable patterning of micro and nano-structures with various feature sizes using a micro-scale pitch mask. The experiment is performed with a free-standing mask fabricated by focused ion beam milling and a highly coherent illumination at 46.9 nm wavelength generated by a compact capillary discharge Ne-like Argon laser. As a result of spatial frequency multiplication, structure density of a square array of apertures in the mask was increased by a factor of up to 9 at the recording plane. The depth of field of the fractional Talbot images has been investigated using Fresnel diffraction analysis. Added field distribution complexity caused by asymmetry of the 2D arrays was observed both in simulation and in the experiment. This approach could be useful for sub-micron structuring of 2D patterns for various applications including among others the fabrication of photonic crystals, quantum dots, and also of submicron-electronic devices.

Extreme ultraviolet proximity lithography for fast, flexible and parallel fabrication of infrared antennas

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.

Achromatic Talbot lithography with partially coherent extreme ultraviolet radiation: process window analysis

Abstract. The main purpose of this work is the experimental determination of the process window for achromatic Talbot lithography with partially coherent extreme ultraviolet (EUV) radiation. This work has been performed using the EUV laboratory exposure tool. It consists of a discharge produced plasma source with a direct beam path to a phase-shifting transmission mask, avoiding losses due to additional optical components, the photoresist-coated wafer, and a positioning system for each component. Both the source and the mask are optimized for 11-nm wavelength. The process window has been identified by a systematic analysis of several exposure series. The optimization of exposure parameters resulted in 50-nm half-pitch of the wafer features using a transmission mask with a rectangular dot array of 70-nm half-pitch. The depth of field is found to be 20  μm, and it can be extended by spatial filtering. The exposure dose and mask–wafer distance are varied around their optimal values to estimate the process window, using defectivity of the pattern as a control parameter.

Tabletop coherent diffraction imaging with a discharge plasma EUV source

We present a coherent diffraction imaging (CDI) experiment using a high-frequency discharge plasma based, extreme ultraviolet (EUV) source. By using different illumination geometries, we generated EUV beams witha varying degree of spatial coherence, which were used to produce far field diffraction patterns from test objects. We then successfully reconstructed an illumination wavefront defined by a circular aperture. The present work explores the feasibility of compact tabletop CDI using a discharge plasma EUV source emerged from the technology development of EUV lithography, which can potentially find application in nanoscience and metrology.