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The research presented in this thesis concerns brittle fracture of free-standing nanoscale thin films, specifically transition metal silicide films which have found use in EUV pellicles. Ensuring the reliability of thin film EUV pellicles requires an understanding of the mechanical properties of the thin film material, which can significantly differ from the properties of its bulk counterpart due to scale effects and differences in the microstructure. The first half of the work aims to deepen the understanding of the link between composition, structure, and fracture strength in transition metal silicide thin films. With this goal, an experimental investigation was carried out using a combination of mechanical characterization techniques, membrane bulge test and tensile testing, with X-ray diffraction and transmission electron microscopy. The second half of the work moves its focus from fracture strength toward another important mechanical property – resistance to crack propagation, or fracture toughness. The recently developed crack-on-a-chip test method was successfully adapted for metal silicide thin films to determine their fracture toughness. Furthermore, several improvements have been made to the method, such as the addition of on-chip drawbridge-like actuators and taking into account the effect of buckling in the analysis, which enable a more detailed and accurate characterization of the fracture process.

This work is dedicated to thin film reflective multilayer optics working in the range between the O Ka and the Al Ka absorption edges (525 eV-1486 eV) to be used in spectroscopic applications. The main requirements for multilayer optics in spectroscopy are a high peak reflectance and a narrow bandwidth. The periodicity of the multilayer system designed for such an energy range is only 2.5 nm with individual layers being thinner than 1 nm. This makes the performance of such systems extremely sensitive to any imperfection at the interfaces. Analysis of such short period structures is very challenging due to the limitations of conventional methods that are commonly used for multilayer systems with larger periodicities. Therefore, this research faced two main challenges: engineering and analysis. In the engineering part, to improve the optical contrast and the quality of the interfaces various techniques such as ion beam polishing of layers, alternative working gas, and the use of alternative material combinations were applied. The analysis part required a combination of several state-of-the-art analytical methods in order to obtain reliable information about interfaces and film growth. A comprehensive analysis of the short-period W/Si and W/B multilayer systems was carried out in this work. A combination of various state-of-the-art analysis techniques was used to obtain reliable information about the internal structure of the multilayers. Understanding the physics of thin-film growth at the atomic scale helped to define the next steps in improving the performance of such systems as discussed in the "valorization and outlook" section. This thesis is a basis for further studies on this type of multilayer mirrors.

This PhD thesis contains a selection of thin film research results on the structure control of La/B multilayer mirrors with nm- and sub nm-thick layers, used at normal and grazing incidence of XUV radiation. Topics investigated include an improvement of the optical layer contrast, the reflectivity at 6.x nm wavelength, and the thermal stability. The approaches presented deal with in situ growth studies, deposition control and high resolution X-ray analysis.

In this thesis we describe the development of a new class of optical components to enhance the imaging performance by enabling adaptations of the optics. When used at extreme ultraviolet (EUV) wavelengths, such ‘adaptive optics’ offers the potential to achieve the highest spatial resolution in imaging known to date, i.e., a resolution down to several nanometers. These optics are discussed, e.g., in the field of photolithography for the fabrication of more energy efficient and faster electronic equipment. The topics in this thesis can be subdivided into two parts. The first part includes a mirror design that can be used to enhance the spectral quality of EUV light sources. Our design consists of a diffractive Fresnel zone plate patterned in the surface of a curved mirror to achieve spectral purification, i.e., removing undesired wavelengths of the EUV light sources. The removed light is recycled to produce more EUV light. This design achieves four orders of magnitude purification and provides a 35% improvement in efficiency. The second part of the thesis describes a new class of adaptive multilayer mirrors that can be used to correct wavefront distortions, reflectance degradations or wavelength deviations. These adaptive optics contain integrated crystalline piezoelectric thin films of which the film thickness can be adjusted by an externally applied voltage. Because the optics substrates typically have an amorphous structure, so far it was not possible to grow high quality crystalline piezoelectric films on them. We utilized crystalline nanosheets on these substrates to grow the highest quality, i.e., epitaxial, piezoelectric films (PbZr0.52Ti0.48O3, PZT). The PZT films show a record high piezoelectric coefficient of 98 pm/V, although the piezoelectric response in this case is still reduced due to clamping by the substrate. We minimized the clamping effect by depositing films with a columnar structure, which enhances the voltage-controlled change in film thickness. In these films we measured a piezoelectric response of 280 pm/V, the highest value reported on glass substrates. Importantly, the developed films can produce a stroke of 25 nm. This order of magnitude is useful when considering to correct EUV wavefront distortions.

Nanoscale multilayered structures are employed as reflective coatings for short wavelengths in a wide range of analytical and imaging technologies. Thermal stability is vital for their functionality. This thesis addresses the thermally induced internal structural changes in Mo/Si-based and La/B-based multilayers, designed for the extreme ultraviolet wavelength range. The focus of the work is to study the diffusion phenomena and the interactions between nanoscale layers, with particular emphasis on the formation of compound interlayers during thermal loading.

The physics investigations described in this thesis have been inspired by the perspective of the application of La/B-based multilayer mirrors in photolithography. This perspective however, demands the highest possible reflectance of the mirrors and full control over the multilayer growth process. The corresponding research in this thesis therefore covers the following topics: a theoretical and experimental analysis of the spectral properties of La/B-based multilayer stacks, an experimental layer composition and growth study of the candidate La/B-based multilayer optics, and the development of techniques to enable characterization of the internal structure of such multilayers.

Being of a versatile and diverse nature, the field of particle-material interaction physics has traditionally been driven by applications. Two important current drivers are materials research for thermonuclear reactors and photolithography at Extreme UV wavelength. These topics have in common that they both represent extreme conditions: high photon, particle and plasma fluxes lead to non-linear processes and complex interaction phenomena. Both focus on unravelling the material damage mechanisms involving the lightest atom, hydrogen, as the active particle. The use of a nano-scale layered material, mimicking the lithography application, afforded an opportunity to perform depth and material sensitive studies. The challenge to identify the respective processes has been undertaken in the current thesis.

Nanoscale molybdenum/silicon (Mo/Si) multilayer structures are employed as reflective optical elements for wavelengths in the extreme ultraviolet (EUV, =13.5 nm). When using appropriate ion-beam parameters, Kr+ bombardment and sputtering of a-Si layers is known to suppress layer growth intrinsic roughness in Mo/Si multilayers. In chapter 2 the scalability of the smoothing process is investigated, aiming for optimization suppression of substrate roughness. In chapter 3 is reported on modifications of the in-layer structure of a-Si layers by implantation of H+ ions. The resulting increased layer porosity is found to enhance Kr+-induced smoothing, towards ultrasmooth surfaces. In chapter 4 the interface roughness in Mo/Si multilayers as a function of the noble gas ion polishing species (Ne, Ar, Kr, and Xe) is investigated by grazing incidence small angle x-ray scattering (GISAXS). Optimal interface smoothness is obtained by Xe+ polishing, however, Kr+ polishing yields highest EUV reflectance. This is clarified by the residual amounts of polishing gas in the Si layers, affecting the optical constants. Chapter 5 discusses the application of an EUV reflective multilayer on a non-flat, grating substrate, which is appealing as a high EUV throughput optical filtering device. The deposition of multilayers onto non-flat substrate topographies as a model system for real gratings, is described in chapter 6. With these findings, multilayer deposition on a grating is shown feasible. However, the tolerances on grating roughness and flatness of the facets are extremely tight. In chapter 7 a deposition scheme of a class of rectangular grating phaseshift reflectors on flat substrates is reported.

Extreme ultraviolet lithography (EUVL) is a next generation photolithographic technique that uses 13.5 nm or Extreme UV radiation and multilayer coated reflective optics. The reflectance of these optical elements can be strongly reduced when, as a consequence of exposing the optics to EUV photons, a contamination layer is built up on the mirrors. Since this will reduce the throughput of EUV lithography machines, contamination monitoring is considered to be necessary. Direct observation of the EUV reflectance of the mirrors is hardly possible since the required accuracy can only be achieved in very sophisticated lab reflectometers. This thesis describes experimental research on the topic of EUV induced contamination and its monitoring using alternative, in situ techniques. Occasional techniques for such a task have been mentioned, but no real investigations were carried out. This thesis reviews the suggested and new techniques and describes experimental work on the three most promising: laser-generated surface acoustic waves (LG-SAWs), secondary electron yield (SEY), and spectroscopic ellipsometry (SE). The goal was not only to develop an appropriate monitoring method, but also to get insight in the material properties, both mechanical and optical, of the contamination layer in order to predict the EUV reflectance loss and the possibilities to clean the optics.

This thesis addresses the physical and chemical phenomena in Mo/Si multilayer structures with and without B4C diffusion barrier layers at the interfaces, which are applied as extreme ultraviolet (EUV) / soft X-ray optics. Since interdiffusion and interlayer formation limit both the performance and the lifetime of the optics, the interlayers and their evolution in time have been investigated in detail. To this end, a procedure was developed to utilize the depth-resolved information in a LEIS spectrum in order to non-destructively study interdiffusion in ultrathin films with sub-nanometer resolution. Using this method, it was found that the diffusion in Mo/B4C/Si layered structures initially obeys Fick’s second law. However, after a certain time, the diffusion rate instantaneously increased by up to one order of magnitude. The cause of this acceleration was found to be the amorphous-to-nanocrystalline transition of the MoSi2 interface. Besides diffusion and crystallization, the chemical processes upon annealing of Mo/B4C/Si layered structures have been identified. Mo/B/Si and Mo/C/Si samples were studied as reference systems. Initially, predominantly MoBxCy (resp. MoBx, MoCx) formed, plus small amounts of SiBxCy (resp. SiBx, SiCx). Subsequently, MoSi2 formed, while the already formed MoBxCy (resp. MoBx, MoCx) diffused further into the Mo layer. Stable silicides, through which Si diffused to form MoSi2 in the second stage, only formed in the samples with C and B4C interlayers. Furthermore, it was investigated whether the interlayer thickness can be reduced by depositing the multilayer mirror at a low temperature. Even after warming up to room temperature, the interlayers that formed upon cryogenic deposition were found to be nearly 60 % thinner than after room temperature deposition. Finally, since rough interfaces between the layers of a multilayer mirror are equivalent to thick interlayers, it is important to control the roughness during the deposition. The development of roughness is usually mitigated through ion bombardment of the Si layers. Therefore, in order to gain understanding, the roughness evolution of Si surfaces upon Ar ion erosion was studied in real-time. It was demonstrated that ion treatment can cause roughening as well as smoothening, depending on the initial roughness of the substrate.