the coating, replication and characterization of a custom optic with peak response at 22.8 keV, using the custom-designed SANZ mandrels. Task2: carrying out modifications to the coating chamber at SAO to accommodate new, longer, custom-designed mandrels (SANZlong) that will be fabricated at NASA MSFC in FY2020. The longer mandrels are necessary to mitigate end effects observed in the replication process for the small optics currently being fabricated.

Aperiodic multilayer interference coatings are of particular interest for a variety of hard x-ray applications, including target diagnostics, astrophysics, high energy physics and free-electron lasers. Such applications require large field of view along with the highest achievable photon efficiency for their optical components, pushing reflective multilayer coatings to their limits. This work investigates the design, experimental performance, modeling and optimization of high-reflectance aperiodic multilayers. Multilayer design starts with the implementation of an analytical method developed in the literature, which calculates the most efficient coating, featuring the highest achievable reflectivity with the least number of layers. A numerical optimization step is added for smoothing of high-frequency "ripples" or to comply with any specific requirement in terms of spectral or angular response. The design process also includes material-dependent specificities (e.g. typical roughness, interlayer formation) which are often crucial for accurate prediction of actual coating performance. We applied this method to develop novel high-reflectance broadband multilayers at 17.4 keV (Mo K-alpha emission line), working at angles of grazing incidence up to 0.6 degrees. The design methods employed in this work are presented, as well as the results obtained for a few multilayer systems, including Mo/Si, W/Si and W/SiC.

This paper summarizes recent advances in the development of EUV/x-ray multilayer optics for photolithography, free- electron and tabletop lasers, and solar physics. Driven by the needs of their respective applications, the optics meet a variety of extraordinary specifications including coating thickness control in the picometer (rms) range, low coating stress, resistance to atmospheric corrosion, while at the same time maintaining high reflective performance.

In this work we have developed aperiodic Molybdenum/Silicon (Mo/Si) multilayers (MLs) to reflect 16.25 keV photons at a grazing angle of incidence of 0.6° ± 0.05°. To the best of our knowledge this is the first time this material system has been used to fabricate aperiodic MLs for hard x-rays. At these energies new hurdles arise. First of all a large number of bilayers is required to reach saturation. This poses a challenge from the manufacturing point of view, as thickness control of each ML period becomes paramount. The latter is not well defined a priori, due to the thickness of the interfacial silicide layers which has been observed to vary as a function of Mo and Si thickness. Additionally an amorphous-to-crystalline transition for Mo must be avoided in order maintain reasonably low roughness at the interfaces. This transition is well within the range of thicknesses pertinent to this study. Despite these difficulties our data demonstrates that we achieved reasonably flat ML response across the angular acceptance of ± 0.05°, with an experimentally confirmed average reflectivity of 28%. Such a ML prescription is well suited for applications in the field of hard x-ray imaging of highly diverging sources.

This paper discusses the development of (i) corrosion-resistant multilayers for the 25–80 nm region (ii) multilayer mirrors for the first 0.5-NA Micro-Exposure Tools at 13.5 nm and (iii) multilayer mirrors for the soft gamma-ray range.

X-ray diffraction provided the first means to deflect x-rays by a substantial amount. It established that the wavelength was in the 1 A range, and it became possible to deduce the structure of a crystal with atomic resolution. The success of x-ray diffraction has two important foundations. First, the small scattering amplitudes from individual atoms in a periodic structure add in phase in certain directions. The second important feature of x-ray diffraction is the reduction of radiation damage. Imaging of nonperiodic objects with diffraction-limited or atomic resolution is still a challenge for the future. This entry discusses some of the features associated with x-ray diffraction.

In last year's report [1], we discussed the design and requirements of the optical projection module (Projection Optics Box [POB]) for the 0.5-NA Micro-field Exposure Tool (MET5) and the resulting challenges. Over the course of this past year, we have completed and fully qualified the metrology of individual mirrors. All surface figure errors have been measured over seven orders of magnitude with spatial periods ranging from the full clear aperture down to 10 nm. The reproducibility of the full aperture tests measures 16 pm RMS for the M1 test and 17 pm for the M2 test with a target of 30 pm for both tests. Furthermore, we achieved excellent results on scatter and flare: For scatter, both mirrors perform about a factor of two below specification. For flare, the larger M2 mirror performs well within and the smaller M1 mirror about a factor of two below specification. In addition, we have developed processes for correcting surface figure errors for both mirrors and have successfully demonstrated high-reflectivity coatings on pathfinder mirrors. Further, we have achieved significant goals with respect to the design, assembly, metrology and alignment of the projection module. This paper reviews this progress and describes the next step in the ambitious MET5 POB development program.

In support of the Extreme Ultraviolet Lithography (EUVL) roadmap, a SEMATECH(sic)/CNSE(sic) joint program is under way to develop 13.5 nm R&D photolithography tools with small fields (micro-field exposure tools [METs]) and numerical apertures (NAs) of 0.5. The transmitted wavefront error of the two-mirror optical projection module (projection optics box [POB]) is specified to less than 1 nm root mean square (RMS) over its 30 mu m x 200 mu m image field. Not accounting for scatter and flare losses, its Strehl ratio computes to 82%. Previously reported lithography modeling on this system [1] predicted a resolution of 11 nm with a k-factor of 0.41 and a resolution of 8 nm with extreme dipole illumination. The POB's magnification (5X), track length, and mechanical interfaces match the currently installed 0.3 NA POBs [2] [3] [6], so that significant changes to the current tool platforms and other adjacent modules will not be necessary. The distance between the reticle stage and the secondary mirror had to be significantly increased to make space available for the upgraded 0.5 NA illumination modules [1].

The Solar Ultraviolet Imager (SUVI) is one of several instruments that will fly on board the next generation of Geostationary Operational Environmental Satellites (GOES) -R and -S platforms, as part of NOAA's space weather monitoring fleet. SUVI is a Generalized Cassegrain telescope that employs multilayer-coated optics that operate in six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 angstrom. Once operational, over the mission lifetime expected to last up to 10 years, SUVI will record full disk, EUV spectroheliograms every few minutes, where this data will be used to better understand the effects of solar produced EUV radiation on Earth and the near-Earth environment. The material presented herein will touch upon general aspects of the SUVI optical design, as well as the fabrication, super polishing and metrology of the fabricated mirrors, including measured EUV spectral performance.

Experimental multilayer reflectance data on flight mirrors and witnesses for three extreme ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA) instrument aboard NASA’s Solar Dynamics Observatory are presented and compared to theoretical models. The relevance of these results to the performance of the AIA instrument is discussed.

The multielement structures (zone plates and multilayer mirrors) that have been fabricated during the last two decades can be used as normal incidence imaging elements, and high-quality soft x-ray imaging has become one major application. The narrow bandwidth of the devices has also become useful for spectroscopy, often simultaneously with imaging. Applications cover many areas in science and technology such as astronomy [1, 2], microscopy [3–8], x-ray lithography [9], spectroscopy [10–12], microanalysis [13], plasma diagnostics [14–16], and soft x-ray laser research [17–19]. The earliest interference structures for x rays lost their reflectivities during aging [20, 21], and this fact has been developed into a technique to measure extremely small diffusion constants [22], and Greer [23] has reviewed this application. Data on the high-temperature stability of multilayer mirrors can be found in Refs. [24–32]. Multilayer structures are also fabricated for their electric, magnetic, mechanical, chemical, or superconducting properties. While the description of these properties is beyond the scope of this book, those structures are often characterized by the x-ray methods described in Chapter 10.

The interaction between radiation and matter is too weak in the far ultraviolet and x-ray regions to allow substantial and efficient deflection of a beam in a single step. Multiple reflections or diffraction from multielement structures are used to increase the efficiency. If the small amplitudes from all subelements are added coherently with equal phase, the efficiency can increase ∝ N2, where N is the number of subelements. However, the subelements have to be fabricated and assembled with high precision and have to be illuminated coherently. Errors in the different possible pathlengths from each part of the structure have to be small compared to the wavelength. When this requirement cannot be met, amplitudes from different parts of a structure are added with random phases. In this case the intensities from all subelements are added; i.e., the efficiency increases ∝N.

Coherence conditions define the volume of a mode and the number of modes in a radiation field. The number of spatial modes or independent channels is equal to the maximum number of pixels in a plane. The field amplitudes of thermal sources fluctuate randomly, and the superposition of different modes produces a fluctuating interference pattern (speckle) in space and time. A stationary interference pattern or a standing wave can, even for such a source, be obtained in the focal plane of a lens. The observation of interference patterns in other planes requires observation times shorter than the coherence time. Under these conditions one can observe only the photon shot noise and not the interference fringes with presently available x-ray sources. Propagation in space conserves the number of modes or the information content of a radiation field. A recording of the field on a two-dimensional surface contains sufficient information to reconstruct a two-dimensional object with high fidelity. Reconstruction of a three-dimensional scene requires a large number of two-dimensional recordings. Imaging with lenses or mirrors with incoherent illumination adds the contributions from many different coherent illuminations and allows reconstruction of each plane in a three-dimensional scene with high fidelity by a simple change of focus.

A multilayer-coated 27-cm focal length parabola, optimized to reflect 13.5 nm wavelength at normal incidence, was used in multiple FLASH experiments and focused the beam to a sub-micron beam size. The intensity of the beam was measured indirectly from the depths of craters left by the FLASH beam on PMMA-coated substrates. Comparing simulated and experimental shapes of the craters we found the best match for a wavefront error of 0.45 nm, or λ/30. We further estimated that the FWHM of the focal spot was 350 nm and that the intensity in the focus was 1018 W/cm2. The sub-micron FLASH beam provided extreme intensity conditions essential for warm dense matter experiments. The same optic was used in multiple experiments and survived the beam. However, after the first measurements, which took place over several days, the optical surface was contaminated. This contamination reduced the mirror reflectivity, which was partially recovered by oxygen plasma cleaning. However, even the partially cleaned multilayer-coated optic is still diffraction limited and can focus the beam in future experiments to a sub-micron beam size.

The authors have developed processes for producing nanoscale programed substrate defects that have applications in areas such as thin film growth, extreme ultraviolet lithography, and defect inspection. Particle, line, pit, and scratch defects on the substrates between 40 and 140nm wide, 50–90nm high have been successfully produced using e-beam lithography and plasma etching in both silicon and hydrogensilsesquioxane films. These programed defect substrates have several advantages over those produced previously using gold nanoparticles or polystyrene latex spheres—most notably, the ability to precisely locate features and produce recessed as well as bump-type features in ultrasmooth films. These programed defects were used to develop techniques for planarization of film defects and results are discussed.

Growth and Printability of Multilayer Phase Defects on EUV Mask Blanks Ted Liang, Erdem Ultanir, Guojing Zhang, Seh-Jin Park Intel Corporation, 2200 Mission College Blvd., Santa Clara, CA 94054 Erik Anderson, Eric Gullikson, Patrick Naulleau, Farhad Salmassi Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA Paul Mirkarimi, Eberhard Spiller, Sherry Baker Lawrence Livermore National Laboratory, Livermore, CA ABSTRACT The ability to fabricate defect-free mask blanks is a well-recognized challenge in enabling extreme ultraviolet lithography (EUVL) for semiconductor manufacturing. Both the specification and reduction of defects necessitate the understanding of their printability and how they are generated and grow during Mo-Si multilayer (ML) deposition. A ML phase defect can be depicted by its topographical profile on the surface as either a bump or pit, which is then characterized by height or depth and width. The complexity of such seemingly simple phase defects lies in the many ways they can be generated and the difficulties of measuring their physical shape/size and optical effects on printability. An effective way to study phase defects is to use a programmed defect mask (PDM) as ‘model’ test sample where the defects are produced with controlled growth on a ML blank and accurate placement in varying proximity to absorber patterns on the mask. This paper describes our recent study of ML phase defect printability with resist data from exposures of a ML PDM on the EUV micro-exposure tool (MET, 5X reduction with 0.3NA). 1. INTRODUCTION Projection lithography using EUV light at 13.5nm is the preferred choice for post-193nm optical patterning for high volume manufacturing of semiconductor devices 1 . One of the top three challenges for EUVL is the ability to produce quality ML blanks with zero defects 2 . Two major factors contribute to the risk in ML blank production: extremely stringent defect requirements due to the use of short wavelength of 13.5nm light and the complex and delicate steps of blank making process. For example, any defect causing a mere 3.5nm difference in the reflective EUV optical path will result in a 180 degree phase shift. While the engineering of the Mo-Si ML structure is well established and blanks can be routinely produced with good peak reflectivity and uniformity, the feasibility has yet to be demonstrated for producing of producing blanks meeting anticipated defect specifications 3 . Mask defect specifications are ultimately determined by the yield impact to device performance which correlates to resist CD (critical dimension as measured mostly by a SEM) variations in a particular lithographic patterning layer. Such methodology of gauging resist CD change is commonly referred as defect printability. However, specification for defects on ML blanks is not a trivial endeavor because of the many factors we shall consider, including not only the impact to resist imaging of patterns on the mask, but also how the device patterns will be placed on the blank during e-beam writing. For example, a ML defect located between two narrow lines may cause the lines to bridge, while the same defect may cause no harm if it were under or far away from the line. Therefore, it is not unreasonable to expect that most device layouts may tolerate the existence of a small number of defects on the ML blank. A useful ML blank may not necessarily be ‘defect-free’.

We have developed processes for producing ultra-smooth nanoscale programmed substrate defects that have applications in areas such as thin film growth, EUV lithography, and defect inspection. Particle, line, pit, and scratch defects on the substrates between 40 and 140 nm wide 50 to 90 nm high have been successfully produced using e-beam lithograpy and plasma etching in both Silicon and Hydrosilsequioxane films. These programmed defect substrates have several advantages over those produced previously using gold nanoparticles or polystyrene latex spheres--most notably, the ability to precisely locate features and produce recessed as well as bump type features in ultra-smooth films. These programmed defects were used to develop techniques for film defect mitigation and results are discussed.

The availability of defect-free mask blanks is one of the most significant challenges facing the commercialization of extreme ultraviolet lithography (EUVL). The SEMATECH Mask Blank Development Center (MBDC) was created to drive the development of EUVL mask blanks to meet the industry's needs. EUV mask defects come from two primary sources: the incoming mask substrate and defects added during multilayer deposition. For incoming defects, we have both an in-house advanced cleaning capability and an advanced in situ defect smoothing capability. This smoothing system utilizes combinations of ion beam deposition and etch to planarize any remaining incoming substrate defects. For defects added in the multilayer deposition process, we have an aggressive program to find, identify, and eliminate the defects. This paper summarizes progress in smoothing substrate defects and eliminating ever smaller multilayer-added defects. We will show the capability of our smoothing process to planarize our existing population of bump and pit type defects and discuss how quickly this can be done. We will also discuss how many defects are added by the planarization process. In addition, we will show 54 nm sensitivity defect data for multilayer-coated EUV mask blanks.

Multilayers are artificially layered structures that can be used to create optics and optical elements for a broad range of x-ray wavelengths, or can be optimized for other applications. The development of next generation x-ray sources (high brightness synchrotrons and x-ray free electron lasers) requires advances in x-ray optics. Newly developed multilayer-based mirrors and optical elements enabled efficient band-pass filtering, focusing and time resolved measurements in recent FLASH (Free Electron LASer in Hamburg) experiments. These experiments are providing invaluable feedback on the response of the multilayer structures to high intensity, short pulsed x-ray sources. This information is crucial to design optics for future x-ray free electron lasers and to benchmark computer codes that simulate damage processes.