This PDF file contains the front matter associated with SPIE Proceedings Volume 8501, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

This manuscript presents a review of recent advances in EUV/x-ray substrate specification, fabrication and metrology for photolithography, synchrotron sources, free-electron laser sources, solar physics and astronomy. Highlights from ultra-low- expansion glass substrates, silicon and silicon carbide substrates are presented. Selected emerging substrate materials and fabrication technologies are also discussed.

An ellipsoidal mirror is a promising type of X-ray mirror, because it can focus X-rays to nanometer size with a very large aperture and no chromatic aberration. However, ideal ellipsoidal mirrors have not yet been realized by any manufacturing method. This is partly because there is no evaluation method for its surface figure profile. In this paper, we propose and develop a method for measuring surface figure profile of ellipsoidal mirrors using phase retrieval. An optical design for soft X-ray focusing, the employed phase retrieval method and an experimental optical system specialized for wavefront measurement using a He-Ne laser are reported.

A varied-line-space grating is used in modern soft X-ray monochromators with a high resolving power. The grating parameters require high accuracy because errors of the parameters lead to the degradation of the resolving power. The parameter tolerances required to maintain a high resolving power were estimated by analytical calculation. The groove density variations of three gratings were measured with a long trace profiler. The measured errors in the parameters were found to be sufficiently small.

We report on a cross-comparison of low-spatial-frequency surface slope and height metrology with a super-polished flat X-ray mirror Si substrate fabricated for the Stanford Linear Accelerator Center Linac Coherent Light Source hard X-ray mirror system HOMS-3. The substrate with overall dimensions of 450 × 30 × 50 mm³ was specified to have a radius of curvature between 150 km and 195 km with a residual (after subtraction of the best-fit cylinder) slope variation on the level of 0.1 μrad rms, when measured in the tangential direction over a clear aperture of 380 × 5 mm². Surface slope metrology with an accuracy of better than 60 nrad rms was performed with an upgraded long trace profiler LTP-II and an auto-collimator-based developmental LTP (DLTP). The instruments are available at Advanced Light Source optical metrology laboratory. Surface figure in the height domain was characterized at the Lawrence Livermore National Laboratory X-ray science and technology group with a large field-of-view ZYGO^TM (12 in) interferometer. The error of the interferometric measurement is estimated to be approximately 0.5 nm rms. We describe in detail the experimental methods and techniques that achieved state-of-the-art metrology with the super-high quality optic under test. We also discuss the relation between surface slope and height metrology and the principle problems of their cross-comparison. We show that with some precautions cross comparison can be made reliably, providing supplemental information on urface figure quality.

The Optical Metrology Facility at the Canadian Light Source (CLS) has recently purchased MountainsMap surface analysis software from Digital Surf and we report here our experiences with this package and its usefulness as a tool for examining metrology data of synchrotron x-ray mirrors. The package has a number of operators that are useful for determining surface roughness and slope error including compliance with ISO standards (viz. ISO 4287 and ISO 25178). The software is extensible with MATLAB scripts either by loading an m-file or by a user written script. This makes it possible to apply a custom operator to measurement data sets. Using this feature we have applied the simple six-line MATLAB code for the direct least square fitting of ellipses developed by Fitzgibbon et. al. to investigate the residual slope error of elliptical mirrors upon the removal of the best-fit-ellipse. The software includes support for many instruments (e.g. Zygo, MicroMap, etc...) and can import ASCII data (e.g. LTP data). The stitching module allows the user to assemble overlapping images and we report on our experiences with this feature applied to MicroMap surface roughness data. The power spectral density function was determined for the stitched and unstitched data and compared.

Recently, a technique for optimal tuning and calibration of bendable x-ray optics using surface slope data obtained with a slope measuring long trace profiler (LTP) was developed at the Advanced Light Source (ALS) optical metrology laboratory (OML) [Opt. Eng. 48(8), 083601 (2009)]. In this technique, slope distributions measured at different settings of the bending couples at each end of a flat substrate are used to construct bender characteristic functions. Using regression analysis with the experimental characteristic functions, optimal settings of the benders that best approximate the desired shape in slope are determined. In this work, we describe a method for finding a bender’s characteristic functions based on Finite Element Analysis (FEA) of a complete mirror assembly. The accuracy of the characteristic functions found by simulation is verified by cross comparison with experimental characteristic functions for a long (450 mm) highly curved bendable mirror. The mirror has a sagittally shaped substrate developed for the ALS MERLIN beamline 4.3.0, with a total slope variation 15 mrad. Calculating FEA characteristic functions in the design stage allowed better understanding of the design of the bender’s adjustment mechanism. By calculating FEA characteristic functions a priori, we significantly decrease the time needed in the OML for tuning the mirror. Because the calculated characteristic functions are free of the errors inherent to measurements made in the lab, the tuning is even more accurate.

We demonstrate a comprehensive and broadly applicable methodology for the optimal in situ configuration of bendable soft x-ray Kirkpatrick-Baez mirrors. The mirrors used for this application are preset at the ALS Optical Metrology Laboratory prior to beamline installation. The in situ methodology consists of a new technique for simultaneously setting the height and pitch angle of each mirror. The benders of both mirrors were then optimally tuned in order to minimize ray aberrations to a level below the diffraction-limited beam waist size of 200 nm (horizontal) × 100 nm (vertical). After applying this methodology, we measured a beam waist size of 290 nm (horizontal) × 130 nm (vertical) with 1 nm light using the Foucault knife-edge test. We also discuss the utility of using a grating-based lateral shearing interferometer with quantitative wavefront feedback for further improvement of bendable optics.

We extend analytical and numerical methods recently developed at the Advanced Light Source (ALS) optical metrology laboratory (OML) for optimal tuning and calibration of bendable x-ray optics based on ex situ measurements with surface slope profilers [Opt. Eng. 48(8), 083601 (2009); Proc. SPIE 8141, 8141-19 (2011)]. We minimize the rms variation of residual slope deviations from ideal surface figure. Previously, our adjustment assumed the deviations were weighted equally across the optic. In this work, we analyze the case when the mirror length is significant with respect to the imaging conjugate. This corresponds, for example, to high de-magnification by bendable Kirkpatrick Baez mirror pairs, used near the ends of synchrotron and free electron laser beamlines for micro- and nano-focusing that often results in a very short mirror to image distance, of the same order of magnitude as the mirror’s length. In this case, contributions to focal distortion of residual errors of mirror surface figure (appearing due to mechanical alignment tolerances, sagittal shaping errors, and the limited number of adjustable parameters inherent in a two-couple bender) strongly depend on position across the optic. Specifically, the downstream deviations from exact shape should be weighted less because the rays have a shorter path to travel to the image. Here, we derive an analytical expression for the weighting function and present a mathematical background for the bending adjustment procedure for optimization of the mirror’s beamline performance. The efficacy of the optimization is demonstrated for a short-focus mirror used for diffraction limited focusing at ALS beamline 12.3.2.

A new high-speed nanoprofiler was developed in this study. This profiler measures normal vectors and their coordinates on the surface of a specimen. Each normal vector and coordinate is determined by making the incident light path and the reflected light path coincident using 5-axis controlled stages. This is ensured by output signal of quadrant photo diode (QPD). From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm based on least-squares. In this study, a concave spherical mirror with a 400 mm radius of curvature was measured. As a result, a peak of 30 nm PV was observed at the center of the mirror. Measurement repeatability was 1 nm. In addition, cross-comparison with a Fizeau interferometer was implemented and the results were consistent within 10 nm. In particular, the high spatial frequency profile was highly consistent, and any differences were considered to be caused by systematic errors.

The multi-beam long trace profiler (LTP) under development at NASA’s Marshall Space Flight Center^[1] is designed to increase the efficiency of metrology of replicated X-ray optics. The traditional LTP operates on a single laser beam that scans along the test surface to detect the slope errors. While capable of exceptional surface slope accuracy, the LTP single beam scanning has slow measuring speed. As metrology constitutes a significant fraction of the time spent in optics production, an increase in the efficiency of metrology helps in decreasing the cost of fabrication of the x-ray optics and in improving their quality. Metrology efficiency can be increased by replacing the single laser beam with multiple beams that can scan a section of the test surface at a single instance. The increase in speed with such a system would be almost proportional to the number of laser beams. A collaborative feasibility study has been made and specifications were fixed for a multi-beam long trace profiler. The progress made in the development of this metrology system is presented.

A dynamic profiler is presented that is capable of precision measurement of surface roughness in the presence of significant vibration or motion. Utilizing a special CCD camera incorporating a micro-polarizer array and a proprietary LED source, quantitative measurements were obtained with exposure times of <100 μsec. The polarization-based interferometer utilizes an adjustable input polarization state to optimize fringe contrast and signal to noise for measurement of optical surfaces ranging in reflectivity from 1 to 100%. A new phase calculation algorithm is presented that nearly eliminates phase-dependent errors resulting in shot noise limited performance. In addition to its vibration immunity, the system’s light weight, <5 kg, compact envelope, 24 x 24 x 8 cm, integrated alignment system, and multiple mounting options facilitate use both directly resting on large optical surfaces and directly mounted to polishing equipment, stands, gantries and robots. Measurement results presented show an RMS repeatability <0.005 nm and an RMS precision < 0.1nm which are achieved without active vibration isolation.

Optical components for the extreme ultraviolet (EUV) face stringent requirements for surface finish, because even small amounts of surface and interface roughness can cause significant scattering losses and impair image quality. In this paper, we investigate the roughness evolution of Mo/Si multilayers by analyzing the scattering behavior at a wavelength of 13.5 nm as well as taking atomic force microscopy (AFM) measurements before and after coating. Furthermore, a new approach to measure substrate roughness is presented, which is based on light scattering measurements at 405 nm. The high robustness and sensitivity to roughness of this method are illustrated using an EUV mask blank with a highspatial frequency roughness of as low as 0.04 nm.

High reflective multilayer mirrors are widely used as optical elements for applications such as extreme ultraviolet (EUV) microscopy, high harmonic femtosecond chemistry, solar astrophysics imaging, and synchrotron radiation. Mg-based multilayers, such as Mg/SiC, Mg/Y₂O₃ and Mg/Co are promising in the wavelength of 25-40 nm for Mg L₃ absorption edge is located at 25 nm. Mg/Co has narrower bandwidth and better thermal stability. In applications such as synchrotron radiation and solar imaging, multilayers mirrors must endure high heat loads. Thus, we investigated the thermal stability of Mg/Co multilayer and then introduced barrier layer to improve thermal stability in this paper. The interface structures evolution was studied by using X-ray reflection/scatter technique. Mg/Co multilayer can be stable when not heated above 300°C. B₄C and Zr layers were inserted into Mg/Co multilayer as interface barrier layer to improve thermal stability. According to the measured results, B₄C barrier layer is not suitable for Mg/Co multilayer, mainly due to the diffusion between Mg and B4C. The introduction of Zr can significantly improve the thermal stability of Mg/Co up to 400°C without reducing EUV reflectance. Thus, introduction of Zr barrier layer is an efficient method to improve the thermal stability of Mg/Co multilayer for EUV applications such as astronomical observation and synchrotron radiation.

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 Å. 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.

Here we report on the effort to develop a hard x-ray grating interferometry technique for application to hard x-ray optics and wavefront characterization at the Advanced Photon Source (APS), Argonne National Laboratory, USA. We will mention the motivation for developing an x-ray interferometer at the APS and discuss the design of the interferometer. We will also describe the efforts in fabricating 2-D gratings and a new type of grating having nanometer periods for high-energy x-ray applications. The preliminary results obtained using x-ray Talbot interferometers built at APS, using a broadband (pink) beam and a monochromatic beam demonstrate the importance of this tool as a metrology instrument for optics and beam wavefront diagnostics.