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The Lynx x-ray mission will push thin film filters to larger apertures and thinner profiles than those of any preceding mission. We present a study of the uniformity of deposition with existing technology and the consequences of oxidation on 10-15 nm thick Al films on LUXFilm® polyimide. From visible and infrared transmission measurements of thin aluminum filters and the results of a photon-driven oxidation study at the Beamline 1 of the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology, we conclude that, from a deposition and oxidation standpoint, Al optical blocking layers at this thickness are viable.

A critical component of high-performance EUV lithography source optics is the reflecting multilayer coating. The ideal multilayer will have both high reflectance and high stability to thermal load. Additionally the capping layers must provide resistance to degradations from exposure to an EUV source, and also be compatible with, or enhance, the systems used for cleaning an exposed multilayer coating. We will report on the results of development of C and B4C stabilized Mo/Si multilayers used to increase the as-deposited peak reflectivity (Rp) as well as decreasing the loss of peak reflectivity (Rp) as a function of annealing temperature. Previous results demonstrate that these layers prevent loss of Rp for temperatures up to 600o C. Results on the use of reactively-sputtered oxide capping layers such as SiO 2 and ZrO 2 will be presented as well, along with results of exposure testing. The deposition is performed in a dual processchamber inline magnetron system, using reactive sputtering for the production of capping layers. The reflectometer and exposure apparatus at the NIST Physics Laboratory is used for evaluation of the performance. Exposure results on the resistance to oxidation in the presence of water vapor will be presented and discussed.

One of the most demanding applications of optics and optical coatings is in extreme ultraviolet lithography. Optical substrates must be polished to an accuracy of less than a nanometre, both the substrate and multilayer coatings must be atomically smooth, and the coatings must have a period that is controlled to a few tens of picometres. The metrology must have even greater capabilities to assure that the strict tolerances are met. Our extreme ultraviolet reflectometry facility has recently been furnished with the addition of a sample chamber that is capable of scanning the entire surface of a mirror up to 35 cm in diameter. The capabilities of this chamber will be described, as will the performance of the monochromator. Finally a plan will be presented to increase the stability of our monochromator in order to meet the needs of future generations of lithography tools.

We have measured the response of chromium-doped alumina screens to vacuum ultraviolet radiation and derived quantum efficiency curves for the energy range from 30 to 300 eV. A model is presented to explain the structure in this curve. In addition, the radiation hardness of such screens, which have found application as narrow-band radiation detectors for a hot fusion plasma diagnostic, is reported here for MeV electrons. Finally, a simple model is constructed to obtain the carrier diffusion length and the bulk efficiency of this material.

Laser-produced plasma (LPP) sources for extreme ultraviolet lithography (EUVL) systems utilize CO 2 lasers operating with wavelength 10.6μm. Since multilayer-coated optics have high reflectivity for this infrared radiation (IR), a significant and detrimental amount of IR is passed through the EUVL system. One method to remove the IR from the system is to utilize a binary diffraction grating. When this grating is applied directly to the surface of the primary collector optic of the source, the majority of the IR is diverted outside the radius of the exit aperture at the intermediate focus (IF). This paper will report details on the performance of a full size (410mm diameter) Demonstration Collector utilizing IR rejection (IRR) technology with the capability to produce over 125X suppression of IR, equaling the performance of a IR spectral filter. Additional details will be reported on the technology development and use of a glassy smoothing layer to enable high EUV performance, a weighted average multilayer reflectance of 50.9% for unpolarized EUV radiation.

X-ray microscopy has the capability of looking into normally opaque samples with high resolution. X rays are sensitive to elemental, structural, and chemical content and thus can provide microscopic maps of the composition and structure of a sample. X-ray microscopy has seen great growth in the last two decades in the number and types of operating instruments as well as their capabilities. This growth is due to two developments. The first is the development of high-brightness second- and third-generation synchrotron light sources that can be used with small-aperture optics. The second is a revolution in x-ray optics. In addition to the extension of commonly used visible optics, such as Fresnel zone plates and multilayer mirrors, into the x-ray regime, there has also been a dramatic improvement in grazing-incidence optics fabrication. In the range up to a few keV, Fresnel zone plates offer the highest resolution, which is below 100 nm in several instruments. Recent developments in fabrication may lead to t...

The Plasma Spectroscopy Group at the Johns Hopkins University develops high photon throughput multilayer mirror (MLM) based soft x ray and extreme ultraviolet (XUV 10 A

We report on optics contamination rates induced by exposure to broad-bandwidth, high-intensity EUV radiation peaked near 8 nm in a new beamline at the NIST synchrotron. The peak intensity of 50 mW/mm2 allows extension of previous investigations of contamination by in-band 13.5 nm radiation at intensities an order of magnitude lower. We report nonlinear pressure and intensity scaling of the contamination rates which is consistent with the earlier lower-intensity studies. The magnitude of the contamination rate per unit EUV dose, however, was found to be significantly lower for the lower wavelength exposures. We also report an apparent dose-dependent correlation between the thicknesses as measured by spectroscopic ellipsometry and XPS for the carbon deposits created using the higher doses available on the new beamline. It is proposed that this is due to different sensitivities of the metrologies to variations in the density of the deposited C induced by prolonged EUV irradiation.

Multilayers prepared with electrically isolated or grounded surfaces during deposition are shown to have dramatically different hard-x-ray, soft-x-ray, and neutron reflectivity characteristics. The effect has been observed for (100) silicon wafers, fused silica, and borate glass substrates of different sizes and with different surface roughness and flatness for multilayer structures prepared by rf and dc magnetron sputtering.

We have measured the responses of four commercial photodiodes in the vacuum ultraviolet from 20 to 600 eV and have also measured the inelastic‐electron‐scattering spectra of the materials contained in the diodes from 0 to 260 eV. Three of the diodes are silicon: an enhanced channel device, an x‐ray‐stabilized silicon diode, and a p‐i‐n diode. The fourth is a gallium arsenide phosphide Schottky diode. The diode response has been modeled by considering absorption through the surface layer and inelastic surface recombination. The model produces an excellent description of the measured responses. From our analysis we have obtained reasonable values for the number of electrons produced per eV of incident radiation, the thicknesses of the surface layers, the surface recombination velocities, and the average diffusion lengths of the minority carriers. The highest efficiency is obtained for a silicon x‐ray‐stabilized diode followed by the gallium arsenide phosphide diode. We find that both of these diodes make ex...

Extreme ultraviolet (EUV) photoresists are known to outgas during exposure to EUV radiation in the vacuum environment. This is of particular concern since some of the outgassed species may contaminate the nearby EUV optics and cause a loss of reflectivity and therefore throughput of the EUV exposure tools. Due to this issue, work has been performed to measure the species and quantities that outgas from EUV resists. Additionally, since the goal of these measurements is to determine the relative safety of various resists near EUV optics, work has been performed to measure the deposition rate of the outgassed molecules on Mo/Si-coated witness plate samples. The results for various species and tests show little measurable effect from resist components on optics contamination with modest EUV exposure doses.

Currently we are commissioning a second multilayer‐based beamline to study the radiation hardness of multilayers under extreme‐ultraviolet (EUV) irradiation in an oxidizing atmosphere. Multilayer lifetime is one of the most important issues for the commercialization of extreme‐ultraviolet lithography. The beamline employs a spherical multilayer mirror and a beryllium filter. The mirror demagnifies the source and reflects 13.4 nm radiation as well as visible light. The beryllium filter suppresses the visible light reflected by the mirror and provides also a barrier between the extremely clean storage ring vacuum and the water atmosphere of the test chamber.

The Multi-order Solar EUV Spectrograph (MOSES) is a slitless spectrograph designed to study solar He II emission at 303.8 Angstroms, to be launched on a sounding rocket payload. One difference between MOSES and other slitless spectrographs is that the images are recorded simultaneously at three spectral orders, m = -1,0, +l. Another is the addition of a narrow-band multilayer coating on both the grating and the fold flat, which will reject out-of-band lines that normally contaminate the image of a slitless instrument. The primary metrics f a the mating were high peak reflectivity and suppression of Fe XV and XVI emission lines at 284 Angstroms and 335 Angstroms, respectively. We chose B4C/Mg2Si for our material combination since it provides better values for all three metrics together than the other leading candidates Si/Ir, Si/B4C or Si/SiC. Measurements of witness flats at NIST indicate the peak reflectivity at 303.6 is 38.5% for a 15 bilayer stack, while the suppression at 284 Angstroms, is 4.5x and at 335 Angstroms is 18.3x for each of two reflections in the instrument. We present the results of coating the MOSES flight gratings and fold flat, including the spectral response of the fold flat and grating as measured at NIST's SURF III and Brookhaven's X24C beamline.

The reflectance stability of multilayer coatings for extreme ultraviolet lithography (EUVL) in a commercial tool environment is of utmost importance to ensure continuous exposures with minimum maintenance cost. We have made substantial progress in designing the protective capping layer coatings, understanding their performance and estimating their lifetimes based on accelerated electron beam and EUV exposure studies. Our current capping layer coatings have about 40 times longer lifetimes than Si-capped multilayer optics. Nevertheless, the lifetime of current Ru-capped multilayers is too short to satisfy commercial tool requirements and further improvements are essential.

Extreme ultraviolet lithography, operating at a wavelength of about 13.5 nm, will require high‐repetition‐rate pulsed sources with average power outputs of over 100 W. As the output of the sources approaches this level, the low‐power, continuous‐wave calibrations of the detectors used to determine the source output will no longer be valid. The National Institute of Standards and Technology (NIST) is currently in the process of commissioning a system for the calibration of Extreme ultraviolet detectors under pulsed conditions similar to those produced by potential sources for extreme ultraviolet lithography. This system incorporates a laser‐produced plasma source based on a Kr droplet target. The plasma’s output is collimated by a grazing incidence parabolic reflector and split by a Mo/Si multilayer beamsplitter to provide two channels of illumination. Each channel is refocused onto filtered detectors to provide two signals that are proportional to the plasma Extreme Ultraviolet (EUV) output. Calibration i...

Currently the most demanding application of extreme-ultraviolet (EUV) optics is in lithography. A commercial extreme-ultraviolet stepper will likely have six or more normal-incidence reflective optics, and the largest of these will be tens of cm in diameter. Each of the Mo/Si multilayer stepper mirrors must have the highest attainable reflectivity at 13 nm, but more importantly the central wavelength of the reflectivity must be controlled to better than 0.01 nm and the peak reflectivity of the mask reticle to better than 0.1 percent. In order to meet these demands, our group at the National Institute of Standards and Technology (NIST) has implemented several improvements to our reflectometer. Additionally, the recent upgrade of the Synchrotron Ultraviolet Radiation Facility (SURF III) allows reliable operation at a variety of stored beam energies. Utilizing this capability, and a variety of filters, we analyzed the out-of-band radiation in the system. Under optimum conditions, the out-of-band contribution of the beam incident on the sample is held to 0.4 percent, and is primarily due to correctable effects of near-band scatter. We estimate that our total uncertainty, due to both systematic effects (accuracy of our out-of-band corrections) and random effects (noise, optics heating, etc.) is better than 0.3 percent. We will also discuss improvements that have been designed and are yet to be implemented.

We describe a DC sputtering thin-film deposition chamber and load-lock system recently installed on an extreme ultraviolet beamline at the NIST Synchrotron Ultraviolet Radiation Facility (SURF II). The system allows for the measurement of reflectance vs. angle, and, from those measurements enables the determination of the optical constants of pristine films. We present preliminary results.

We have produced two new normal incidence soft x-ray telescope mirrors coated for lambda equals 63.5 angstrom wavelength: the first with a focal length f equals 1.5 m and a diameter of 25 cm for the Space Weather and Terrestrial Hazards (SWATH) satellite and the second (f equals 2 m, diameter 27.5 cm) for launch by sounding rocket (NIXT). We describe figuring and polishing of the mirror surfaces and deposition and testing of the multilayer coatings. Optimization of the mirror fabrication included grazing incidence x-ray reflectivity for quality control during polishing. In addition, the substrate and each metal layer of the Co-C multilayer coating were polished by an ion beam with in-situ roughness estimation. We explored the possibilities and limitations of telescopes for shorter wavelengths by coating several small mirrors covering the lambda equals 45 to 60 angstrom region at normal incidence and report on their performance.

A planar diode, rf-sputtering system, modified to triode operation by addition of a ring filament surrounding the anode, is described. Alternately timed sputtering is used to fabricate multilayer films with good characteristics, predominantly in the extreme ultraviolet (EUV) range of 15 to 20 nm. Fabrication of stable films of niobium/silicon is discussed, along with characterization results that utilized x-ray diffraction (XRD) and synchrotron source reflectance measurements. Characteristics of an optic that was designed and used to photograph the sun at 18.0 nm from a rocket-borne experiment are described.

In response to the needs of a solar imaging program, we designed, fabricated, and evaluated several multilayer mirror coatings for an x-ray telescope to image the sun at 9.39 nm (Fe XVIII). The telescope optic is a single-mirror Herschelian design operating at near normal incidence. Simulations using commercially available software guided preliminary multilayer mirror design. Based upon these calculations, dual ion beam assisted deposition techniques generated trial films and multilayers. Structural evaluations were carried out on a multiaxis x- ray (0.154 nm) reflectometer with specular reflection and non-specular scattering measurements. Performance parameters for the multilayers at design wavelength were obtained from the NIST EUV reflectometer at the SURF II storage ring.

Before being used in an extreme-ultraviolet (EUV) scanner, photoresists must first be evaluated for sensitivity and tested to ensure that they will not contaminate the scanner optics. The new NIST facility described here provides data on the contamination potential of the outgas products of a candidate resist by simultaneously irradiating a multilayer optic and a nearby resist-coated wafer with EUV radiation. The facility can also be used without changing its configuration to provide accurate resist dose-to-clear measurements. Detailed, real-time information on the rate of contamination growth is given by a unique, in situ imaging ellipsometer. We will describe the optical layout, mechanical design, and capabilities of the beamline, finally presenting experimental examples of its capabilities.

The lifetime of multilayer mirrors is an outstanding problem on the road to commercialization of extreme-ultraviolet (EUV) lithography. The mirrors are exposed to high-intensity EUV radiation in a vacuum with traces of water vapor and hydrocarbons. The combination of EUV and reactive species leads to chemical degradation of the mirror surfaces—carbon deposition and/or oxidation of the Si surface. In order to understand and quantify these processes, as well as to study mitigation schemes, we have constructed a dedicated synchrotron-based facility with the capability to deliver high-intensity EUV radiation in a variety of trace-gas atmospheres. The facility features a spherical Mo–Si coated mirror and a thin Be foil captured in a gate valve, which serves as both a spectral filter and vacuum seal. We will describe this facility and its performance.

Radiometric experiments often require comparatively high intensities in the extreme ultraviolet, in the microwatt range. The monochromators that provide the high throughput needed for these experiments, though, do not always allow for end stations to be switched out easily. At the National Institute of Standards and Technology Synchrotron Ultraviolet Radiation Facility, the only beamline with sufficient extreme-ultraviolet power has a multi-ton endstation, which cannot be moved. We will describe a set of transfer optics that allow the photon beam to be collimated and deflected through a port on the downstream end of the large chamber. This allowed an absolute cryogenic radiometer to be attached, with the entrance cavity underfilled. We will describe ray-tracing results and offer preliminary results of the radiometer-based throughput of the system.

We report new, near-normal-incidence, transmission grating efficiency results at selected extreme-ultraviolet wavelengths between 4.5 and 30.5 nm for two transmission gratings, one with a period of 200 nm and the other with a period of 400 nm. These gratings consist of opaque gold bars separated by open spaces that have been produced by photolithography techniques commonly used to produce electronic components. The gold bars and the open spaces are nominally of the same width. Both gratings have a thickness of 470 nm. The transmission efficiency at the central, first, and, when possible, second order of diffraction was measured. In addition, guided-wave phenomena at nonnormal angles of incidence, as well as transmission differences depending on which side of the grating was illuminated, were investigated. The observed guided-wave effects allow one to selectively enhance the transmission of the grating at desired wavelengths, as is realized with a blazed reflection grating.

Currently the most demanding application of extreme ultraviolet optics is connected with the development of extreme ultraviolet lithography. Not only does each of the Mo/Si multilayer extreme-ultraviolet stepper mirrors require the highest attainable reflectivity at 13 nm (nearly 70 %), but the central wavelength of the reflectivity of these mirrors must be measured with a wavelength repeatability of 0.001 nm and the peak reflectivity of the reflective masks with a repeatability of 0.12 %. We report on two upgrades of our NIST/DARPA Reflectometry Facility that have given us the ability to achieve 0.1 % repeatability and 0.3 % absolute uncertainty in our reflectivity measurements. A third upgrade, a monochromator with thermal and mechanical stability for improved wavelength repeatability, is currently in the design phase.

The most demanding application of extreme ultraviolet multilayer optics is in lithography. The optics in current alpha-class tools are large, and the multilayer coatings must have both optimized reflectance and extremely high uniformity. At the National Institute of Standards and Technology we have recently commissioned a very large sample chamber at the Synchrotron Ultraviolet Radiation Facility storage ring. This dedicated reflectometer is capable of carrying out complete surface maps of alpha- and beta-class tools for the extreme-ultraviolet lithography community. We have conducted a rigorous characterization of the system by varying the output spectrum of our storage ring in conjunction with multiple filter and detector combinations. This exercise has resulted in an accurate model of the effects of out-of-band radiation and scattering on the measured reflectivity. The model can be directly applied to raw data measured under any typical operating conditions to reduce the uncertainty of our measurements to 0.3%. We will report the findings of the characterization along with the resulting model and sample measurements, which show that the requisite accuracy and precision in reflectivity required for beta-class tools has been achieved. We will also present measurements of large-sized curved multilayer samples. Finally, we will report on an upgrade to the beamline’s monochromator, which is currently in progress. This will improve the stability that will yield the wavelength precision needed for all planned extreme-ultraviolet lithography tools.

We report the results of extreme-ultraviolet reflectance measurements and structural characterization of multilayer mirrors made by sequential sputter deposition of Si and B(4)C. Compared with Si/Mo multilayers, Si/B(4)C have a much narrower bandpass (deltalambda) and better off-peak rejection but lower peak reflectance (R(0)). Mirrors with three different designs gave the following results: R(0) = 0.275 and deltalambda = 0.31 nm at 13.1 nm and normal incidence; R(0) = 0.34 and deltalambda = 1.1 nm at 18.2 nm and 45 degrees ; and R(0) = 0.30 and deltalambda = 2.0 nm at 23.6 nm and 45 degrees . These multilayers exhibited excellent stability on annealing at temperatures up to 600 degrees C.