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In spite of strict limits on outgassing from organic materials, some spacecraft instruments making long-term measurements of solar extreme ultraviolet (EUV) radiation still suffer significant degradation. While such measures have reduced the rate of degradation, they have not completely eliminated it in some cases. For example, in five years, the aluminum filters used in the Extreme Ultraviolet Variability Experiment (EVE) instruments onboard the Solar Dynamics Observatory (SDO) suffered losses exceeding 40% at 30.4 nm. Comparing those losses with the negligible losses of nearby zirconium filters on the same instruments indicated that the problem was not due to carbonization on the Sun-facing side of the filter. To investigate whether the loss was due to carbon deposition on the downstream face of the Al filter, we exposed the backsides of Al and Zr filters to EUV in the presence of a volatile organic solvent in the laboratory and concluded that this could not be the cause. Given that the residual gas composition in the SDO spacecraft likely has water vapor as well as organics, these findings suggest that the transmission loss in the Al filter originated with oxidation caused by UV-activated adsorbed water.

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.

Carbon contamination induced by ultraviolet (UV) radiation affects precision optics in applications as diverse as semiconductor lithography and satellite observations of the Sun. Our previous experiments have shown that low-intensity UV-induced surface contamination depends quasilogarithmically on the partial pressure of the organic contaminant due to the polydispersive nature of the surface-adsorbate system. This complex dependence presents difficulties because, without a physically motivated model, it cannot be extrapolated to low pressures. We present measurements and a model of carbon growth induced by UV exposure in the presence of tetradecane vapor. The model, which includes a coverage-dependent adsorption energy, describes the measurements over four orders of magnitude in pressure, and we expect that it can be extrapolated to the lower pressures of interest to the extreme ultraviolet lithography and solar astronomy communities. Our experience with other contaminants leads us to expect that other organic contaminants will behave similar to tetradecane. The results also provide insights into the kinetics governing coverage isotherms at extremely low partial pressures.

Interest in the use of synchrotron radiation (SR) as a source of continuum in the extreme ultraviolet (EUV) spectral region was stimulated by the 1956 Physical Review article by Diran Tomboulian and Paul Hartman [1] of Cornell University. In their all-too-brief access to the Cornell 320 MeV electron synchrotron, they showed that SR should be an extremely useful intensity standard in the EUV. They also showed the continuum nature of SR by observing structure at the K-edge of Be at 112 eV.

We investigated several types of thin-film filters for high intensity work in the extreme-ultraviolet (EUV) spectral range. In our application, with a peak EUV intensity of 2.7 W cm−2, Ni-mesh-backed Zr filters have a typical lifetime of 20 hours, at which point they suffer from pinholes and a 50 % loss of transmission. Initial trials with Si filters on Ni meshes resulted in rupture of the filters in less than an hour. A simple thermal calculation showed that the temperature rise in those filters to be about 634 K. A similar calculation indicated that using a finer mesh with thicker wires and made of Cu reduces the temperature increase to about 60 K. We have exposed a Si filter backed by such a mesh for more than 60 hours with little loss of transmission and no leaks.

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.

This paper reports on an all-out effort to reduce the intersite gap of the resist outgassing contamination growth in the results obtained under the round-robin scheme. All test sites collaborated to determine the causes of such gaps. First, it was determined that wafer temperature during exposure could impact the amount of contamination growth. We discovered a huge intersite gap of wafer temperatures among the sites by using a wafer-shaped remote thermometer with wireless transmitting capability. Second, whether the contamination-limited regime was attained during testing could have been another primary root cause for such a difference. We found that for one of the model resists whose protecting unit had lower activation energy and molecular weight the contamination-limited regime was insufficient at one test site. Third, the ratio of the exposed area to pumping speed is necessary to equalize contamination growth. We validated the effect of matching the ratio of exposure area to pumping speed on reducing the intersite gap. This study and the protocols put in place should reduce the intersite gap dramatically.

Vacuum ultraviolet (VUV) radiation, spanning the electromagnetic spectrum from about 2 nm (620 eV) to 200 nm (6.2 eV) has long been important in astronomy, solar physics, and Earth observing systems, among other applications. The National Institute of Standards and Technology (NIST) has several programs to serve the VUV user community, from the Synchrotron Ultraviolet Radiation Facility (SURF III) – a standard of irradiance from 2 to 400 nm – to measurement and calibration services for mirrors, photodiodes, and filters. We have recently reduced the uncertainty of our extreme ultraviolet (EUV) detector calibrations by implementing an absolute cryogenic radiometer on one of the SURF beamlines, and have effected several improvements to the EUV detector calibration beamline at SURF. We continue to investigate wide-bandgap semiconductors for use as solar-blind detector technologies, and have recently obtained quantum efficiency and uniformity data from 1 cm 2 active area GaN and SiC photodiodes.

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.

The NIST Extreme Ultraviolet (EUV) Reflectometry Facility was designed in the 1990s to accommodate the largest multilayer optics envisioned at that time. However, with increasing power requirements for an EUV scanner, source collection optics have grown larger and more steeply curved than the original design would allow. To accommodate these changes, the mechanical and operational parameters of the facility have been upgraded. To access the entire surface of a larger optic, an auxiliary off-axis rotation stage has been installed allowing an increase in maximum optic size from 350 mm to 450 mm. Likewise, to deal with the deeper sags and steeper slopes of these optics, we have had to significantly expand our data analysis capabilities. In order to make these measurements, the incident radiation is reflected out of the vertical plane, allowing for measurements of effectively unpolarized radiation, an advantage for EUV lithography optics such as source collectors.

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.

(2001). Extreme-ultraviolet metrology at SURF III. Synchrotron Radiation News: Vol. 14, No. 6, pp. 26-31.

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

EUV photoresists are considered as a potential source of optics contamination, since they introduce irradiation induced outgassing in the EUV vacuum environment. Therefore, before these resists can be used on e.g. ASML NXE:3100 or NXE:3300, they need to be tested in dedicated equipment according to a well-defined procedure, which is based on exposing a witness sample (WS) in the vicinity of a simultaneously exposed resist as it outgasses. Such an outgassing test infrastructure is available at many sites, but exposure modes on the witness sample and wafer can be significantly different, which potentially could lead to different test results. In this investigation, we first explored in more detail the relationship between resist outgassing as measured by RGA (Residual Gas Analysis) and the carbon growth obtained in the WS test. A good correlation was found by using a timeintegrated and mass-weighted sum of the RGA-measured mass peaks. Next, the impact of the resist exposure mode on the WS contamination result was investigated at imec, where the outgas test setup allows to expose the wafer with EUV irradiation as well as electrons in the same vacuum environment. It was found that minor differences observed in the WS test results, can be explained by adequate characterization of exposure intensity distribution and dose control. Finally the WS test results at imec from the different exposure modes were compared to the test results at NIST. The small differences in contamination that were observed could be explained by differences in test procedure, by using the time dependent RGA approach. From the combined work on outgassing measurements and WS contamination testing we have significantly improved our understanding of the relationship between outgassing and contamination processes induced by EUV photons and electrons. We have also demonstrated how to compare results obtained at different outgas testing sites, which is important in quantifying the potential risk to EUV device manufacturing posed by resist outgassing.

We report the results of structural, chemical, and extreme ultraviolet (EUV) characterization of Si/Mo multilayers grown by sputtering and by UHV evaporation. This study includes mirrors designed for normal incidence with peak reflectivities Rpeak between 22 and 24 nm, and 45° mirrors having Rpeak between 16 and 19 nm. The deposition conditions were varied to produce multilayers with a wide range of interface morphologies. A variety of techniques were used to determine the structure and composition of the multilayers, including x‐ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and Auger depth profiling. All of the mirrors have amorphous Si layers and polycrystalline Mo layers with thin amorphous alloy interlayers. We obtain good fits to the low‐angle x‐ray diffraction data only when these interlayers are taken into account. The best sputter‐deposited mirrors were made at the lowest Ar pressure studied, 3 mTorr. The best evaporated mirrors were produced at a subst...

Several generic spectrometer types have been developed for research using VUV light at synchrotron radiation sources. They all have used gratings with a constant groove spacing and they all have tried to incorporate high resolution, high throughput, rejection of second and higher order radiation, and design simplicity in their construction. The use of gratings ruled with variable spaced grooves to reduce defocus, coma, and spherical aberration was suggested almost twenty years ago. An instrument using this grating concept was built five years ago for conventional sources. The first monochromator using a variable line spaced grating was installed at the National Synchrotron Light Source almost two years ago, and a high resolution version of such an instrument has been built at the Synchrotron Radiation Center operated by the University of Wisconsin. In this presentation we review the development of monochromators using variable line space gratings and the possible applications of this type of instrumentation.

We have recently begun a series of upgrades to the NIST/ARPA National Reflectometry Facility at the Synchrotron Ultraviolet Radiation Facility. The facility currently consists of a new monochromator and the original sample manipulator which allows us to measure optical components less than 10 cm in diameter. The monochromator offers high throughput and modest resolution over the wavelength range 3.5-40 nm. In the next year we will be installing a sample manipulator that will be able to accommodate the much larger optics that will be used in future x-ray projection lithography and astronomy instruments. We offer preliminary measurements of the throughput and resolution of the new monochromator.

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.

Before being used in an extreme-ultraviolet (EUV) scanner, photoresists must be qualified to ensure that they will not excessively contaminate the scanner optics or other parts of the vacuum environment of the scanner. At the National Institute of Standards and Technology we have designed and constructed a high-throughput beamline on the Synchrotron Ultraviolet Radiation Facility (SURF III) in order to provide data on the contamination potential of the outgas products of a candidate resist by simultaneously irradiating a witness substrate and a nearby resist-coated wafer with EUV radiation, the so called witness sample test that is currently the resist qualification method required by ASML. We will present results from four sample resists that were subjected to the test. Although the witness-sample test based on irradiating the resist with EUV radiation at 13.5 nm most closely reproduces conditions in a scanner, the limited availability of suitable EUV sources to conduct such tests has led to development of an alternative method which uses e-beam irradiation in place of EUV radiation. We will also present the results of a comparison of these two methods.

The effort to develop EUVL has presented the metrologist with a set of unique challenges both in radiometry and in measuring reflectivity. Since the inception of the National Institute of Standards and Technology's (NIST's) EUV-detector-based radiometry program in 1970, there has been little need for accurate measurements of pulsed EUV sources, and the radiometric techniques in this spectral range were all tailored to continuous wave (cw) measurements. Now, however, EUV sources bright enough to be suitable for EUVL are all based on very high temperature plasmas that must be generated by extremely high power pulses. Recently some experience in pulsed radiometry has been gained through the creation of standards for pulsed radiometry connected with DUV lithography with its pulsed 248- and 193-nm laser sources. However, important differences in the spectral, temporal, and spatial characteristics of the EUV sources as contrasted with the DUV laser sources necessitate specialized approaches, still under development, that are described in Sec. 29.3. Soon after the demonstration in 1986 of the first practicable EUV mirror in the form of a Mo∕Si multilayer, NIST established a capability to measure the reflectivity of EUV mirrors for such applications as solar astronomy, plasma diagnostics, EUV laser development, and EUV microscopy. At that point, measurement accuracy of order 0.01 nm in wavelength and 2% in reflectivity seemed to provide more than adequate characterization for the applications at hand. However, the advent of EUVL made the demands much more stringent due to the imaging and illumination needs of the process. NIST has continued to perform EUV mirror calibrations since the program's inception, has increased its capabilities to meet many of the reflectometry demands of EUVL, and will continue to expand and improve the program to help meet the future needs of the industry.

The organic phosphor p-terphenyl is used as a wavelength-converter coating in some soft-x-ray detectors. We have measured the absolute photoluminescent efficiency of p-terphenyl as a function of incident photon energy from 36 to 191 eV. We have also measured changes in the efficiency caused by soft-x-ray fluence (total photons absorbed per unit area) at several photon energies in this range. We find that efficiency drops rapidly as a function of fluence, with the rate of decrease increasing with higher soft x-ray energies.

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.

The higher energy associated with extreme ultraviolet (EUV) radiation coupled with the high absorptivity of most organic polymers at these wavelengths should lead to increased excited state population and higher quantum yields of photoproducts. Polymers representative of those commonly employed in resists as well as some model polymers were selected for this study. Polymer photochemistry at EUV was catalogued as to the effect of absorbed 13.4-nm radiation on a polymer's quantum yield of chain scission (Φs) and crosslinking (Φx). In selected cases, the chain scission and crosslinking quantum yields were also compared to those previously determined at 157-, 193- and 248-nm. It was found that quantum yield values were over a magnitude greater at EUV relative to optical wavelengths.

We have measured the momentum dependent electron energy loss spectrum of solid Kr and evaluated the effective masses of the excitons for the first two principal quantum numbers of each excitonic series. We find that n = 1 excitons disperse more slowly than the n = 2 excitons of the same series indicating greater effective masses for n = 1 excitons than for n = 2 excitons within the effective mass model. For intermediate wave vectors, where the splitting of the heavy hole and light hole bands should be observable, we find no evidence for a splitting in the two bands, in conflict with band structure calculations.

Most high-temperature superconductors exhibit two-dimensional conductance; therefore the conduction electrons are localized in the third dimension, and experience the local electric field rather than the macroscopic applied field in that direction. We report model calculations which indicate that the local field leads to enhanced electron-phonon coupling in these materials which may play a role in determining the high transition temperatures.

The authors offer a historical and pedagogical introduction to the local-field problem in dielectrics. They then discuss a microscopic approach to the problem and introduce momentum dependence. Finally they apply these results to electron-phonon coupling in quasi-two-dimensional systems, in particular the high-${T}_{c}$ superconductors.

Optics in EUVL exposure tools are known to suffer reflectivity degradation, mostly from the buildup of carbon. The sources of this carbon have been difficult to identify. The vacuum cleanliness in the preproduction micro-exposure tools is monitored with a residual gas analyzer, but they have not shown carbon-containing species in sufficient concentration to account for the observed carbon buildup seen in these tools. We have developed a technique based on cryo trapping followed by gas chromatography with mass spectrometry analysis that is more sensitive to less-volatile compounds. We will present sample data on typical vacuum systems as well as a preliminary analysis of the Intel micro-exposure tool.

The primary, publicly reported cause of optic degradation in pre-production extreme-ultraviolet (EUV) lithography systems is carbon deposition. This results when volatile organics adsorb onto optic surfaces and then are cracked by EUV-induced reactions. Hence the deposition rate depends on the adsorption-desorption kinetics of the molecule-surface system as well as the basic photon-stimulated reaction rates, both of which may vary significantly for different organic species. The goal of our ongoing optics-contamination program is to estimate the contamination rate of species expected in the tool environment by exposing samples to in-band 13.5 nm light from our synchrotron in the presence of fixed partial pressures of admitted gases. Here we report preliminary results of contamination rates on TiO2-capped samples for species observed in resist-outgassing measurements (benzene, isobutene, toluene and tert-butylbenzene) in the pressure range (10-6 to 10-4) Pa which all display an unexpected logarithmic dependence on pressure. This scaling is in agreement with previous EUV exposures of other species at NIST as well as independent measurements of coverage performed at Rutgers University. These results are consistent with a molecular desorption energy that decreases with coverage due to molecular interactions (Temkin model). Use of the proper scaling law is critical when estimating optic lifetimes by extrapolating over the 3-to-6 orders of magnitude between accelerated-testing and tool-environment partial pressures.

As part of its role in providing radiometric standards in support of industry, the National Institute of Standards and Technology has been active in advancing extreme ultravio let dosimetry on various fronts. Recently, we undertook a major effort in accurately measuring the sensitivity of three extreme ultraviolet photoresists. It has been common practice to use photoresists as a transfer “standards” to dete rmine the intensity and uniformity of the radiation transmitted by extreme ultraviolet steppers. In response to preliminary results from Lawr ence Berkeley National Laboratory that showed that two “standard” photoresists were almost twice as sensitive as had been previously believed, NIST carried out similar measurements and confirmed the Berkeley resu lts. However, we have found that the assumed sensitivities are more a question of system calibration than of absolute resi st dose sensitivity. We will describe the facility we used to make these measurements. Photoresists make less than perfect radiometers. They are very non-linear, sensitive to atmosphere, and difficult to calibrate. All of these characteristics led to the disparate re sults in assumed sensitivity values. We have developed an alternate wafer-plane dosimeter based on image plates. The dosimeter is linear over several orders of magnitude, comparatively insensitive to atmosphere, and can be re-ca librated as necessary. Moreover it can pass through a stepper as any other wafer. We will describe this dosimeter in detail. Keywords: radiometry, dosimet ry, photoresists, image plates

The photoluminescent quantum efficiencies of the inorganic phosphors Y2O2S:Eu, Y2O3:Eu, La2O2S:Tm, Gd2O2S:Tb, and Sr5Cl(PO4)3:Eu have been measured in the range 17 to 450 eV. The optical properties of these phosphors from 2 to 160 eV have been determined from inelastic electron scattering measurements. Using a model which involves nonradiative recombination at the surface of the material, we relate photoluminescent efficiency to optical absorption properties, and find that surface recombination is the predominant source of efficiency loss for these materials in the soft x‐ray range. From the model, we obtain values for the diffusion length, surface recombination velocity, and bulk quantum efficiency of these materials.

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...

The photon-stimulated emission of organic molecules from the photoresist during exposure is a serious problem for extreme-ultraviolet lithography (EUVL) because the adsorption of the outgassing products on the EUV optics can lead to carbonization and subsequent reflectivity loss. In order to accurately quantify the total amount of outgassing for a given resist during an exposure, we have constructed a compact, portable chamber that is instrumented with a spinning rotor gauge and a capacitance diaphragm gauge that, unlike the more commonly used ionization gauge or quadrupole mass spectrometer, provides a direct and accurate measurement of the total pressure that is largely independent of the composition of the outgas products. We have also developed a method to perform compositional analysis on the outgas products and, more generally, on any contaminants that might be present in the stepper vacuum. The method involves collecting the vacuum contaminants in a trap cooled to liquid-nitrogen temperature. Once collected, the products from the trap are transferred to a system for analysis with gas chromatography with mass spectrometry. We will describe the workings of the instruments in detail as well as results of initial tests.

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.

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 (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.

Endurance testing of Ru-capped multilayer mirrors (MLMs) at the NIST synchrotron facility has revealed that the damage resulting from EUV irradiation in a water-dominated environment is nonlinear and may be influenced by competing oxidation and carbon-deposition processes. Concurrent results from two different environmental chambers reveal non-intuitive relationships between reflectivity loss and the admitted water-vapor partial pressure, the ambient background-gas composition, the presence or absence of hot filaments in the chamber, the EUV intensity and the irradiation dose. We discuss possible mechanisms and propose further experiments to test them. Determining the MLM lifetime from accelerated tests is a very difficult task. It is crucial that any lifetime testing procedure involves duplicate exposures for consistency, and, if possible, testing in multiple facilities.

Exposure of collector mirrors facing the hot, dense pinch plasma in plasma-based EUV light sources remains one of the highest critical issues of source component lifetime and commercial feasibility of EUV lithography technology. Studies at Argonne have focused on understanding the underlying mechanisms that hinder collector mirror performance under Sn exposure and developing methods to mitigate them. Both Sn ion irradiation and thermal evaporation exposes candidate mirrors tested (i.e., Ru, Rh and Pd) in the experimental facility known as IMPACT (Interaction of Materials with charged Particles and Components Testing). Studies have led to an understanding of how Sn energetic ions compared to Sn thermal atoms affect three main surface properties of the collector mirror: 1) surface chemical state, 2) surface structure and 3) surface morphology. All these properties are crucial in understanding how collector mirrors will respond to Sn-based EUV source operation. This is primarily due to the correlation of how variation in these properties affects the reflectivity of photons in the EUV spectral range of interest (in-band 13.5-nm). This paper discusses the first property and its impact on 13.5-nm reflectivity. Investigation in the IMPACT experiment has focused on Sn thermal and energetic particle exposure on collector mirrors (Ru, Pd and Rh) and its effect on mirror performance as a function of incident thermal flux, incident ion flux, incident angle and temperature. This is possible by a new state-of-the-art in-situ EUV reflectometry system that measures real time relative EUV reflectivity at 15-degree incidence and 13.5-nm during Sn exposure. These results are then compared to at-wavelength EUV reflectivity measurements using the newly upgraded NIST-SURF facility. Sn energetic ions at 1- keV and fluxes of about 1013 cm-2s-1 are used in conjunction with a moderate flux Sn evaporative source delivering Sn fluences ranging from 1015-1017 cm-2. The temperature of the mirror sample is locally varied between 25 and 200 C with the chemical state of the surface simultaneously monitored using X-ray photoelectron spectroscopy, and lowenergy ion scattering spectroscopy. Results demonstrate the balance between energetic and thermal Sn has on the total Sn surface fraction during exposure and its effect on the structural and reflective properties of the mirror surface.

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.

Recently, while performing extensive EUV irradiation endurance testing on Ru-capped multilayer mirrors in the presence of elevated partial pressures of water and hydrocarbons, NIST has observed that the amount of EUV-induced damage actually decreases with increasing levels of water vapor above {approx} 5 x 10{sup -7} Torr. It is thought that the admitted water vapor may interact with otherwise stable, condensed carbonaceous species in an UHV vacuum system to increase the background levels of simple gaseous carbon-containing molecules. Some support for this hypothesis was demonstrated by observing the mitigating effect of very small levels of simple hydrocarbons with the intentional introduction of methyl alcohol in addition to the water vapor. It was found that the damage rate decreased by at least an order of magnitude when the partial pressure of methyl alcohol was just one percent of the water partial pressure. These observations indicate that the hydrocarbon components of the vacuum environment under actual testing conditions must be characterized and controlled to 10{sup -11} Torr or better in order to quantify the damage caused by high levels of water vapor. The possible effects of exposure beam size and out-of-band radiation on mirror lifetime testing will also be discussed.

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.

There are many obstacles in the path to the commercialization of EUV lithography including optics lifetime and source power. The Photon Physics Group at the National Institute of Standards and Technology has programs to support the extreme-ultraviolet source and optics development community in their efforts to meet the needs of lithography tool makers. Extreme-ultraviolet detector and optics metrology have been key elements of the Photon Physics Group program for over a decade, and this program has expanded recently to allow the calibration of assembled instruments for source development metrology. This program also includes a dedicated beamline for the exposure of multilayer optics in a low-pressure water atmosphere to test the performance of optics under irradiation conditions similar to those expected in a stepper's projection optics box. In this paper we will outline our programs in multilayer optics testing and at-wavelength detector and optics metrology including descriptions of facilities, capabilities and future plans to further support the efforts to commercialize this important technology.

Silicon capped [Mo/Si] multilayer mirrors (MLM’s) can undergo oxidation by the combined effects of radiation (Extreme Ultraviolet [EUV], electron) and water vapor. This parametric study provides silicon-capped MLM oxidation rate data. The goal of this study was to determine the dependence of silicon oxidation on water vapor pressure and radiation flux density over three orders of magnitude. Previous work1 has shown that electron and 95.3 eV EUV exposures produce similar oxidation. The present study verifies that correlation and examines the effects of EUV and electron flux on the oxidation rate of the Si-capping layer. E-beam and EUV exposed areas on silicon-capped MLM samples were analyzed following radiation exposure by Auger depth profiling to determine the thickness of the oxide grown. A ruthenium (Ru) capped MLM was also exposed for 4-hours, however it showed very little oxidation under the most extreme conditions of our test matrix. Also the effect of varying the primary e-beam voltage (0.5-2.0 keV) on Si-capped MLM was examined, which showed that exposures in the 1-2 keV range produce similar results.

The absolute cryogenic radiometer (ACR), an electrical‐substitution‐based detector, is the most accurate method for measurement of radiant power in the extreme ultraviolet. At the National Institute of Standards and Technology, ACR‐based measurements are currently used as standards from the infrared and into the vacuum ultraviolet, however, no radiometric facilities are currently in operation with enough incident power to use an ACR in the extreme‐ultraviolet region. Therefore, we have installed transfer optics on an existing beamline to allow the installation of the ACR as an additional endstation. We will describe the current radiometric beamline, the ACR, and the high‐throughput beamline, and the transfer‐optical system. Finally, we will present the performance of the transfer optics and measurements of the beam profile and incident power of the new endstation.

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...

The mass absorption coefficients of tungsten and tantalum were measured with soft x-ray photons from 1450 eV to 2350 eV using an undulator source. This region includes the M3, M4, and M5 absorption edges. X-ray absorption fine structure was calculated within a real-space multiple scattering formalism; the predicted structure was observed for tungsten and to a lesser degree tantalum as well. Separately, the effects of dynamic screening were observed as shown by an atomic calculation within the relativistic time-dependent local-density approximation. Dynamic screening effects influence the spectra at the 25 % level and are observed for both tungsten and tantalum. We applied these results to characterize spatially-resolved spectra of a tungsten integrated circuit interconnect obtained using a scanning transmission x-ray microscope. The results indicate tungsten fiducial markers were deposited into silica trenches with a depths of 50 % and 60 % of the markers' heights.

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.