This chapter gives an overview of the measurement capabilities of NIST and PTB and presents the status of the calibration of optics and detectors and calibration tools for EUV source metrology. EUV metrology capabilities are also provided elsewhere, e.g., at the Center for X-ray Optics (CXRO) of the Advanced Light Source (ALS) storage ring; by Paul Scherrer Institute (PSI) at the Swiss Light Source (SLS) in Switzerland; and in Japan by LASTI at the NewSUBARU storage ring.

For several decades, the National Institute of Standards and Technology (NIST) has actively supported metrology programs for extreme ultraviolet (EUV) lithography. We will describe our existing programs in optics lifetime, reflectometry, and radiometry. Recent developments include developing quantitative models for both carbonization and oxidation of optics under UV illumination and use of a cryogenic radiometer to calibrate transfer-standard detectors from 4 nm to 400 nm. We describe two programs currently in planning. The first of these is development of a method to calibrate high-power pulsed radiation detectors using a calorimeter. Our current primary standard detectors for 13 nm are based on synchrotron radiation with incident powers of a few microwatts or less. EUV production tools need to measure pulse trains with many hundreds of watts of average power. We will begin this work on our existing low-power detector-calibration facility and use higher-power beamlines with overlapping power ranges and the linearity of synchrotron radiance with stored beam current to extend the calibrations to higher powers. Second, we present a Mueller matrix ellipsometry and scatterometry system covering the far-to-extreme ultraviolet spectral range. This system is expected to achieve the requisite variable polarization and diattenuation control with an entirely reflective optical system. By extending scatterometry to short wavelengths, we intend to demonstrate improved sensitivity and accuracy of parameter retrieval from microfabricated devices. These programs complement NIST's existing far- and extreme-ultraviolet radiometry and metrology programs and expand our support for critical semiconductor manufacturing.

We demonstrate operation of a constant-pressure flowmeter capable of generating and accurately measuring flows as low as 2 × 10-13 mol/s. Generation of such small flows is accomplished by using a small conductance element with C ≈ 50 nL/s. Accurate measurement then requires both low outgassing materials (< 1 × 10-15 mol/s) and small volume changes (≈ 70 μL). We outline the present flowmeter's construction, detail its operation, and quantify its uncertainty. The type-B uncertainty is < 0.2 % (k = 1) over the entire operating range. In particular, we present an analysis of its hydraulic system, and quantify the shift and uncertainty due to the slightly compressible oil. Finally, we compare our flowmeter against a NIST standard flowmeter, and find agreement to within 0.5 % (k = 2).

After we replaced the argon mini-arc with a laser-driven light source in the Ultraviolet Spectral Comparator Facility at the National Institute of Standards and Technology (NIST), we realized that the optical power should be sufficient to use the comparator system for absolute-cryogenic radiometry. Calibrating working standard detectors directly against an absolute-cryogenic radiometer in the system used for calibrations would eliminate all uncertainties resulting from the use of transfer standards, which were calibrated in a separate system using a different light source and optics. The transfer standards are the middlemen we refer to in the title. Any uncertainty caused by differences in bandpass, out-off-band radiation, spectral purity, collimation, or data interpolation would be removed. In the end, we successfully set up a twin system resembling the Ultraviolet Spectral Comparator Facility and used this system to perform a primary calibration of several photodiodes, based on an absolute-cryogenic radiometer. Using this system, we were able to reduce relative standard uncertainties at wavelengths below 220 nm from above 1 % (k = 1) to below 0.5%. We refer to this system as the Ultraviolet Scale Realization Facility or UV-SRF.

Extreme ultraviolet (EUV) radiation can be converted to visible light using tetraphenyl butadiene (TPB) as a phosphor. 1 µm films of TPB were prepared using thermal vapor deposition of the pure material and by spin coating suspensions of TPB in high-molecular-weight polystyrene/toluene solutions. Calibrated sources and detectors were used to determine the effective photon conversion efficiency of the films for incident EUV radiation in the wavelength range of $125\;{\rm nm}\le\lambda\le 200\;{\rm nm}$125nm≤λ≤200nm. After exposure to atmosphere, the efficiency of the vapor-deposited films decreased significantly, while the efficiency of the spin-coated films remained unchanged. The production of TPB films by spin coating offers the advantages of simplicity and long-term stability.

At present, broadband radiometric LED measurements with uniform and low-uncertainty results are not available. Currently, either complicated and expensive spectral radiometric measurements or broadband photometric LED measurements are used. The broadband photometric measurements are based on the CIE standardized V(λ) function, which cannot be used in the UV range and leads to large errors when blue or red LEDs are measured in its wings, where the realization is always poor. Reference irradiance meters with spectrally constant response and high-intensity LED irradiance sources were developed here to implement the previously suggested broadband radiometric LED measurement procedure [1, 2]. Using a detector with spectrally constant response, the broadband radiometric quantities of any LEDs or LED groups can be simply measured with low uncertainty without using any source standard. The spectral flatness of filtered-Si detectors and low-noise pyroelectric radiometers are compared. Examples are given for integrated irradiance measurement of UV and blue LED sources using the here introduced reference (standard) pyroelectric irradiance meters. For validation, the broadband measured integrated irradiance of several LED-365 sources were compared with the spectrally determined integrated irradiance derived from an FEL spectral irradiance lamp-standard. Integrated responsivity transfer from the reference irradiance meter to transfer standard and field UV irradiance meters is discussed.

We present results demonstrating neutron detection via a closely spaced converter structure coupled to low pressure noble gas scintillation instrumented by a single photo-multiplier tube (PMT). The converter is dispersed throughout the gas volume using a reticulated vitreous carbon foam coated with boron carbide (B4C). A calibrated cold neutron beam is used to measure the neutron detection properties, using a thin film of enriched 10B as a reference standard. Monte Carlo computations of the ion energy deposition are discussed, including treatment of the foam random network. Results from this study indicate that the foam shadows a significant portion of the scintillation light from the PMT. The high scintillation yield of Xe appears to overcome the light loss, facilitating neutron detection and presenting interesting opportunities for neutron detector design.

Thermal neutron detection is of vital importance to many disciplines, including neutron scattering, workplace monitoring, and homeland protection. We survey recent results from our collaboration which couple low-pressure noble gas scintillation with novel approaches to neutron absorbing materials and geometries to achieve potentially advantageous detector concepts. Noble gas scintillators were used for neutron detection as early as the late 1950's. Modern use of noble gas scintillation includes liquid and solid forms of argon and xenon in the dark matter and neutron physics experiments and commercially available high pressure applications have achieved high resolution gamma ray spectroscopy. Little attention has been paid to the overlap between low pressure noble gas scintillation and thermal neutron detection, for which there are many potential benefits.

In the course of investigations of thermal neutron detection based on mixtures of $^{10}$BF$_3$ with other gases, knowledge was required of the photoabsorption cross sections of $^{10}$BF$_3$ for wavelengths between 135 and 205 nm. Large discrepancies in the values reported in existing literature led to the absolute measurements reported in this communication. The measurements were made at the SURF III synchrotron radiation facility at the National Institute of Standards and Technology. The measured absorption cross sections vary from 10$^{-20}$ cm$^2$ at 135 nm to less than 10$^{-21}$ cm$^2$ in the region from 165 to 205 nm. Three previously unreported absorption features with resolvable structure were found in the regions 135 to 145 nm, 150 to 165 nm and 190 to 205 nm. Quantum mechanical calculations, using the TD-B3LYP/aug-cc-pVDZ variant of time-dependent density functional theory implemented in Gaussian 09, suggest that the observed absorption features arise from symmetry-changing adiabatic transitions.

IR-enhanced Si photodiodes have improved radiometric and electronic characteristics as compared to other widely used Si photodiodes and can be used as responsivity standards in the wavelength range from 300 nm to 1000 nm. Their low predicted uncertainty for radiant power responsivity measurements can result in improvements in the existing monochromator-based Si responsivity scales. They have several advantages over traditionally used Si-trap detectors, such as wider acceptance angle, higher shunt resistance, and higher responsivity in the NIR region. Radiometric and electronic measurement results are discussed to illustrate these characteristics. The spectral power responsivity scales can be improved using a set of the IR-enhanced Si photodiodes not only to transfer the calibration from the cryogenic radiometer, but for use in the monochromator facility as working standards. This improvement will reduce the length of the calibration chain and create a one-step scale transfer between the cryogenic radiometer- and the monochromator-based facility.

The National Institute of Standards and Technology operates two spectral comparator facilities, both of which are used to provide detector calibrations from the ultraviolet to the near-infrared spectral range. One, the Ultraviolet Spectral Comparator Facility (UV SCF), has been in operation for more than two decades, providing one of the core calibration services. Recently, the illumination source used in the UV SCF has been changed from an argon mini-arc source to a laser-driven plasma light source. This new source has higher brightness, a smaller source size, better temporal stability, and much better conversion efficiency than the previous source. The improvements in the capabilities are summarized.

Far-ultraviolet scintillation signals have been measured in heavy noble gases (argon, krypton, xenon) following boron-neutron capture (10B(n,α)7Li) in 10B thin films. The observed scintillation yields are comparable to the yields from some liquid and solid neutron scintillators. At noble gas pressures of 107 kPa, the number of photons produced per neutron absorbed following irradiation of a 1200 nm thick 10B film was 14 000 for xenon, 11 000 for krypton, and 6000 for argon. The absolute scintillation yields from the experimental configuration were calculated using data from (1) experimental irradiations, (2) thin-film characterizations, (3) photomultiplier tube calibrations, and (4) photon collection modeling. Both the boron films and the photomultiplier tube were characterized at the National Institute of Standards and Technology. Monte Carlo modeling of the reaction cell provided estimates of the photon collection efficiency and the transport behavior of 10B(n,α)7Li reaction products escaping the thin films. Scintillation yields increased with gas pressure due to increased ionization and excitation densities of the gases from the 10B(n,α)7Li reaction products, increased frequency of three-body, excimer-forming collisions, and reduced photon emission volumes (i.e., larger solid angle) at higher pressures. Yields decreased for thicker 10B thin films due to higher average energy loss of the 10B(n,α)7Li reaction products escaping the films. The relative standard uncertainties in the measurements were determined to lie between 14% and 16%. The observed scintillation signal demonstrates that noble gas excimer scintillation is promising for use in practical neutron detectors.

A technique has been developed for coating commercial off the shelf (COTS) detector arrays with a thin, uniform layer of quantum dots. The quantum deposition is accomplished using an Optomec Aerosol Jet rapid prototyping system. When illuminated by UV andvacuumUV (VUV) the quantum dots will fluoresce and those emitted photons will be detected by the underlying detector array. The size of the quantum dots used determines the fluorescence wavelength and that would be matched to the peak sensitivity of the underlying detector array. The devices have been tested at the NIST synchrotron facility in Gaithersburg and have shown sensitivity down to 150nm. Performance at wavelengths below 150nm is limited by absorption by solvent residues from deposition process.

We describe a flow standard for gas flows in the range from 0.01 sccm to 100 sccm with a relative standard uncertainty (68% confidence) of 0.03% at 1 sccm (1 sccm 1 cm(3)/min of an ideal gas at 101325 Pa and 0 degrees C approximate to 0.74358 mu mol/s). The flow standard calibrates a secondary meter by withdrawing a piston from a cylinder held at constant pressure P while gas flows from the secondary meter into the cylinder. The flow standard can operate anywhere in the range 10 kPa < P < 300 kPa, and it can act as a flow source as well as a flow receiver. The flow standard incorporated features that improved its convenience and lowered its cost without sacrificing accuracy, specifically (1) dry sliding seals made with commercially available, easily replaced, o-rings, (2) a compact design based on a commercially available, hollow piston, and (3) a linear encoder with a small Abbe error. Published by Elsevier Ltd.

The CCPR Pilot Comparison on spectral responsivity in the 10 nm to 20 nm spectral range was carried out within the framework of the CIPM Mutual Recognition Arrangement by three laboratories: PTB (Germany), NIST (USA), and NMIJ/AIST (Japan) with PTB acting as the central and reporting laboratory. All participating laboratories used monochromatized synchrotron radiation. PTB and NIST used a cryogenic radiometer as the primary standard detector and NMIJ, an ionization chamber with extrapolation by a wavelength-independent detector. The aim of the pilot comparison was to check the accuracy of the radiometric scale of spectral responsivity in the short wavelength EUV spectral range which has recently gained in technological importance. The wavelengths of measurement were from 11.5 nm to 20 nm in 0.5 nm steps and additionally 12.2 nm. The comparison was carried out through the calibration of a group of transfer standard detectors. Two sets of three diodes of types AXUV and SXUV from International Radiation Detectors, Inc. were used for the comparison. The comparison had the form of a star comparison: Pilot–lab A–pilot–lab B–pilot, PTB acting as the pilot laboratory. All results were communicated directly to the pilot laboratory. The report describes in detail the measurements made at PTB and summarizes the reports submitted by the participants. Measurements carried out by the pilot laboratory before and after the circulation of the detectors proved that the stability of the detectors was sufficient for the comparison. For the type AXUV detectors, however, changes in their responsivity contributed to the uncertainty of the comparison. Measurement results from participants and their associated uncertainties were analyzed in this report according to the Guidelines for CCPR Comparison Report Preparation. The uncertainty contributions were separated, as to whether they are wavelength dependent or not. All bilateral DoE are well within the respective k = 2 expanded uncertainty ranges for all wavelengths. The separated non-wavelength-dependent and wavelength-dependent uncertainty contributions are consistent with the respective wavelength-averaged DoE and wavelength-dependent variations of all bilateral DoE. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCPR WG-KC

The calculability of synchrotron radiation (SR) makes electron storage rings wonderful light sources for radiometry. The broadband nature of SR allows coverage of the entire spectral region from the X-ray to the far-infrared. Compact low-energy storage rings like the Synchrotron Ultraviolet Radiation Facility SURF III are perfect sources for radiometric applications, because the output spectrum can be custom-tailored to the user's needs: low current operations can simulate the solar spectrum, changes to the electron energy can address higher-order contributions of spectrometers and monochromators, and manipulation of the source size can increase the lifetime or change the radiation density. At large multi-user facilities these special operational conditions are generally not possible, since many users have to be satisfied simultaneously. At SURF III, NIST maintains one of the best SR-based infrared to soft X-ray calibration programs in the world: standard lamp calibrations, detector calibrations, and measurements of optical properties are routinely performed at SURF with great reliability and accuracy.

We describe a null-field ellipsometric imaging system (NEIS) that provides for the real-time imaging of carbon deposition profiles on extreme-ultraviolet (EUV) optics in a vacuum system. NEIS has been demonstrated at NIST on a small chamber that is used for EUV optics lifetime testing. The system provides images of carbon deposition spots with sub-nanometer resolution thickness measurements that maintain good agreement with those from ex-situ spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). The system will be implemented on several synchrotron beamlines for real-time monitoring of carbon film growth on optics during EUV irradiation.