Charles S. Tarrio

First Solar EUV Irradiances Obtained from SOHO by the CELIAS/SEM

The first results obtained with the Solar EUV Monitor (SEM), part of the Charge, Element, and Isotope Analysis System (CELIAS) instrument, aboard the SOlar and Heliospheric Observatory (SOHO) satellite are presented. The instrument monitors the full-disk absolute value of the solar He II irradiance at 30.4 nm, and the full-disk absolute solar irradiance integrated between 0.1 nm and 77 nm. The SEM was first turned on December 15, 1995 and obtained ‘first light’ on December 16, 1995. At this time the SOHO spacecraft was close to the L-l Lagrange point, 1.5 x 106 km from the Earth towards the Sun. The data obtained by the SEM during the first four and a half months of operation will be presented. Although the period of observation is near solar minimum, the SEM data reveal strong short-term solar irradiance variations in the broad-band, central image channel, which includes solar X-ray emissions.

Design and performance of capping layers for extreme-ultraviolet multilayer mirrors

Multilayer lifetime has emerged as one of the major issues for the commercialization of extreme-ultraviolet lithography (EUVL). We describe the performance of an oxidation-resistant capping layer of Ru atop multilayers that results in a reflectivity above 69% at 13.2 nm, which is suitable for EUVL projection optics and has been tested with accelerated electron-beam and extreme-ultraviolet (EUV) light in a water-vapor environment. Based on accelerated exposure results, we calculated multilayer lifetimes for all reflective mirrors in a typical commercial EUVL tool and concluded that Ru-capped multilayers have approximately 40x longer lifetimes than Si-capped multilayers, which translates to 3 months to many years, depending on the mirror dose.

Instrumental Aspects of X-Ray Microbeams in the Range Above 1 keV

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 their application at higher energies; for now, however, sub-μm diffractive microfocusing at higher energies is usually achieved by Bragg–Fresnel optics, Fresnel optics operated in reflection using either crystal planes or multilayer coatings. Although these offer very high resolution, they have small collection apertures and limited wavelength range of operation. The Kirkpatrick–Baez mirror combination remains the most popular and versatile microprobe in the x-ray regime. These systems can operate over a very broad energy range and several facilities are now operating with micron-scale resolution. We will discuss these and some newer types of x-ray focusing schemes.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...

Optical constants of in situ-deposited films of important extreme-ultraviolet multilayer mirror materials

We have performed angle-dependent reflectance measurements of in situ magnetron sputtered films of B(4)C, C, Mo, Si, and W. The Fresnel relations were used to determine the complex index of refraction from the reflectance data in the region of approximately 35-150 eV. In the cases of Si, C, and B(4)C we found excellent agreement with published data. However, for Mo and W we found that the optical properties from 35 to 60 eV differed significantly from those in the literature.

Si/B4C narrow-bandpass mirrors for the extreme ultraviolet

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.

Tomography of integrated circuit interconnect with an electromigration void

An integrated circuit interconnect was subject to accelerated-life test conditions to induce an electromigration void. The silicon substrate was removed, leaving only the interconnect test structure encased in silica. We imaged the sample with 1750 eV photons using the 2-ID-B scanning transmission x-ray microscope at the Advanced Photon Source, a third-generation synchrotron facility. Fourteen views through the sample were obtained over a 170° range of angles (with a 40° gap) about a single rotation axis. Two sampled regions were selected for three-dimensional reconstruction: one of the ragged end of a wire depleted by the void, the other of the adjacent interlevel connection (or “via”). We applied two reconstruction techniques: the simultaneous iterative reconstruction technique and a Bayesian reconstruction technique, the generalized Gaussian Markov random field method. The stated uncertainties are total, with one standard deviation, which resolved the sample to 200±70 and 140±30 nm, respectively. The t...

Design and Performance of Capping Layers for EUV Multilayer Mirrors

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.

Smoothing of mirror substrates by thin-film deposition

Superpolished optical flats with high spatial frequency roughness below 0.1 nm have been commercially available for years. However, it is much more difficult to obtain figured optics of similar quality. We have obtained and tested the finish of figured optics from different vendors by atomic force microscopy and optical profilometry and have investigated how the substrate quality can be improved by the deposition of thin films. We have determined the growth parameters of several thin-film structures. From these parameters we can determine how the surface topography of a coated mirror differs from that of the substrate, select the best thin-film structure, and predict the possible improvement.

Synchrotron beamline for extreme-ultraviolet multilayer mirror endurance testing

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.

Accelerated lifetime metrology of EUV multilayer mirrors in hydrocarbon environments

The ability to predict the rate of reflectivity loss of capped multilayer mirrors (MLMs) under various conditions of ambient vacuum composition, intensity, and previous dose is crucial to solving the mirror lifetime problem in an EUV stepper. Previous measurements at NIST have shown that reflectivity loss of MLMs exposed under accelerated conditions of dose and pressure can be a very complicated function of these variables. The present work continues this effort and demonstrates that reflectivity loss does not scale linearly for accelerated exposure doses over the range of 0-350 J/mm2 either for partial pressures of MMA in the range 10-8-10-7 Torr or acetone in the range 10-7-10-6 Torr. We suggest that this nonlinear scaling may be the result of a varying damage rate as the surface of the growing contamination layer moves through the EUV standing wave created by exposure of any MLM to resonant radiation. To further investigate the potential influence of these resonance effects, we report new measurements showing large variations of the secondary electron yield as a function of thickness of carbon deposited on top of a MLM.