In a joint-development, Rohwedder and Osmic have designed and built a low-defect dual-ion beam reactive-sputtering tool. The tool has been specifically targeted for developing low-defect lithography mask photoblank coatings intended as DUV absorbers and phase-shifting films. The Osmic/Rohwedder collaboration will continue into NGL - the present tool also serves as an R&D platform for EUVL mask blanks. The deposition tool and robotic substrate handler have been integrated and delivered to Osmic in the 2nd quarter of 2003. In this paper, we present initial capability for production of thin-film lithography coatings, including spectrophotometric performance, defect levels and film uniformity. Future reports will share results from more in-depth process development and optimization.
In a joint-development, Rohwedder and Osmic have designed and built a low-defect dual-ion beam reactive-sputtering tool. The tool has been specifically targeted for developing low-defect lithography mask photoblank coatings intended as DUV absorbers and phase-shifting films. The Osmic/Rohwedder collaboration will continue into NGL -- the present tool also serves as an R&D platform for EUVL mask blanks. The deposition tool and robotic substrate handler have been integrated and delivered to Osmic in the 2nd quarter of 2003. In this paper, we present initial capability for production of thin-film lithography coatings, including spectrophotometric performance, defect levels and film uniformity. Future reports will share results from more in-depth process development and optimization.
This paper describes the beamline optics for deep-etch x-ray lithography. In order to obtain a higher reflectivity than that provided by a mirror with a monolayer coating at photon energies of 4 to 6 keV, multilayer mirrors with a constant and graded d-spacing were developed. At an energy of 6 keV, a measured reflectivity of more than 80 percent and a bandwidth of 1 keV were obtained for a mirror with a Ni/C multilayer coating and a constant d-spacing. Moreover, it was found that, for energies form 4 to 6 keV, a multilayer mirror with a graded d-spacing provided a higher reflectivity and a wider bandwidth than a mirror with a Pt monolayer coating. A multilayer reflection mirror is a promising component of beamline optics for use in microfabrication and the structural analysis of materials.
W-B4C multilayers with single d-spacing period of 2.2 nm have been deposited on 330 long by 50 mm wide Si substrates to be used as monochromators for a computed tomography application. Using magnetron sputtering and a substrate masking technique, d-spacing uniformities of +/- 0.86% and +/- 1% were obtained over a 180 mm by 100 mm area for 2.2 nm and 4.2 nm d-spacings respectively. Two separate processes were used to coat the 330 mm long substrate, wherein half of the substrate was coated in each process. A similar process was used to deposit depth graded W-B4C supermirrors on Si and CVD SiC substrates for a beamline pre-mirror application. The 330 mm long by 50 mm wide Si and 300 mm long by 79 mm wide SiC substrates were coated with 20 bi-layer supermirrors with d-spacings ranging from 4.4 nm to 10.8 nm. For an angiography research application laterally graded W-B4C multilayers were deposited on 150 mm by 120 mm silicon substrates. A strong nonlinear d-spacing gradient, from 1.6 nm to 3.8 nm was achieved across the mirror's surface in an attempt to provide uniform intensity over the reflected area. The maximum and minimum d-spacing gradient was 0.06 nm/mm and 0.003 nm/mm, respectively. We measured and mapped the d-spacing gradient using a custom Cu-Ka diffraction system. The measured d-spacings were within +/- 1.5% of the intended d-spacings.
The loss of throughput observed at higher energies for traditional grazing-incidence x-ray telescopes coated with high-Z elements can be partly countered by employing multilayers on the outermost reflectors. Using 8-keV reflectivity data from a periodic W/B4C multilayer, the expected performance of intermediate-sized telescopes of (1) the nested Kirkpatrick-Baez geometry and (2) the conical approximation to a nested Wolter-I geometry is computed. Depending on the multilayer design, the throughput was increased by a factor of 3 to 5 in a 1.5-keVwide band, or by 30% to 100% in a 3-keV-wide band. This gain is obtained at the expense of a 20% to 30% loss of throughput over the 2- to 4-keV band. These designs lend themselves well to astrophysics missions, such as spectroscopy of the H- and He-like iron emission lines (6.4 to 7.1 keV). The technology for multilayer coating, mounting, and configuring of the flat reflectors required by the Kirkpatrick-Baez telescope exists, so that an Fe-line multilayer telescope could be built today.
Multilayers as coatings for grazing incidence telescopes have the potential of effectively improving the performance of telescopes coated with high-Z elements. For broad-band high energy (+10 keV) applications the multilayers, called supermirrors, are ideal. In this presentation we present the preliminary results of a feasibility study of a multifocus Kirkpatrick-Baez telescope. We conclude that high quality multilayers can be performed on relevant thin large flat substrate with adequate uniformity, and that existing deposition chambers can produce the multilayers at a rate of 0.42 m2 per day, so that a coating reflectors for a 1200 cm2 aperture telescope would take 8.5 months. The only remaining unanswered question is whether these thin supermirror-coated reflected can be configured to a 2 - 3' tolerance.
Supermirrors are multilayer structures where the thickness of the layers down through the structure changes so that wide-band reflection occurs. The principles were developed in the mid-70s and have been used extensively for neutron optics. Absorption in the upper layers limits the attainable reflectivity for x rays. For hard x rays (>= 15 keV), the absorption, however, is low enough that it is possible to design supermirrors with 10 - 70% reflectivity in a band approximately equals 3 times the width of the total reflection regime. Supermirrors of W/Si and Ni/C have been successfully fabricated and characterized. The measured x-ray reflectivities are well accounted for by the standard dynamical theories of multilayer reflection. Hard x ray applications that could benefit from x-ray supermirror coatings include focusing and imaging instrumentation for astrophysics, collimating and focusing devices for synchrotron radiation, and particle filtering in plasma diagnostics.
Supermirrors are multilayer structures where the thickness of the layers down through the structure changes so that wide-band reflection occurs. The principles were developed in the mid-70's and have been used extensively for neutron optics. Absorption in the upper layers limits the attainable reflectivity for X-rays. For hard X-rays (>= 15 keV), the absorption, however, is low enough that it is possible to design supermirrors with 10 - 70% reflectivity in a band approximately equals 3 times the width of the total reflection regime. Supermirrors of W/Si and Ni/C have been successfully fabricated and characterized. The measured X-ray reflectivities are well accounted for by the standard dynamical theories of multilayer reflection. Hard X-ray applications that could benefit from X-ray supermirror coatings include focusing and imaging instrumentation for astrophysics, and collimating and focusing device for synchrotron radiation.
By varying the thickness of the layers in a multilayer down through the structure, it is possible to produce wide-band reflectors. We report measurements and modeling of the reflectivity of Ni/C, Mo/Si and W/Si supermirrors, at energies ranging from 8 to 130 keV, and discuss the performance of two possible applications: a Kirkpatrick-Baez telescope, and a multiwavelength hard X-ray focusing reflector. The supermirrors perform as expected, and model-fits over the full range have been attempted with some success. We conclude that the supermirror coatings do indeed look very promising as hard x-ray optics for synchrotron applications, while some work on highly nested structures and supermirror coatings on very thin large substrates is necessary, before the feasibility of employing large-area supermirrors for hard X-ray astronomy is determined.
We present a concept of continuously graded multilayer structures for medium-sized x-ray telescopes which is based on several material combinations. We show that the theoretical reflectivity characteristics of these structures make them very advantageous when applied to high energy x-ray grazing incidence telescopes. We consider the performance of continuously graded Ni/C multilayers in a multi-focus, Kirkpatrick-Baez geometry and show a significant improvement when compared to standard coatings of gold. For a total length of 3.3 m, a total aperture of 48 cm by 48 cm, and 64 foci, we obtain an effective area of 250 cm2 at 60 keV and a FWHM field of view of 6 feet. We also show that a modular array of conical telescopes (conical approximation to a Wolter-I geometry), with the same length and aperture provides similar effective areas. Energy-dispersive x-ray reflectivity data (15 - 70 keV) is presented for the first continuously graded multilayer of this kind.
High performance in normal incidence soft X-ray optical systems requires accurate control of the d-spacing across the surface of each mirror in the system. As a first step towards being able to fabricate any desired d-spacing variation, we demonstrate the ability to produce large (25 x 150 mm) flat Mo/Si multilayer coated mirrors with a d-spacing uniformity of +/- 0.4 percent. Instead of applying the approach most often taken to minimize the d-spacing variation physical shielding of the deposition source, we use a mask with a corrected profile positioned just in front of the rotating substrate to compensate for the nonuniform deposition flux. Results obtained from hard (lambda = 0.154 nm) and soft (wavelength of interest) X-ray mapping of the surface are presented along with a discussion of the technique used to control the d-spacing distribution.
Tungsten/carbon (W/C) multilayer thin films prepared by sputtering on unheated Si(100) substrates were encapsulated with various types of layer having low x-ray absorption. Isochronal annealings for 1 hr in the temperature range from 300 to 600 degree(s)C and isothermal annealings at 300 and 400 degree(s)C were carried out under ambient conditions (in air) on coated and uncoated multilayers. The encapsulated layers are: SiNx and SiO2 prepared by plasma enhanced chemical vapor deposition (PECVD) and SiC, Al2O3, C and B4C prepared by sputtering techniques. Previous studies have shown that unprotected W/C multilayers annealed in air exhibit oxidation at relatively low temperatures (approximately 300 degree(s)C). In the present study, we have used Raman scattering (RS), Auger depth profiling and scanning electron microscopy (SEM) to investigate the effects of thermal treatments on the encapsulated W/C multilayers. The results indicate that oxidation of both W and C layers takes place during annealing at temperatures which depend on the type of protective layer. For example, in the isochronal annealing experiments, multilayers coated with C, Al2O3 and B4C suffer oxidation during annealing at 400 degree(s)C, whereas multilayers coated with the other three types of protective films prevent multilayers from oxidation at annealing temperatures as high as 600 degree(s)C. SEM micrographs show that the formation of pinholes through the protective layer occurred during annealing at the temperatures for which oxidation was first detected. Auger profiling shows the loss of compositional modulation in the region reached by oxygen. A WO3 phase is identified by RS in the oxidized region, and the loss of the C layers is most likely due to the formation of carbon oxide vapors.
The need for increased neutron flux at government and university neutron scattering facilities has created a significant demand for multilayer coated surfaces with a maximum reflectivity and extension of critical angle. OSMC's progress in the development of high quality (NiC)-Ti and Fe-Si supermirrors is presented. Factors involved in the optimization of reflectivity and critical angle are discussed.
Tungsten/carbon (W/C) multilayer thin films with a nominal d spacing varying
from 2.5 to 14 nm were prepared by magnetron sputtering technique. The thicknesses of
the W and C layers were varied from 0.5 to 12 nm. The multilayers were subjected to
isochronal anneals in a quartz tube furnace in the range of 300 to 1000 C under high
purity Ar flow conditions. X-ray diffraction, Raman scattering and Auger depth
profiling were used to characterize the structure of the as-prepared and annealed
films. It is found that an overcoat layer of silicon nitride (30-50 nm) prevents the
multilayers from oxidation during the 1 hr heat treatment at temperatures as high as
1000 C in Ar flow. In all studied W/C multilayers, the carbon layers are amorphous
(up to 12 nm). The tungsten layers are also amorphous when their thicknesses are less
than 5 nm. Tungsten layers thicker than 5 nm show crystalline W peaks in addition
to the amorphous W feature. Annealing of samples with a silicon nitride protective
layer results in several structural changes which depend on annealing temperature, d
spacing, the as-deposited W layer structure and the layer thickness ratio of W to C.
For W layer thicker than C layer and W layer thickness > 4 nm and/or C layer thickness
< 1 nm, the multilayers show the initial crystal formation of microcrystalline W2C
occurring at C-W interfaces (that interface in which C was deposited on W) after 600 C
anneal, followed by a second crystallization of a-W or a-W and WC at W-C
interfaces (W was deposited on C) at the annealing temperature of 900 C. They reveal
a relatively small (< 5 %) or essentially no layer expansion. For those multilayers
having thin W layers (2 nm) and the same or thicker C layer thicknesses, the
initial crystallization takes place at both W-C and C-W interfaces at 900 C or
higher. The crystal formed is a-W or a-W and WC. The layer pair period of the
multilayers in this group increases monotonically with increasing annealing
temperature. Expansion is up to 16 % of the original d spacing and occurs in both W
and C layers at approximately equal rates. The expansion in all multilayers is
interpreted to be associated mainly with the structural ordering processes in the
amorphous W and C layers.
The x-ray characterization of multilayer coatings at very low angles on curved substrates is limited by the radius of curvature and surface dimensions. Plane and cylindrical multilayers were manufactured in the same process and characterized as deposited. After flattening the cylindrical surface and curving the plane surface, the same were recharacterized. These measurements and the techniques used to characterize cylindrical surfaces are discussed with the goal of developing techniques for future application to the characterization of spherical, elliptical, or paraboloidal surfaces.
We present a new high-precision and cost-efficient method of manufacturing aspheric crystals and pseudo-crystals. The concept including calculations, limits of precision, and manufacturing details is discussed. The advantages of this method are illustrated by the application and use of a Johansson bent quartz crystal in an x-ray sequential spectrometer. The resolving power of the spectrometer is compared with the Siemens SRS 300 and the Fisons/ARL 8420 by a comparative measurement of uranium ore. The comparison involves the detection of 0.006 Rb (K(alpha) ) present as background. Options for future investigations and applications of this method are discussed.
A high energy telescope design is presented which combines grazing incidence geometry with Bragg reflection in a graded d-spacing multilayer coating to obtain significant sensitivity up to --6O keV. The concept utilizes total reflection and first order Bragg reflection in a graded d-spacing multilayer structure in a way that higher energies are reflected from the deepest layers in the stack. The specific design presented in this paper is based on Ni/C and Mo/C structures with dspacings ranging from 25A to 100 A. X-ray reflectivity data obtained with Cu Kc1 (8. 05 keV) are presented from the first graded d-spacing structures of this kind.