Grazing Incidence X-ray Reflectometry Research Articles

Effect of Annealing on Stress, Microstructure, and Interfaces of NiV/B4C Multilayers

The functionality and reliability of nanoscale multilayer devices and components are influenced by changes in stress and microstructure throughout fabrication, processing, and operation. NiV/B4C multilayers with a d-spacing of 3 nm were prepared by magnetron sputtering, and two groups of annealing experiments were performed. The stress, microstructure, and interface changes in NiV/B4C after annealing were investigated by grazing-incidence X-ray reflectometry (GIXR), grazing-incidence X-ray diffraction (GIXRD), X-ray diffuse scattering, and grazing-incidence small-angle X-ray scattering (GISAXS). The temperature dependence experiments revealed a gradual shift in the multilayer stress from compression to tension during annealing from 70 °C to 340 °C, with the stress approaching near-zero levels between 70 °C and 140 °C. The time-dependent experiments indicated that most of the stress changes occurred within the initial 10 min, which showed that prolonged annealing was unnecessary. Combining the X-ray diffraction and X-ray scattering measurements, it was found that the changes in the thickness, interface roughness, and lateral correlation length, primarily due to crystallization, drove the changes in stress and microstructure.

Narrowband Mg/SiC multilayer mirror working as high-harmonic selector at 30.4 nm wavelength

Multilayers (MLs) are a good choice for high-harmonic generation (HHG) sources for selecting single-wavelength radiation. MLs working around 30.4 nm with a significantly reduced bandwidth based on high Bragg order reflection have been designed and fabricated. The narrowband MLs were characterized using grazing incidence x-ray reflectometry, extreme ultraviolet reflectivity, and intrinsic stress measurements. The results indicate that Mg/SiC MLs designed with 3rd Bragg order have narrowest bandwidth of 0.71 nm (full width half maximum) with a spectral resolution (λ/Δλ) of 42, and reflectance of 30% under near normal incidence geometry. Based on these results, the simulation of narrowband MLs working at large incident angles demonstrates that 3rd Bragg order ML has a better spectral selectivity compared with 1st Bragg order ML for HHG sources.

The effect of energy of Ar recoil particles on the interfaces and micro-structure in Ni/Ti multilayer fabricated by direct current magnetron sputtering technique

Ni/Ti multilayers have been therefore widely used in neutron optics devices because of their excellent reflective properties for neutrons, which is strongly dependent to their interfaces and microstructure. Hence, there have been many attempts to improve the interfaces and microstructure of Ni/Ti multilayers, for example reactive sputtering, interlayers and so on. In this paper, the influence of energy of Ar recoil particles on the interface and micro-structure of Ni/Ti multilayers were completed, through varying the sputtering pressure. Firstly, the Simulation present that the decreasing of sputtering pressure would enlarge the number recoil particle proportion. Secondly, three Ni/Ti multilayers were fabricated by direct current sputtering technique with variable sputtering pressures (0.080Pa, 0.120Pa, 0.199Pa). Thirdly, the grazing incidence X-ray reflectometry (GIXRR), diffusing scattering, X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) were used to characterize the interfaces and micro-structure of these films. The measured results present that their interfacial width and roughness were variable as diseasing the sputtering pressure, and the micro-structure of Ni layers transform from (111) only to both (111) and (100). These experimental results could result from the effects of energy of both Ar recoil particles and the Ni, Ti depositing atoms.

Study of the temporal stability of the reflection coefficient in the vicinity of 58.4 nm of narrow-band Sc/Al mirrors with Si or ScNx interlayers and a MoSi2 protective cap layer

Observation of a sample of Si/Al/Sc mirror with a MoSi2 protective cap layer, which was stored in air for 40 months, showed that the peak reflectivity at a wavelength of 58.4 nm during this period decreased from 32 % to 20.5 %, and over the last 20 months of observation—from 21.5 % to 20.5 %, which indicates a significant decrease in the rate of decline and almost stabilization of the peak reflectivity at the level of 20 %. The spectral reflection peak width of this mirror at half maximum has not changed over the past 20 months and amounted to 6.3 nm. The given data of secondary ion mass spectrometry and grazing incidence X-ray reflectometry show that the decrease in reflectance of Si/Al/Sc multilayer mirrors with a MoSi2 protective cap layer is mainly due to an increase in the amount of impurities (oxygen and carbon) in the structure and on the surface of the mirrors and, to a lesser extent, due to the broadening of the interlayer boundaries. Comparison of the rate of decrease in reflectance at 58.4 nm of Sc/Al mirrors with interlayers of silicon and nitride scandium and a MoSi2 cap layer indicates that neither the material and thickness of the interlayer nor the thickness of the protective MoSi2 cap layer within 3–6 nm have a significant effect on this rate.

Influence of FeCo layer thickness on the interfacial asymmetry of FeCo/Si multilayers fabricated by direct current magnetron sputtering.

FeCo/Si is a promising material combination for polarized neutron supermirrors because of its appropriate optical constants. Five FeCo/Si multilayers with monotonically increasing FeCo layer thicknesses were fabricated. Grazing incidence x-ray reflectometry and high-resolution transmission electron microscopy were performed to characterize the interdiffusion and asymmetry of the interfaces. Selected area electron diffraction was used to determine the crystalline states of FeCo layers. It was found that the asymmetric interface diffusion layers existed in FeCo/Si multilayers. Furthermore, the FeCo layer started the transition from amorphous to crystalline when the thickness of the FeCo layer reached 4.0nm.

Structural and optical properties of narrowband Sc/Si multilayer at 46.5 nm

The Ne VII line is an intense solar line emitted from the solar transition region located at 46.5 nm with a temperature of approximately 0.5 MK. The observation of a Ne VII line is important to deepen the understanding of solar physics. For observing the Ne VII line at 46.5 nm, we have proposed a narrowband Sc/Si multilayer that could avoid the other solar emission lines going to the observatory instrument. In this article, Sc/Si multilayers with a Sc thickness ratio of 0.35 (conventional design) and 0.65 (narrowband design) were deposited. The microstructures of both multilayers were measured by grazing incidence X-ray reflectometry, X-ray diffraction, and transmission electron microscopy. The results showed that the interdiffusion at the Si-on-Sc interface was more significant than that at the Sc-on-Si interface in both multilayer. Compared with the conventional multilayer, the narrowband multilayer had a thinner Si-on-Sc interface width. The measured reflectivity of the Sc/Si multilayer with a Sc thickness ratio of 0.65 was 37.9% at 45.5 nm with a near-normal incident angle of 4.60°. The bandwidth was 3.68 nm, which is narrow enough to observe the Ne VII solar line.

Epitaxial growth and microstructure of TiN/CrOxNy periodic multilayers

The effect of epitaxial growth on the mechanical properties of periodic multilayer coatings is an important research topic. The focus of this study is the microstructure and mechanical properties of TiN/CrOxNy periodic multilayer thin films consisting of modulated TiN layers. All samples were prepared by magnetron sputtering with varying sputtering powers for the TiN layer, but the CrOxNy layer remained constant. The grazing incidence X-ray reflectometry (GIXRR) and transmission electron microscopy (TEM) results demonstrate the well-defined periodic structure of the thin films, and an accumulating distortion was observed as more layers were added along the growth direction. The results show that the TiN/CrOxNy multilayers possessed a face-centred cubic (fcc) crystal structure and exhibited a (200) preferred orientation of TiN. The thickness of the TiN layers affected the crystalline orientation of the layers. Alternate-orientation epitaxial growth of CrOxNy layers along the TiN layers occurred when N2 was introduced. The introduction of nitrogen and the thickness of the TiN template layers significantly influenced the microstructure and crystallinity of the deposited nanomultilayers. The hardness of the multilayer films was determined by the nanoindentation. The TiN/CrOxNy periodic multilayer prepared from the TiN layer by direct current (DC) sputtering power had the highest nano hardness value, 28.7Gpa.

High reflectivity Co/Mg multilayer working in the broad soft x-ray range of 350–770 eV

A Co/Mg multilayer was proposed and optimized to work in the broad soft x-ray range of 350–770 eV. The multilayers with a d-spacing of 6.0 nm showed large interface widths of 1.95–1.07 nm which were significantly improved to 0.65–0.62 nm by using a higher Co sputtering power. Grazing incidence x-ray reflectometry, atomic force microscopy, transmission electron microscopy and x-ray diffraction measurements were used to study the multilayer structure and a more ordered polycrystalline structure was found in the multilayers deposited with higher Co power, which can explain the great improvement. The effect of Ar sputtering pressure on the layer structure was also studied. The measured soft x-ray reflectivity results indicated a high reflectivity of 18%–27.5% at 400–700 eV can be reached if a saturated number of bilayers of 50 were deposited.

Internal Structure and Temporal Stability of Hard X-ray Pd/B4C Multilayer Mirrors under Different Humidity Environments

Pd/B4C multilayers with 2.5 nm of d-spacing and thick Si and B4C capping layers were fabricated to study temporal stability under storage in different environments with relative humidity of 10% and 50%. The two stored samples were investigated using grazing incidence X-ray reflectometry (GIXR), X-ray scattering (XRS), an optical microscope, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The GIXR results showed that the reflectivity of the samples under 10% humidity and 50% humidity dropped by 3% and 8%, respectively, after 13 months. The optical microscope showed that the surface of the 10% humidity sample was smooth and undamaged, whereas the surface of the 50% humidity sample significantly eroded. TEM showed that the internal multilayer structure of the sample stored in 10% humidity was well protected by the capping layers. For the sample stored in 50% humidity, a major part of the Si and B4C capping layers were wrinkled and delaminated, and some surface layers of the multilayer structure were degraded with severe diffusion of boron. The XPS results showed a relatively large amount of oxygen in the B4C capping layer of the 50% humidity sample, and an obvious oxidation of the boron was found in the B4C capping layer and the surface of the multilayer. The severe oxidation and diffusion of boron and the delamination of the capping layers caused the degradation of the Pd/B4C multilayers stored in 50% humidity.

Synthesis and structural analysis of Mo/B periodical multilayer X-ray mirrors for beyond extreme ultraviolet optics

The synthesis and structural analysis of Mo/B periodical multilayer X-ray mirrors (PMMs) for beyond extreme ultraviolet (BEUV) optics was performed. The PMMs were deposited by a combination of pulsed DC and radio frequency (RF) magnetron sputtering. The structure was analyzed by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and grazing incidence X-ray reflectometry. The formation of 0.35 nm-thick interlayers comprised of a mixture of molybdenum borides was observed at the Mo/B interfaces. Furthermore, a low interface roughness of 0.3–0.4 nm was reported. The temperature of the substrate increased due to the increase in the sputtering power. This resulted in an increase in the thickness of the interlayers and the interface roughness; subsequently, the optical properties of the PMM deteriorated. Theoretical calculations were performed based on the real structure of the PMM to predict the reflectivity at a working wavelength of 6.7 nm. The reflectivity of approximately 53% was two times higher than that of the conventional B4C-based BEUV mirrors. Based on our study results, it can be concluded that the as-synthesized PMMs will perform better than the traditional mirrors and can be effectively used for the development of the next generation of BEUV lithography.

Evolution of chemical, structural, and mechanical properties of titanium nitride thin films deposited under different nitrogen partial pressure

In this study, to explore the impact of nitrogen on chemical composition, morphology, microstructure, as well as intrinsic stress of titanium films, nitrogen-doped titanium thin films prepared by direct current reactive magnetron sputtering, with different ratio of nitrogen doping into the Argon gas, have been characterized. After the check of grazing incidence X-ray reflectometry (GIXR), thickness of all samples were ensured to be approximately 40 nm. Using the X-ray photoelectron spectroscopy (XPS) combined with X-ray diffraction (XRD), nitrogen atoms were found to transform Ti crystals from the hexagonal close-packed (hcp) α-Ti phase with Ti(100) and Ti(002) orientation to the face-centered cubic (fcc) δ-TiN phase with TiN(111) and TiN(200) orientations, accompanied by the formation of TiO and TiON. XRD diffraction patterns further revealed the expansion of the TiN lattice and the intensity transform of TiN(111) and TiN(200). Atomic force microscopy (AFM) results indicated that the surface roughness declined continuously. A compressive stress was found to increase gradually with increasing nitrogen content. Variations in stress are caused by the expansion of the crystal lattice. It is obvious that the incorporation of nitrogen into titanium films can effectively reduce the roughness, but it will result in an increase in the compressive stress. Therefore, an appropriate nitrogen partial pressure should be chosen to control the intrinsic stress while reducing the roughness effectively.

Effects of sputtering power and annealing temperature on surface roughness of gold films for high-reflectivity synchrotron radiation mirrors

Gold films deposited by direct current magnetron sputtering are used for synchrotron radiation optics. In this study, the microstructure and surface roughness of gold films were investigated for the purpose of developing high-reflectivity mirrors. The deposition process was first optimized. Films were fabricated at different sputtering powers (15, 40, 80, and 120 W) and characterized using grazing incidence X-ray reflectometry, X-ray diffraction, and atomic force microscopy. The results showed that all the films were highly textured, having a dominant Au (111) orientation, and the film deposited at 80 W had the lowest surface roughness. Subsequently, post-deposition annealing from 100 to 200 °C in a vacuum was performed on the films deposited at 80 W to investigate the effect of annealing on the microstructure and surface roughness of the films. The grain size, surface roughness, and their relationship were investigated as a function of annealing temperature. AFM and XRD results revealed that at annealing temperatures of 175 °C and below, microstructural change of the films was mainly manifested by the elimination of voids. At annealing temperatures higher than 175 °C, grain coalescence occurred in addition to the void elimination, causing the surface roughness to increase.

Soft x-ray optical constants of sputtered chromium thin films with improved accuracy in the L and M absorption edge regions

In this study, we determine with improved accuracy the complex index of refraction n = 1 − δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge.

Study of ultrathin Pt/Co/Pt trilayers modified by nanosecond XUV pulses from laser-driven plasma source

We have studied the structural mechanisms responsible for the magnetic reorientation between in-plane and out-of-plane magnetization in the (25 nm Pt)/(3 and 10 nm Co)/(3 nm Pt) trilayer systems irradiated with nanosecond XUV pulses generated with laser-driven gas-puff target plasma source of a narrow continuous spectrum peaked at wavelength of 11 nm. The thickness of individual layers, their density, chemical composition and irradiation-induced lateral strain were deduced from symmetric and asymmetric X-ray diffraction (XRD) patterns, grazing-incidence X-ray reflectometry (GIXR), grazing incidence X-ray fluorescence (GIXRF), extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) measurements. In the as grown samples we found, that the Pt buffer layers are relaxed and that the layer interfaces are sharp. As a result of a quasi-uniform irradiation of the samples, the XRD, EXAFS, GIXR and GIXRF data reveal the formation of two distinct layers composed of Pt1-xCox alloys with different Co concentrations, dependent on the thickness of the as grown magnetic Co film but with similar ∼1% lateral tensile residual strain. For smaller exposure dose (lower number of accumulated pulses) only partial interdiffusion at the interfaces takes place with the formation of a tri-layer composed of Co-Pt alloy sandwiched between thinned Pt layers, as revealed by TEM. The structural modifications are accompanied by magnetization changes, evidenced by means of magneto-optical microscopy. The difference in magnetic properties of the irradiated samples can be related to their modification in Pt1-xCox alloy composition, as the other parameters (lateral strain and alloy thickness) remain almost unchanged. The out-of-plane magnetization observed for the sample with initially 3 nm Co layer can be due to a significant reduction of demagnetization factor resulting from a lower Co concentration.

Temperature-dependent thermal properties of Ru/C multilayers.

Multilayers made of Ru/C are the most promising candidates when working in the energy region 8-20 keV. The stability of its thermal properties, including thermal expansion and thermal conduction, needs to be considered for monochromator or focusing components. Ru/C multilayers with periodic thicknesses of 3, 4 and 5 nm were investigated in situ by grazing-incidence X-ray reflectometry and diffuse scattering in order to study their thermal expansion characteristics as a function of annealing temperature up to 400°C. The thermal conductivity of multilayers with the same structure was also measured by the transient hot-wire method and compared with bulk values.

Optical properties and oxidation resistance of different transition metals for soft X-ray and EUV applications

The results of a comparative study of Ru-, Mo-, Nb- and Pd- coatings designed for grazing angle applications in the soft X-ray and extreme ultraviolet (EUV) spectrum are presented. Optical properties and temporal stability of coatings were investigated using EUV reflectometry at 13.5nm and grazing incidence X-ray reflectometry (GIXR) with Cu-Kα radiation. Nb- and Mo-coatings showed a strong inclination to surface oxidation at ambient atmosphere leading to reflectivity losses. The Pd coating as a noble transition metal showed the highest oxidation resistance over a period of one year. The best reflective properties at 13.5nm were achieved by Ru coatings. GIXR simulation results of the time dependent surface oxidation were used to predict the reflective properties of the studied coatings following four months of storage in an ambient atmosphere for a wide spectral range (5.0nm–40.0nm).

Structure and extreme ultraviolet performance of Si/C multilayers deposited under different working pressures.

Narrow bandwidth Si/C multilayer mirrors are fabricated and characterized for the Z-pinch plasma diagnostic at a wavelength of 16.5nm. To reduce the large stress of the multilayer and maintain a practical reflectivity, different working pressures, from 0.13Pa to 0.52Pa, are optimized during the deposition. The grazing incidence x-ray reflectometry (GIXR) measurement and the fitting results indicate that an interlayer was formed at the interfaces, while both the interlayer thickness and interface widths increase with larger working pressure. The surface roughness of the multilayers also increases from 0.13nm at 0.13Pa to 0.29nm at 0.52Pa, as revealed by the atomic force microscope (AFM) measurements. The multilayer stress decreases from -682MPa to -384 MPa as the working pressure increases from 0.13Pa to 0.52Pa, respectively. The experimental extreme ultraviolet (EUV) reflectivity of the samples with 20 bilayers gradually decreased from 26.3% to 18.9% with increased working pressure. The bandwidth of the reflection peak remains similar for the different samples with a full width half-maximum (FWHM) value of around 0.87nm. A maximum EUV reflectivity of 33.2% and a bandwidth of 0.64nm were achieved by the sample with 50 bilayers fabricated under a working pressure of 0.13Pa.

Thermal stability and separation characteristics of anti-sticking layers of Pt/Cr films for the hot slumping technique**Supported by CAS XTP project XDA04060605

The thermal stability and separation characteristics of anti-sticking layers of Pt/Cr films are studied in this paper. Several types of adhesion layers were investigated: 10.0 nm Pt, 1.5 nm Cr + 50.0 nm Pt, 2.5 nm Cr + 50.0 nm Pt and 3.5 nm Cr + 50.0 nm Pt fabricated using direct current magnetron sputtering. The variation of layer thickness, roughness, crystallization and surface topography of Pt/Cr films were analyzed by grazing incidence X-ray reflectometry, large angle X-ray diffraction and optical profiler before and after heating. 2.5 nm Cr + 50.0 nm Pt film exhibits the best thermal stability and separation characteristics according to the heating and hot slumping experiments. The film was also applied as an anti-sticking layer to optimize the maximum temperature of the hot slumping technique.

Interface characterization in B-based multilayer mirrors for next generation lithography

The interfaces in La/B4C and LaN/B4C multilayer mirrors designed for near normal incidence reflection of 6.x nm EUV light were investigated by grazing incidence X-ray reflectometry, high-resolution transmission electron microscopy and EUV reflectometry. The thickness and roughness asymmetries of the different interfaces in both studied systems have been identified. A development of interface roughness with an increasing number of bilayers was found by different investigation methods. For near normal incidence, R=51.1% @ λ=6.65nm could be reached with our La/B4C multilayer mirrors, whereas R=58.1% was achieved with LaN/B4C multilayers at the same wavelength.

A comparative study of structural and dielectric properties of diglycidyl ether of bisphenol A (DGEBA) cured with aromatic or aliphatic hardeners

This study aims to present structural and dielectric comparisons between two epoxy polymers. These polymers are realized by curing diglycidyl ether of bisphenol A (DGEBA) resin with either aliphatic 1,3-diaminopropane (PDA) or aromatic 4,4′-diaminodiphenyl sulfone (DDS) hardeners. They are called DGEBA/PDA and DGEBA/DDS. Several complementary techniques have been used in the present study. The structural analysis was performed using grazing incidence X-ray reflectometry. It reveals the presence of a locally ordered nanostructure in the DGEBA/DDS polymer and an amorphous character for the DGEBA/PDA one. Dielectric characterization was carried by means of dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC) and time domain spectroscopy (TDS). DRS measurements performed over wide ranges of temperature (−80 to 160 °C) and frequency (10−1–106 Hz) showed the presence of dipolar γ and α relaxations in both polymers. Nevertheless, the interfacial Maxwell–Wagner–Sillars (MWS) relaxation appeared only in DGEBA/DDS. This can be related to the local nanostructure within this polymer, which can give rise to interfaces. Relaxation parameters were deduced from the best fits of experimental data with the Havriliak–Negami model. The calculated fragility index indicates that DGEBA/DDS is more fragile than DGEBA/PDA. The loss factor e′′(f) was calculated from the isothermal discharging current measurements, using Hamon approximation. Thanks to this e′′ calculation an interfacial relaxation was revealed in the frequency range of 10−3–10−1 Hz for each investigated polymer.