Soft X-ray Reflectivity Measurements Research Articles

Study of growth kinetics and depth resolved composition of a-SiNx:H thin films by resonant soft X-ray reflectivity at the Si L2,3-edge

Abstract Angle dependent resonant soft X-ray reflectivity (R-SoXR) measurements in the energy range (82.67–206.7 eV) were performed on PECVD grown amorphous hydrogenated silicon nitride (a-SiN x :H) thin films of different compositions near the Si– L 2,3 edge (∼100 eV). The compositional difference is reflected in the optical density ( δ ) of the two films. It is demonstrated that R-SoXR can non-destructively distinguish between the compositional variations through the depth of a given thin film, whereby it becomes possible to differentiate between the growth kinetics of the films prepared under different conditions. The compositions determined from R-SoXR, are in qualitative agreement with those determined from Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA).

Application of soft X-ray reflectometry for analysis of underlayer influence on structure of atomic-layer deposited SrTixOy films

We explored the possibility to quantify the atomic in-depth distributions by using the energy-dependent soft X-ray reflectivity (SXRR) measurements, in particular, the possibility to obtain the profiles of low-Z elements [C, N, O, Si] in heterostructures containing high concentration of higher-Z atoms [Ti, Sr, Hf]. We have shown that the SXRR technique allows one not only to quantify the atomic composition of the Sr-rich SrTixOy insulators grown on (100)Si by the Atomic Layer Deposition method but also to obtain atomic profiles across a few-nm thick underlayer (UL) inserted between SrTixOy film and the Si substrate. The accuracy of atomic concentrations and densities estimated is already sufficient to trace even small variations in composition of the SrTixOy grown by ALD on the chemically different underlayers and most it is important the composition and extension of an interfaces.

Thermal stability studies of ion beam sputter deposited C/B4C X-ray multilayer mirror

We report the results of thermal stability study carried out on C/B4C multilayer structure. We have analyzed the structure of as-deposited and vacuum annealed C/B4C multilayer film by soft X-ray reflectivity measurements. We observed that multilayer period expansion continues till 600°C and slight contraction at higher annealing temperature. The results show that the multilayer structure is stable even after 700°C annealing. Raman spectroscopy indicates graphitization of carbon layer with increasing annealing temperature. Graphitization of carbon results in increases of layer thickness and decreases in density as also observed by soft X-ray reflectivity. We observed reduction in measured soft X-ray reflectivity at 6.56 and 4.39nm wavelengths after 800°C annealing. C/B4C multilayer structure has been tested over a period of one year to investigate its temporal stability.

NbC/Si multilayer mirror for next generation EUV light sources

In the present study we report a new multilayer combination comprised of refracting layers of niobium carbide and spacer layers of silicon as a more stable and high reflecting combination for the 10 - 20 nm wavelength region. The reflectivity of the new combination is comparable to Mo/Si conventional mirrors. Annealing experiments carried out with NbC/Si multilayer at 600°C temperature showed a ~2.5% drop in the soft x-ray reflectivity along with a marginal contraction in the multilayer period length. The multilayer structure is found stable after the heat treatment. Crystallization of the niobium carbide and silicon layers is responsible for the compaction in the period length as revealed by the grazing incidence x-ray diffraction measurements. No signature of silicide formation or any other chemical species could be detected. The multilayer structures were grown by ion beam sputtering technique using a compound target of niobium carbide. Soft x-ray reflectivity measurements performed at the Indus-1 and BESSY-II synchrotron radiation sources are found in good agreement with the simulations.

Study of the optical response of Si-rich a-SiNx : H thin film near Si L2,3-edge using soft x-ray reflectivity

Angle-dependent soft x-ray reflectivity measurements in the photon energy range 82.67–248 eV near the Si L2,3 absorption edge have been performed on Si-rich a-SiNx : H (SRSN) thin film deposited by the Hg-sensitized photo-chemical vapour deposition technique. It is found that experimentally obtained δ (dispersion) values of the SRSN film lie in between that of pure silicon (Si) and silicon nitride (Si3N4). X-ray photoelectron spectroscopy measurements suggest that excess silicon is responsible for reducing optical constants values and hence by controlling the silicon amount one can tune the optical constants to desired values. We further compare the soft x-ray optical spectrum of the SRSN film with those of other silicon compounds such as silicon carbide (SiC) and silicon monoxide (SiO) near the Si L2,3 edge region to shows its possibility as a prospective material for the next generation 13.5 nm (91.85 eV) node extreme ultraviolet (EUV) lithography technology.

Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft x-ray reflectivity study

We report soft x-ray reflectivity measurements near the Si L2,3 absorption edge for Si-rich silicon nitride thin film obtained by Hg-sensitized photochemical vapor deposition. We demonstrate that the precise analysis of optical index profile derived over extended energy region gives compositional details of the film. This nondestructive approach is used in Si-rich silicon nitride film to reveal buried Si-rich interfacial layer. Further, the combined study of soft x-ray reflectivity and optical density obtained from the reflectivity fitting at various photon energies provide a qualitative estimation of the film composition and its growth.

Resonant soft X-ray reflectivity as a sensitive probe to investigate polished zinc sulphide surface

Resonant soft X-ray reflectivity measurements at and near the L 3 absorption edge of sulphur have been performed on mechanically polished zinc sulphide using Indus-1 synchrotron source. A sulphur rich surface (∼15 nm thick) consisting of two layers with gradient electron density distribution was uniquely determined. As compared to bulk ZnS, the top layer has ∼30–50% less electron density whereas, the intermediate layer has ∼10–18% less electron density. Conventional hard X-ray reflectivity measurement at Cu Kα wavelength also indicates low electron density (sulphur rich) surface of ZnS but the technique was found insensitive for unique determination of electron density distribution. Optical constants of ZnS in the soft X-ray region (100–250 eV) have been reported for the first time and were in good agreement with the theoretically reported values.

Thermal stability of Co∕SiO2 multilayers for use in the soft x-ray region

The thermal stability of Co∕SiO2 multilayers was evaluated. Multilayer samples were deposited on Si substrates by means of the ion beam sputtering method and annealed at temperatures from 100 °C to 600 °C in a vacuum furnace. For the structural and optical evaluations, small-angle x-ray diffraction measurements, soft x-ray reflectivity measurement in the 1 keV energy region, and transmission electron microscopy observations were carried out. As the results, the Co∕SiO2 multilayers annealed up to 400 °C maintained the initial multilayer structure, and kept almost the same soft x-ray reflectivity as the as-deposited sample. A deterioration of the multilayer structure caused by the growth of cobalt grains was found on the samples annealed over 500 °C, and the soft x-ray reflectivity dropped in accordance with the deterioration of the multilayer structure.

Network compaction and surface deformation in the hydrogenated silicon nitride film upon soft x-ray/VUV illumination

In the present study, modifications in a hydrogenated silicon nitride film by soft x-ray/VUV (vacuum ultra violet) radiations are investigated using in situ soft x-ray reflectivity measurements at Indus-1 synchrotron source. The illumination experiments are performed at $10\ifmmode^\circ\else\textdegree\fi{}$ grazing incidence angle at which the majority of incident radiation (belonging to $10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}\text{--}250\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) are restricted to $\ensuremath{\sim}8.0\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ depth, except near the $\mathrm{Si}\text{\ensuremath{-}}\mathrm{L}$ absorption edge $(100\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ where photons penetrate much deeper into the film and initiate photochemical changes. Resultantly, the film density has increased along with a change in surface morphology. Due to illuminations, hydrogen bonds responsible for voids and network deformation are more likely to break and pave the path for the formation of more compact ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ network. Evolution of hydrogen changes the surface morphology significantly. Atomic force microscopy confirms the formation of nano clusters at the surface. The out diffusion of hydrogen near the surface is responsible for surface deformation. Probable mechanism of surface modification and network compaction is discussed.

Ion beam sputter deposition of soft x-ray Mo∕Si multilayer mirrors

Argon ion beam sputtering is used for production of high-quality Mo∕Si multilayer Bragg mirrors with 13.4nm center peak wavelength. The growth of the layer system was monitored in situ by real-time ellipsometry at multiple wavelengths within the visible to ultraviolet spectral region. The layer thicknesses of the individual multilayer constituents are obtained by model analysis of the ellipsometry data. Quality and performance of the soft x-ray mirrors is demonstrated by transmission electron microscopy, atomic force microscopy, glancing-angle of incidence CuKα reflectivity, and near-normal incidence soft x-ray reflectivity measurements. Thickness values obtained by transmission electron microscopy, reflectometry, and ellipsometry are critically compared.

Plasma-assisted deposition of thin carbon films from methane and the influence of the plasma parameters and additional gases

Carbon films in a thickness range between 10 and 100nm were deposited on silicon and glass substrates in an RF-plasma CVD reactor using methane as precursor. Various deposition parameters were changed, such as methane gas flow, plasma power, temperature and bias voltage of the substrate, and different gases were added to the deposition process (nitrogen, hydrogen, krypton). During deposition, an in-situ soft X-ray reflectivity measurement provided information about the growing film and controlled the thickness of the film. The resulting carbon films were characterized by grazing incidence X-ray reflectometry, Auger electron spectroscopy, infrared spectroscopy and spectral ellipsometry. The results showed that the carbon films were polymeric, with a smooth surface. In addition, the photoluminescence of the films was measured. In addition, some of the films showed strong photoluminescence.

Thin molybdenum oxide films produced by molybdenum pentacarbonyl 1-methylbutylisonitrile with plasma-assisted chemical vapor deposition

Molybdenum oxide thin films were prepared by plasma-enhanced chemical vapor deposition of molybdenum pentacarbonyl 1-methylbutylisonitrile. This precursor is an interesting alternative for the commonly used molybdenum hexacarbonyl, because the substance is liquid at room temperature, offers sufficient volatility and stability to air and water. The film growth was monitored in situ by a soft X-ray reflectivity measurement. The films were deposited with different plasma gases (hydrogen and oxygen) under different conditions and analysed by Auger electron spectroscopy, X-ray diffraction and spectral ellipsometry.

Thin molybdenum oxide films produced by molybdenum pentacarbonyl 1-methylbutylisonitrile with plasma-assisted chemical vapor deposition

Molybdenum oxide thin films were prepared by plasma-enhanced chemical vapor deposition of molybdenum pentacarbonyl 1-methylbutylisonitrile. This precursor is an interesting alternative for the commonly used molybdenum hexacarbonyl, because the substance is liquid at room temperature, offers sufficient volatility and stability to air and water. The film growth was monitored in situ by a soft X-ray reflectivity measurement. The films were deposited with different plasma gases (hydrogen and oxygen) under different conditions and analysed by Auger electron spectroscopy, X-ray diffraction and spectral ellipsometry.

Metal oxide/silicon oxide multilayer with smooth interfaces produced by in situ controlled plasma-enhanced MOCVD

Molybdenum oxide/silicon oxide and tungsten oxide/silicon oxide multilayer with 24 periods and a period thickness of 9.2 nm were fabricated with plasma-enhanced MOCVD. The layer thickness was controlled by an in situ soft X-ray reflectivity measurement. For the deposition of the SiO 2 layers, a new silicon organic precursor, pentamethylcyclopentadienyldisilane (Me 5C 5Si 2H 5) was used in an O 2 remote plasma process. The high quality of multilayer interfaces was observed by cross-section transmission electron microscopy (TEM), the interface Toughness wasmeasured by hard X-ray reflectivity and diffuse scattering at grazing incidence experiments to be about 0.1 nm. Auger electron spectroscopy (AES) gives the information, that the silicon oxide is practically carbon free, and the carbon content of the metal oxides is low (<5%).

YB66– a new soft X-ray monochromator for synchrotron radiation. II. Characterization

YB66, a complex boron-rich man-made crystal, has been singled out as a potential monochromator material to disperse synchrotron soft X-rays in the 1–2 keV region. Results of a series of systematic property characterizations pertinent for this application are presented in this paper. These include Laue diffraction patterns and high-precision lattice-constant determination, etch rate, stoichiometry, thermal expansion, soft X-ray reflectivity and rocking-curve measurements, thermal load effects on monochromator performance, nature of intrinsic positive glitches and their reduction. The 004 reflection of YB66 has a reflectance of ∼3% in this spectral region. The width of the rocking curve varies from 0.25 eV at 1.1 keV to 1.0 eV at 2 keV, which is a factor of two better than that of beryl(1010) in the same energy range, and enables measurements of high-resolution XANES spectra at the Mg, Al and Si K-edges. The thermal bump on the first crystal arising from the low thermal conductivity of YB66 causes an energy drift of a few eVs with storage-ring current and necessitates periodic energy calibration with metal foils. The positive glitches in the transmission function just above the Mg K-edge have substantially been reduced using an Si or SiC mirror which suppresses the sharp reflectivity increases associated with anomalous scattering for the YB66 006 reflection at the Y L3- and L2-edges. Continual operation over the past five years of a YB66 double-crystal monochromator installed on the JUMBO beamline at Stanford Synchrotron Radiation Laboratory (SSRL) indeed proves the long-term stability of this material in synchrotron radiation under ultrahigh vacuum conditions as indicated by the invariance in rocking-curve characteristics after being exposed to an accumulative power level of ∼3 × 108 J over this period of time.Part I. Wong et al. (1990).

Thermal behaviour of Co/Si/W/Si multilayers under rapid thermal annealing

The e-beam deposited multilayers (MLS) were studied under rapid thermal annealing (RTA) between 250°C and 1000°C during 30 s. MLS with five Co/Si/W/Si periods, each 13.9 nm (MLS1) and 18 nm (MLS2) were deposited onto oxidized Si substrates. Samples were analyzed by X-ray diffraction, hard and soft X-ray reflectivity measurements and grazing incidence X-ray diffuse scattering. The MLS period, interface roughness and its lateral and vertical correlations were obtained by simulation of the hard X-ray reflectivity and diffuse scattering spectra. The MLS1 with thinner Co layers is more temperature resistant. However, its soft X-ray reflectivity is smaller. The results show that this is because of shorter lateral and vertical correlation lengths of the interface roughness which may considerably influence the X-ray reflectivity of multilayers.

W/Si multilayers deposited by hot-filament MOCVD

W/Si multilayers with eight double layers (double layer spacing d=20 nm) were deposited on Si [100] substrates using hot-filament (or hot-wire) metal organic chemical vapor deposition (MOCVD). The process was performed in a stainless steel reactor with a tungsten filament at a temperature of 1000°C and a substrate temperature of 190°C. The film thickness and growth was controlled by an in situ soft X-ray reflectivity measurement. The multilayers were characterized by cross-section transmission electron microscopy (XTEM) and sputter auger electron spectroscopy (AES). The results are compared to W/Si bilayers, which were deposited without a hot-filament at higher substrate temperatures (500–670°C).

Metal / Silicon Multilayers Produced by Low-Temperature MOCVD

AbstractW/Si and Mo/Si multilayers with 20 periods (doublelayer spacing d = 24nm) were deposited on silicon substrates using (remote-) plasma-enhanced MOCVD. The substrate temperature was below 200°C, which is necessary to avoid interdiffusion of the layers. The layer thickness and growth was controlled by an in situ soft x-ray reflectivity measurement. The characterisation of the multilayers showed an excellent growth of the silicon layers, while the metal layers are rough with embedded crystallites.

Characterization of multilayers by Fourier analysis of x-ray reflectivity

We discuss a new method to characterize multilayer structures with grazing-incidence reflectivity measurements using hard x-ray radiation, such as Cu-Kα or Mo-Kα radiation. The method is based on the analysis of the reverse Fourier transforms of the reflectivity at the Bragg peaks in q-space, the reflectivity data being obtained from an angular scan (θ−2θ). This method is faster than curve fitting of the reflectivity data, results in an accurate value of the density and thickness of both materials, and needs no pre-assumptions about the material composition and the parameters of the multilayer. The method makes a distinction between interface roughness and layer thickness errors, and is independent of measurement of the critical angle. A minor disadvantage is that only an average value of the layer thickness is determined, rather than the individual layer thicknesses. As an example our method is used to analyze small-angle reflectivity measurements of Mo/Si and Co/C multilayers. The parameters thus obtained are used to model a structure, which is subsequently used to predict the near-normal incidence reflectivity at soft x-ray wavelengths. The accuracy thus found corresponds to a relative error of 5%. The densities of a Mo/Si multilayer are determined independently with critical angle measurements to verify the values obtained from the grazing incidence reflectivity measurements. The results of the analysis of the Co/C multilayer are compared to values obtained using a conventional method based on the kinematical theory. However, the conventional method requires additional data of soft x-ray reflectivity measurements. The new method yields the same values for the multilayer parameters but does not require the extra soft x-ray measurements.

Thermal stability of [formula omitted] multilayer reflective coatings under high intensity excimer laser pulses

UHV e-beam evaporated W 1 − x Si x Si multilayers (MLs) with four different compositions ( x = 0, 0.33, 0.5 and 0.66) were XeCl laser irradiated at different fluences F ≤ 0.6 J cm −2 with number of pulses N ≤ 100. The samples were analyzed by soft X-ray reflectivity, X-ray diffraction and resistometry measurements. It was shown, that the hardness of the samples against laser irradiation increases with increasing x up to x = 0.5, then goes down again. This behavior is explained by the interplay of the suppression of the interdiffusion at the interfaces of MLs with increasing content of Si in W and the gradual decrease of the refractory nature of W when it is diluted by Si.