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We investigated the thermal stability of e-beam deposited Mo/B4C/Si/B4C layered systems, with and without ion assistance during the growth of the B4C diffusion barrier layers. The thermal stability was investigated by in situ thermal annealing during grazing incidence X-ray reflection. By studying partially treated B4C barrier layers, we found that the improvement in thermal stability is caused by an enhanced density of the B4C layer. [ABSTRACT FROM AUTHOR]

We developed and demonstrate an analysis method in which we calibrate the intensity scale of cross-sectional transmission electron microscopy (TEM) using Cu Kα reflectometry. This results in quantitative in-depth density profiles of multilayer structures. Only three free parameters are needed to obtain the calibrated profiles, corresponding to three TEM image intensity levels. Additionally, the optical indices of the two multilayer materials used and the assumption that the layers are laterally homogeneous are used in the model. The power and the general usefulness of the method is demonstrated using experimental data of W/Si and Mo/Si multilayer systems with sharp interfaces as well as multilayers of which the interfaces were deliberately intermixed. [ABSTRACT FROM AUTHOR]

Presents a study to optimize the growth process of Mo/Si multilayers, while observing the effect of an elevated susbstrate temperature during deposition in a temperature range of 300 K and 550 K. Details on methodology used to conduct study; Results of study; Discussion on findings.

Investigates the process of ion bombardment for the fabrication of Mo/Si multilayer x-ray mirrors using e-beam evaporation. Application of the ion treatment after deposition of each of the Si layers; Analysis of multilayer structures; Determination of interface roughness.

Highlights: [•] In vacuum study of nanometers thick molybdenum silicon layers and multilayers under growth conditions used for typical Mo/Si multilayer optics. [•] Scanning tunneling microscopy of these layers allows detailed morphology characterization up to lateral dimensions of 1nm at any time during multilayer growth. [•] Both silicon and molybdenum layers contribute to an equal amount to the surface morphology of Mo/Si multilayers. [ABSTRACT FROM AUTHOR]

Abstract: Thin interlayers are essential for high-quality multilayer optics. We present the first investigation of reducing the interlayer thickness of Mo/Si multilayer structures by cooling the substrate with liquid nitrogen during the deposition. The structures were deposited by means of electron beam evaporation. Even after warming up to room temperature prior to analysis, the interlayers that formed upon cryogenic deposition were found to be approximately 60% thinner compared to room temperature deposition. The interlayer thickness reduction at low temperature and its preservation upon warming up are attributed to a lower mobility of adatoms, reduced surface segregation of Si during Mo-on-Si growth, and/or crystallization of Mo. [Copyright &y& Elsevier]

Abstract: We present a low temperature diffusion study on the formation of intermixing zones between periodic, nanometer thick films consisting of Mo and Si. An in-situ X-ray diffraction method at pm-accuracy was developed, including a model that explains the period change observed by diffusion limited interface growth. Experiments were carried out on Mo/Si multilayered films in the temperature range of 100–275°C, resulting in the determination of diffusion coefficients. Temperature scaling showed Arrhenius-type behavior of the diffusion constant over the entire temperature range, with an activation energy of 0.5eV. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the influence of the Mo crystalline state (quasi-amorphous or crystalline) on the thermal stability of Mo/Si thin film multilayers with B4C diffusion barrier layers at either of the two interfaces. We find that multilayers containing amorphous Mo layers are more stable than those containing crystalline layers. This observation is in contrast to the case where Si3N4 diffusion barriers are used. Using X-ray diffraction, X-ray reflection and X-ray photo-electron spectroscopy we show that this difference can be attributed to the dissociation of B4C followed by diffusion of B in Mo. Due to the favorable thermodynamic properties of MoxBy compounds, the boron atoms react with the Mo layer, forming a MoxBy layer that effectively improves the multilayer thermal resistance. [ABSTRACT FROM AUTHOR]

Abstract: Si/SiC multilayer systems for XUV reflection optics with a periodicity of 10–20nm were produced by sequential deposition of Si and implantation of 1keV ions. Only about 3% of the implanted carbon was transferred into the SiC, with a thin, 0.5–1nm, buried SiC layer being formed. We investigated the effect of thermal annealing on further completion of the carbide layer. For the annealing we used a vacuum furnace, a rapid thermal annealing system in argon atmosphere, and a scanning e-beam, for different temperatures, heating rates, and annealing durations. Annealing to a temperature as low as 600°C resulted in the formation of a 4.5nm smooth, amorphous carbide layer in the carbon-implanted region. However, annealing at a higher temperature, 1000°C, lead to the formation of a rough poly-crystalline carbide layer. The multilayers were characterized by grazing incidence X-ray reflectometry and cross section TEM. [Copyright &y& Elsevier]

Abstract: Reported is a computational and chemical analysis of near normal incidence reflective multilayer optics for 6.7nm wavelength applications in e.g. the Free Electron Laser FLASH and next generations of EUV lithography. We model that combinations of B or B4C with La offer a reflectivity of ~70%. The small reflectivity bandwidth poses problems in applications, but it can be significantly improved by replacing La with Th or U. Grazing incidence X-ray reflectometry, cross-section TEM, and in-depth XPS analysis of B/La and B4C/La multilayers reveal chemical reactivity at the interfaces. Significant LaB x interlayer formation is observed in especially B/La multilayers, stressing the relevance of interface passivation. We propose nitridation of the interfaces, which mitigates interlayer formation and simultaneously increases optical contrast. [Copyright &y& Elsevier]

Abstract: In this work we present a study of surface roughness development at the molybdenum-on-silicon and silicon-on-molybdenum interfaces in Mo/Si multilayers as employed in Extreme UV lithography. Thin Mo/Si multilayers, with layer thicknesses of 3–5 nm, were deposited using electron beam evaporation. The effect of ion treatment on the surface roughness was studied by X-ray reflectometry and transmission electron microscopy. Without ion treatment we observed build up of correlated roughness. The roughness development is shown here to depend strongly on the thickness of the crystalline Mo layer. Independent of the Mo ratio in a period, we show that a minimal amount of ion treatment is required to smoothen the multilayer roughness, which is also confirmed by EUV reflectivity measurements. At high ion energies the layers become smoother due to a larger ion penetration depth. The higher penetration depth is also shown to initiate additional interdiffusion and structural changes at buried interfaces. [Copyright &y& Elsevier]

Abstract: In this paper, we present an experimental study on the structural and crystalline properties of electron beam evaporated Mo/Si multilayers. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) experiments were used to characterize the crystalline nature of Mo and Si. TEM and XRD show that Si grows amorphous, while Mo clearly crystallizes. The Mo crystallites show no preferred growth orientations and a columnar growth mode, with crystallite sizes limited by the Mo layer thickness. From samples with low Mo content, we show that crystallization of Mo starts directly at the Mo/Si interfaces, with the formation of a Mo3Si compound. The crystallite lattice strains that develop during Mo-on-Si growth due to lattice mismatches, will add to the macroscopic multilayer stress. By comparing Mo lattice strains derived from XRD with changes in substrate curvatures, as determined by interferometry, we show that compressive and tensile substrate deformations are predominantly caused by the internal crystallite strains. [Copyright &y& Elsevier]

Abstract: To improve the thermal stability of Mo/Si multilayers, a novel method to form carbide based diffusion barriers, produced by the implantation of Si with CH x + ions, has been developed. The multilayers were grown by e-beam evaporation, while CH x + ions were implanted at the Mo/Si interfaces, using a Kaufman ion source with a Ne/CH4 gas mixture. Energies were varied from 300 to 1000eV. The growth as well as the implantation procedure were monitored by in situ X-ray reflectometry. Auger Electron Spectroscopy was used to characterize the surface composition before and after CH x + ion implantation. The shift of the Si LVV Auger peak revealed the formation of SiC. Ex situ X-ray reflectometry showed a thermal stability of both the reflectivity and the multilayer period up to 430K. [Copyright &y& Elsevier]