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The functionality and reliability of nano-multilayered devices and components are largely affected by the stress evolution during fabrication, processing, and operation. The impact of thermal treatment on the stress state and evolving microstructure of Cu/W nano-multilayers, as deposited on different substrates (i.e., Si(001), Al2O3-C, and Al2O3-R) by magnetron sputtering, was investigated by in-situ high temperature X-ray diffraction and high-resolution scanning electron microcopy. The as-deposited Cu and W nanolayers exhibit an out-of-plane orientation relationship according to Cu 〈111〉|| W 〈110〉. On the Al2O3-C and Al2O3-R substrates, the Cu/W nanomultilayers also develop a pronounced in-plane texture given by Cu {111} 〈101〉 || W {110} 〈001〉. The stress state of the Cu nanolayers in the as-deposited state and upon heating, investigated ex-situ, is largely imposed by the accumulated stresses in the much stiffer W nanolayers. In the as-deposited state, the W nanolayers exhibit a much larger in-plane compressive stress than the Cu nanolayers (i.e., -3.5 GPa versus -1.5 GPa), which both mainly originate from growth stresses generated during the deposition process. The growth stresses in the as-deposited Cu nanolayers are relaxed after annealing at 500 °C. Relief of compressive stresses in the W nanolayers is accompanied by grain coarsening which only occurs upon degradation of the nano-multilayered structure. The degradation of the periodic layer structure proceeds in the range of 750-900 °C and is independent of the substrate. [ABSTRACT FROM AUTHOR]

During the deposition of polycrystalline thin films, often intrinsic compressive stresses develop, which reversibly change in tensile direction once the deposition process is interrupted. Up to date, the underlying mechanism of such reversible stress changes during growth interruptions have been controversially discussed, mainly because the correlations between the growth conditions, the developing film microstructure and the reversible stress change were still largely unclear. The present study has experimentally established the separate effects of the pre-interruption deposition rate and the average lateral film grain size on both the magnitude and the kinetics of the reversible tensile stress rise during polycrystalline film growth interruption. To this end, real-time in situ substrate-curvature measurements were performed during polycrystalline Ag growth and upon subsequent growth interruptions for well-defined and controlled adjusted microstructures. It is shown that the magnitude of the reversible tensile stress rise during growth interruption is predominantly governed by the grain-boundary density, while the rate of the tensile stress rise during growth interruption increases with increasing pre-interruption deposition rate and increasing (lateral) Ag grain size. These phenomena can be rationalized by taking deposition-rate and lateral-grain-size dependent surface morphological developments into account. [ABSTRACT FROM AUTHOR]

The evolutions of the surface stress of Si(111)-77, Si(100)-21, and a-Si surfaces upon oxygen exposure at pO2 = 1 x 10-4 Pa and room temperature have been investigated in a comparative manner using a specimen-curvature based technique. To this end, a generally applicable, dedicated set of experiments has been devised and performed to deduce and correct for the surface stress change owing to oxygen reaction(s) at the (poorly-defined) back face of the specimen only. On this basis, it could be demonstrated that exposure of clean Si(111)-77, Si(100)-21 and a-Si surfaces to pure oxygen gas results in compressive surface stress changes for all three surfaces due to the incorporation of oxygen into Si backbonds. The measured surface stress change decreases with decreasing atomic packing density at the clean Si surfaces, which complies well with the less-densily packed Si surface regions containing more free volume for the accommodation of adsorbed O atoms. [ABSTRACT FROM AUTHOR]

Real-time in situ spectroscopic ellipsometry and in situ, angle-resolved x-ray photoelectron spectroscopy (AR-XPS) have been applied to establish the relationships between the growth kinetics and the developing microstructure of ultrathin (<3 nm) oxide films grown on clean Al–1.12 at. % Mg alloy surfaces by thermal oxidation in the temperature range T=300–485 K. To this end, procedures for the depth-resolved quantitative AR-XPS analysis of ultrathin, multiple-element, and/or multiphase oxide overgrowths on binary alloy surfaces were developed. As a result, the relationships between the relative depth distributions of Al and Mg in the developing oxide films, the oxide-film growth kinetics, and the oxidation-induced compositional changes in the AlMg alloy substrate could be established as a function of the oxidation conditions. [ABSTRACT FROM AUTHOR]

The thermodynamic and kinetic background of the stability of ultrathin (<3 nm) amorphous Al2O3 overgrowths on Al{111}, Al{100}, and Al{110} substrates was investigated by thermal oxidation of the bare substrates in pure oxygen gas for oxidation times up to 6000 s in the temperature range of T=350–650 K. The microstructural evolutions of the developing oxide films were analyzed by angle-resolved x-ray photoelectron spectroscopy, low energy electron diffraction, and high-resolution transmission electron microscopy. For sufficiently small thicknesses, stable amorphous Al2O3 films form on all substrates. The critical thickness values beyond which a crystalline state for the Al2O3 film is thermodynamically preferred can be reliably calculated provided that a layer-by-layer mode of oxide-film growth occurs. With increasing temperature, a transition from a layer by layer to an island-by-layer type of oxide growth mode occurs and, consequently (tensile), growth strain in a crystalline Al2O3 overgrowth can be more relaxed by lateral extension of the oxide islands, which results in a reduction of the critical thickness for the amorphous-to-crystalline transition. Oxygen incorporation in the metal substrate at the onset of oxidation, in particular, at higher temperatures and for the less densely packed surfaces of the metal substrate, can provide a mechanism for easy nucleation of crystallization at the metal/oxide interface of the amorphous oxide film of thickness larger than the critical thickness. [ABSTRACT FROM AUTHOR]

A procedure has been developed to determine the growth kinetics of thin (<3 nm) oxide films on bare binary alloys from the measured changes of the ellipsometric amplitude-ratio and phase-shift dependent parameters, ψ and Δ, versus wavelength, as function of oxidation time, as recorded by real-time, in situ spectroscopic ellipsometry. The approach has been applied to the dry, thermal oxidation of Mg-based MgAl substrates of low (2.63 at. %) and high (7.31 at. %) bulk Al content at 304 K within the partial pressure of oxygen range of 10-6–10-4 Pa. Various models have been developed to describe the time dependences of the spectra of ψ(λ) and/or Δ(λ) for the initial and subsequent stages of oxidation. It followed that the initial oxide-film growth kinetics can be accurately described by adopting a three-node graded oxide layer using the Maxwell-Garnet effective medium approximation to assess the optical properties of the compositionally inhomogeneous, Al-doped MgO film developing on the MgAl alloy surface. The specific complications that arise in the ellipsometric analysis of the oxidation of binary alloys (as compared to that of pure metals), such as due to the concurrent processes of selective oxidation and (oxidation-induced) chemical segregation, have been discussed. [ABSTRACT FROM AUTHOR]

Angle-resolved x-ray photoelectron spectroscopy (ARXPS) and in situ spectroscopic ellipsometry have been used to investigate the initial oxidation of polycrystalline zirconium at room temperature in the partial oxygen pressure range of 1.3×10-7–1.3×10-4 Pa. Detailed quantitative analysis of the measured Zr 3d ARXPS spectra of the oxidized metal allowed separation of the intrinsic and extrinsic metallic and oxidic contributions to the spectra. It was shown that, in addition to the metallic contribution from the substrate and the oxidic contribution from stoichiometric ZrO2, two additional suboxidic components are contained in the measured Zr 3d spectra of the oxidized Zr metal. As evidenced by angle-resolved XPS and in situ ellipsometry, both of these components can be attributed to a gradient of Zr enrichment in the region of the oxide film adjacent to the metal/oxide interface (with the highest Zr enrichment at the metal/oxide interface). Investigation of the oxide-film growth kinetics at various pO2, as determined independently using both techniques, showed the occurrence of an initial regime of very fast, electric-field-controlled growth, followed by a much slower oxidation stage. As a result, an, on average, nonstoichiometric oxide film develops. The observed effect of the pO2 on the low-temperature oxidation of Zr has been discussed in terms of the relationship between the fraction of coverage of the surface with physi- and chemisorbed oxygen and the applied pO2. [ABSTRACT FROM AUTHOR]

The growth kinetics and mechanisms of thin aluminum-oxide films formed by the dry, thermal oxidation of a bare Al(431) substrate at a partial oxygen pressure of 1.33 × 10[sup -4] Pa in the temperature range of 373-773 K were studied using x-ray photoelectron spectroscopy. The initial oxidation of the bare Al substrate proceeds by an island-by-layer growth mechanism, involving the lateral diffusion over the bare Al substrate surface of mobile oxygen species. At low temperatures (T ≤ 573 K), an amorphous oxide film develops that attains a limiting (uniform) thickness. At high temperatures (T>573 K), growth is not impeded at a limiting thickness. Kinetic analysis established the occurrences of two different oxide-film growth regimes: an initial regime of very fast oxide-film growth and a second, much slower oxidation stage that is observed only at T > 573 K. These results could be discussed in terms of electric-field controlled, interstitial, outward transport of Al cations through a close packing of O anions in the amorphous films, and inward diffusion of O along grain boundaries in the crystalline films, respectively. For the electric-field controlled Al cation motion, a value of 2.6 eV was determined for the rate-limiting energy barrier, which is located at the metal/oxide interface. This corresponds with a Mott potential of -1.6 V. [ABSTRACT FROM AUTHOR]