This paper provides a thermodynamic analysis of hole and hillock growth in stressed thin films in simplified geometries. Two limiting cases were considered. In the first, matter is transported to (from) the growing hillock (hole) from (to) the surface of the film. In the second case, the material transported to (from) the growing hillock (hole) comes from (goes to) the interior of the film in the vicinity of the hillock (hole). When bulk relaxation is dominant, hillock growth is favored by a compressive stress in the film and hole growth is enhanced when the film is in tension. This is the commonly observed situation. On the other hand, when surface relaxation effects dominate, hillocks and holes can grow in either tension or compression.

Transmission electron microscope observations of microstructural development in thin films of gold are presented. In a sequential annealing experiment, we find that individual grains are constantly rotating and that this contributes to the rearrangement of grain boundaries by allowing their individual energies to vary.

This paper reports a study in which a rough tungsten surface was prepared by chemical vapor deposition of tungsten on a tungsten ribbon. The samples were then heated to study the smoothing behavior of the rough surface. The results show that at 1600°C the surface becomes smooth after approximately five to ten hours. At 2400°C the surface becomes smooth within 15 minutes.

Platinum thin films were deposited on SiO2/Si(100) by metalorganic chemical vapor deposition using Pt(acetylacetonate) and Pt(hexaflouroacetylacetonate) as precursors. The films were characterized in terms of orientation, surface roughness and morphology. As expected, Pt(111) was the preferred orientation. Higher substrate temperatures led to higher growth rates and increased surface roughness. The presence of oxygen during deposition decreased the minimum substrate temperature required for platinum deposition, indicating that oxygen played a role in the decomposition of these metalorganic compounds. Annealing platinum films at 550°C in an oxygen ambient resulted in hillock formation. Resistivity measurements showed that films deposited without oxygen were more resistive. Conformal coverage of platinum on patterned SiO2/Si substrates was investigated, and a side wall film thickness to top film thickness ratio of 0.6 for growth at 400°C was obtained. These Pt films produced by MOCVD displayed greater surface roughnesses than films grown by evaporation or sputtering.

Sputtered Mo films with a thickness of 2μm or greater have been previously shown by xray and TEM studies to grow with strong in-plane and out-of-plane textures under dynamic deposition conditions. In this work, the geometric conditions and mechanisms causing preferential grain alignment in the plane of growth for sputtered Mo films, with a nominal thickness of 2μm, were explored. Four different deposition configurations, obtained by varying the parameters such as the deposition angle and the rotation speed of the substrates, were used in order to modify the texture as studied by x-ray and SEM techniques. While a [110] type out-of-plane texture was observed for all four deposition configurations, a (110) type in-plane texture, and the corresponding grain alignment in the plane of growth, was observed only when the flux of adatoms was hitting the substrates at an oblique angle. The texture characteristics and the microstructure of the Mo films, as analyzed using the pole figure x-ray and SEM techniques, were observed to be very similar for films deposited on three different substrates, namely the Si(100) and Ni3Al(321) single crystals, and laboratory grade glass slides. The in-plane texture development under oblique deposition conditions was proposed to be due to a combination of two mechanisms, namely the preferential resputtering of some of the grains normal to and in the plane of growth caused by the higher energy adatoms in the flux, followed by termination of the preferentially sputtered grains due to geometric shadowing.

Two dimensional non-equilibrium molecular dynamics simulations are performed to study microstructural evolution during the growth of polycrystalline thin films. Attention is focused on the interaction between grain boundaries and voids which form during deposition, and on the development of a preferred, crystallographic texture during film growth. In an intermediate temperature regime, where the film is cold enough to allow void formation but hot enough to allow grain boundary motion, boundaries move such as to attach themselves to voids as the voids form from depressions in the film surface. At lower temperatures, the boundaries have insufficient mobility to migrate toward the voids. At higher temperatures, films grow in the absence of voids. At low deposition kinetic energies, there is no tendency for polycrystalline films to develop a preferred texture. At moderate or high energy deposition kinetic energies, however, as in the case of magnetron sputtering, significant texture formation can result due to preferential (re)sputtering of atoms from the surface of grains with low-binding-energy exposed surfaces. Such preferential (re)sputtering provides a height advantage for grains possessing high-binding-energy exposed surfaces. The taller grains are seen to widen as deposition continues, resulting in the development of a preferred crystallographic orientation.

A simple process, involving a controlled temperature gradient on the surface of the substrate during the deposition of a thin film is described. This technique is similar to zone-refining but produces chains of impurity free grains. Simultaneously, dopants and other defects are confined to the grain boundaries separating two such chains. For a small temperature gradient only preferred orientation is obtained within a chain. For medium values of temperature gradient the grain boundaries within a chain are engineered to be either on a low energy coincidence site lattice (CSL) or a twin depending on the magnitude of gradient. For high magnitudes of temperature gradient, the chain is predicted to be a single crystal strip.

It is a well known fact that the properties and performance of polycrystalline materials, including polycrystalline thin films, are strongly affected by the grain structure. Therefore, in treating reactive phase formation in these films, it is (or it will inevitably be) necessary to quantify the grain structure of reactant and product phases and its evolution during the course of the reaction. Theoretical models and the conventional view of thin film reactions, however, have been largely extensions, to small and finite dimensions, of theories and descriptions developed for bulk diffusion couples. These models and descriptions primarily focus on the growth stage and to a much lesser extent on the nucleation stage. Consequently, these models and descriptions are not able to treat the development of product phase grain structure. Recent calorimetric investigations of several thin film systems demonstrate the importance of nucleation kinetics (and hence nucleation barriers) in product phase formation and provide quantitative measures of the thermodynamics and kinetics of formation of the product phases, thereby allowing some degree of comparison with reaction models. Furthermore, microstructural investigations of thin-film reactions demonstrate the non-planarity of the growth front and highlight the role of reactant-phase grain boundaries. In this paper, a summary of these experimental studies and recent theoretical treatments, which combine nucleation and growth in an integrated manner, is presented, with particular emphasis on the Nb/Al system. These experiments and models lead to a new view of reactive phase formation and grain structure evolution as one in which the latter is an integral part of the former. Based on this view, directions for future research are discussed.

Orientation selective grain growth in thin films arises due to anisotropy in materials properties. For continuous thin films, there are at least two orientation dependent driving forces for grain growth: (i) surface and interface energy anisotropy; (ii) strain energy anisotropy (both elastic and plastic). In fcc metals, the preferred growth of grains with (111) texture occurs due to their low surface and interface energy. Stresses in thin films arise during deposition and as a result of post-deposition annealing. A texture dependence of strain energy density arises in biaxially strained thin films due to anisotropy of elastic properties and/or orientation-dependent yield stresses. For most fcc metals, the strain energy driving force promotes the growth of (001) grains due to minimization of the combined elastic and plastic strain energy. The magnitudes of the orientation dependent driving forces for grain growth depend on the characteristics and processing conditions of the film and substrate. We have performed grain growth experiments for Ag films on single crystal Ni on MgO; Ag films on plasma-enhanced chemical vapor deposited (PECVD) SiO2 on MgO; Ag films on oxidized Si; and Ni films on oxidized Si. The texture resulting from grain growth in films of different thicknesses and deposited at different temperatures were determined, and the results are presented in the form of texture maps. The texture which dominates as a result of grain growth can be understood through the use of texture maps and compares well with analytic models for texture development during grain growth in thin films.

This paper outlines the use of the Principle of Virtual Motion and the Galerkin approximation to analyze surface diffusion phenomena. Various ideas are illustrated with an analysis of the evolution of a fiber of bamboo-like grain structure.

We employed a Monte Carlo technique to simulate the effect of (1) the anisotropic grain boundary energy in the film and (2) the large misfit between the film and substrate on the grain growth of [001] textured Yba2Cu3Ov7-x (YBCO) films. In terms of remaining grain boundaries of certain misorientations, the simulation results concur with the experimental observation of preferred grain orientations of YBCO on various substrates, such as (001) MgO and (001) Yttria stabilized Zirconia (YSZ). Three factors were identified to influence the grain growth of these [001] tilt boundaries in the simulation and could help to elucidate the origin of special misorientations observed experimentally. These are (1) the depth of local minima in boundary energy vs. misorientation curve, (2) the number of possible combinations of coincidence epitaxy (CE) orientations contributing to the exact misorientation for each of the high angle but low energy (HABLE) boundaries, and (3) the number of possible combinations of coincidence epitaxy CE orientations within the angular ranges near each of the HABLE boundaries.

Thin Nb films were deposited by MBE on (0001)α-Al2O3 in UHV. At a substrate temperature of 800°C, reflection high energy electron diffraction (RHEED) revealed that the film grew with the orientation relationship (planes of similar symmetry are parallel to each other): (0001)α-Al2O3 ‖ (111)Nb; [2110]α-Al2O3 ‖ [110]Nb. Investigations with conventional transmission electron. microscopy (CTEM) revealed that the film was not perfectly epitaxial after deposition. Small Nb grains with different orientations were embedded in the epitaxial Nb film. During annealing at temperatures well above the deposition temperature, secondary grain growth of the small embedded Nb grains occured, leading to a different epitaxial relationship between the Nb film and the sapphire: (0001)α-Al2O3 ‖ (110)Nb; [0110]α-Al2O3 ‖ [001]Nb.

The statistics of the distances among the nearest-neighbor nuclei developed at the initial stage of the electrolysis was analyzed using the example of the metal (Cu, Ag, Cd) electrocrystallization on the isotropic glassy carbon. It was confirmed that the most frequently met intemuclei distances tn that follow the progression equation tn = t1 · qn-1 with q≈1.4 form “structural spots” where they are located following each other in a strict sequence ti, t2 …. , tn,. It is found that the form of the “structural spots” is variable and the nuclei's density toward the border of the spot either is decreased or increased. The conditions of electrolysis under which the phenomenon of the nuclei statistically arranged order is not seen are also found.

Low temperature synthesis of BaTiO3 thin films was performed under hydrothermal conditions below 80°C. Titanium metal, polycrystalline titanium oxide, and polystyrene (coated with a metallo-organic titanium precursor by a sol-gel process) were used as substrate materials. The reactions between the substrates and aqueous Ba(OH)2 solution took place at different time intervals from 10 minutes to 48 hours. The formation mechanisms of BaTiO3 was investigated by electron microscopy techniques during the reaction sequence. It is proposed that the nucleation and growth of crystalline BaTiO3 occur within an amorphous intermediate phase on Ti-metal and polystyrene substrates. However, thin film of BaTiO3 does not form on the surface of the sintered polycrystalline TiO2 under similar reaction conditions.

The influence of controlled potential conditions on the structure and phases of BaTiO3 films grown on titanium by the hydrothermal-electrochemical method was studied. The experiments were conducted using a three electrode high pressure electrochemical cell in a 0.2 M Ba(OH)2 electrolyte at 150 °C. The spontaneous initial nucleation linked to pure hydrothermal BaTiO3 formation was inhibited by cathodically protecting the titanium electrode since its immersion in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. The growth of tetragonal BaTiO3 was achieved combining the initial inhibition of the pure hydrothermal growth, followed by nucleation under controlled potentiostatic conditions.

Thin, disordered interlayers were used to enhance the nucleation of Si3N4. Continuous crystalline films were formed at relatively low temperatures (<1250°C) by using an amorphous, Sirich interlayer. The interlayer was produced by varying the CVD conditions (i.e., by using multistep processing). Samples were characterized with XPS, SEM, and TEM with concurrent EELS. The results indicate that the nucleation of crystalline material is very sensitive to the structure and composition of the disordered interlayers. Also, the structure and composition of the interlayers evolve during growth, such that crystalline material only nucleates when the interlayer provides favorable conditions.

Selective solid phase crystallization for control of grain size and location in polycrystalline thin Ge films on amorphous silicon dioxide substrates is described. The approach consists of selective solid phase crystal nucleation via an alloy reaction at predefined nucleation sites, which consist of metal islands deposited on top of the amorphous Ge film, followed by lateral solid phase epitaxial growth. Grain sizes as large as 30 μm have been achieved in 50 nm thick Ge films at temperatures less than 475 °C.

Mo films are deposited on various glass substrates using the sputtering technique. The film stress and texture are greatly affected by the substrate materials. For the films grown on borosilicate glass both DC and RF sputtering may produce films with desirable properties. However, the films with compressive stress can be deposited on sodalime glass substrates only by RF sputtering. Preferred orientations are (211) and (110) for the film grown on borosilicate glass substrate and the film grown on sodalime glass substrate, respectively.

The magnitude of the average stress in a thin film can be obtained by measuring the curvature of the film-substrate couple. However, the details of the strain distribution, as a function of depth through the thickness of the film, can have important consequences in governing film quality and ultimate morphology. A high-resolution x-ray diffraction method was used to determine the depth dependence of strain in a textured Mo film, with a nominal thickness of 260 nm, which was deposited by planar magnetron sputtering onto Si (100) substrates. The principal strains, resolved onto a laboratory reference frame, displayed a negligible gradient in the azimuthal directions (x and y), but displayed a large gradient in the direction normal to the film (z). A similar trend was previously observed for a 100 nm polycrystalline film, but the magnitude of the normal strain very near the free surface was about a factor of 2 less. The increase in the normal strain may be due to the development of a preferred growth direction and grain facetting. A linear elastic model was also used to determine the strains in successive slabs of the film, where strain variations between slabs were indicated.

The steady-state creep response of multilayered polycrystalline materials subjected to cyclic variations in temperature is analyzed. The approach presented here is capable of predicting the evolution of curvature, the thermal stresses, and the dominant deformation mechanisms at any through-thickness location of each layer for prescribed layer geometries and thermo-mechanical properties of the constituent layers. The Al-Al2O3 model system is considered, where the dominant relaxation mechanism in Al is studied as the layer thickness is systematically varied. Creep due to grain boundary diffusion is found to become more significant in thin layers with a three-dimensional equiaxed grain structure. The effects of columnar grain structure in Al thin films on the thermal cycling response are also discussed.