Evolution Of Film Morphology Research Articles

A numerical study on the effect of mobilities and initial profile in thin film morphology evolution

This paper presents a numerical method for simulating the morphology evolution of elastically stressed thin film due to surface diffusion and evaporation/condensation. Elastic stress field is solved by using boundary element method and morphology evolution is simulated by using an integral formulation, which does not require the calculation of surface curvature and has weaker requirement on the smoothness of surface than the formulation based on differential equations. As a model problem, surface morphology evolution of a stressed thin film is simulated to explore the similarity and difference between the surface grooves induced by surface diffusion and evaporation/condensation, the effect of the mobility ratio of two processes when they are concurrent, and the dependence of surface kinetic pathway on its initial profile. It is found that the grooves induced by surface diffusion and evaporation/condensation have different surface features: when two processes are concurrent but surface diffusion process is dominant, increasing the mobility of evaporation/condensation increases the time and groove depth needed to form surface cusps; an initially cracked surface could approach a flat surface first, then after a long slowly evolving period, it gradually develops sharp tips on the surface again. Simulations show that excessive surface area, due to small cracks, notches or other surface defects, could significantly delay the development of surface instability.

Interplay of Physical and Chemical Aspects in the PECVD and Etching of Thin Solid Films

AbstractFor Abstract see ChemInform Abstract in Full Text.

Water-induced morphology evolution of block copolymer micellar thin films

Morphology evolution of diblock copolymer polystyrene- block-poly(4-vinylpyridine) (PS- b-P4VP) micellar thin film in the presence of water was investigated. Surface holes with nanoscale cavities in hexagonal order could be induced by water treatment for certain periods. The nanoscale surface cavities could be transformed into isolated nanospheres in a dry environment or back to protruding densely packed spheres by toluene (a selective solvent for PS coronae) treatment. The morphology evolution of micellar thin film strongly depended on the slow evaporation of toluene solvent, the swelling of P4VP cores in the humid environment, and the subsequent movement of PS chains induced by air and toluene. The incompatibility between solvent and block, and that between the unlike blocks also played an important role in the morphology evolution.

Effect of ion irradiation on the evolution of Pt film morphology

Atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis have been used to characterize ion-irradiated-and-annealed surface structures of Pt thin films deposited on SiO 2 glass substrates. The surface morphology of the Pt films is found to be strongly dependent on ion irradiation conditions. A Pt film composed of grains of approximately 1 μm diameter with a smooth surface is successfully prepared by an appropriate combination of ion irradiation and annealing. The Pt film shows a preferential (1 1 1) orientation parallel to the substrate surface.

AFM Observations of Phase Transitions in Molecularly Thin Films of a Three-Ring Bent-Core Compound

Submonolayer thin films of a three-ring bent-core (or banana-shaped) compound, m-bis(4-n-octyloxystyryl)benzene (m-OSB), were vacuum-deposited on a mica surface, and a spontaneous transition from monolayer films to bilayer crystals was observed at room temperature, which was ascribed to the specific molecular shape and polar layered packing of the bent-core molecules [Tang et al. J. Phys. Chem. B 2004, 108 (34), 12921-12926]. The crystal nucleation and growth from the monolayer films as well as the melting phase transition from the bilayer crystals were investigated using atomic force microscopy (AFM). It was shown that after initial nucleation, the crystal growth was achieved through three pathways: direct absorption of molecules from monolayer films, molecular cluster diffusion, and quasi-Ostwald ripening. When annealing the bilayer crystals at elevated temperatures, morphological change from a bilayer to a monolayer was observed, and some new islands with fingerlike patterns were formed during this process, which resulted from a diffusion-controlled growth of the molten molecules. In general, the high-resolution AFM in combination with the molecularly thin m-OSB films provided us with direct visualization of nucleation, crystal growth, melting, and film morphology evolution on the mesoscopic scale, which are of fundamental interest from the theoretical viewpoint and are of central importance for the control of interfacial properties in practical applications.

Substrate strain effect of EuBa 2Cu 3O 7− δ film: interplay between dislocations, precipitates and superconductivity

Our previous study showed that there is always a substantial resistive tail below the bulk T C of EuBa 2Cu 3O 7− δ and SmBa 2Cu 3O 7− δ (RBCO) films deposited on nearly perfect lattice matched SrTiO 3 (STO) substrates, which is in contrast to the same films deposited on less well-matched substrates, e.g., LaAlO 3 (LAO), under similar conditions. Although the lattice match is poorer, the latter films have a sharp resistive transition without any tail. The present study examines the evolution of precipitate density and intergranular coupling with increasing film thickness, revealing that dislocations induced from the release of strain affect the precipitation of off-stoichiometric phases. We propose a model that indicates induced dislocations attract off-stoichiometric phases and thus lead to tower-like precipitates. The precipitates segregate the potential impurities out from grain boundaries. Therefore, the intergranular coupling of RBCO film grown on LAO improves with increasing thickness. Meanwhile, in the absence of precipitates, off-stoichiometric materials in the film on STO coat each columnar grain. This model is consistent with the observed evolution of film morphology, T C and J C with thickness, and the theoretical fitting of the measured χ( t) curves.

Effect of working conditions on the morphology of electrosynthesized polyfuran

AbstractThe influence of electrolyte and deposition potential on polyfurane doped/undoped electrogenerated films was analyzed by potentiodynamic profiles and current–time transients. The films were formed on platinum electrodes from the monomer and tetrabutylammonium hexafluorophosphate, tetrabutylammonium tetrafluoroborate, or tetraethylammonium perchlorate in acetonitrile. Results were also discussed with the aid of X‐ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), and primarily by scanning electron microscopy (SEM). It was shown that there is some oxygen contamination not only after ClO4 doping. However, it was shown by XPS and EPMA that COC bonds are present in the films, which confirmed that there was no destruction of the furan ring during electropolymerization. SEM study showed film morphology evolution with monomer concentration, and with the electrolyte or the dopant used. The undoping effect was also visualized, showing that doped polyfuran was more homogeneous than the respective undoped deposits. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1346–1354, 2004

Interplay of physical and chemical aspects in the PECVD and etching of thin solid films

The deposition and etching of thin solid films by means of weakly ionized plasmas is discussed here with the aim of stressing the interlink between the involved physical events and their related chemical reactions. This is particularly important in two situations. First in the gas phase, where the concentration, energy, and reactivity of ions, electrons, radicals, and excited molecules generated by electronic reactions influence the electromagnetic field employed to sustain the plasma, the electron energy distribution function, the time evolution and spatial distribution of the electronic temperature and density. Then secondly on the film surface the ionic surface bombardment has a significant impact on the surface chemistry, which eventually determines the film morphology. In this work we report on the progress of theoretical approaches that correctly describe complex systems where chemical and physical aspects are strongly coupled. We show how it is now possible to formulate detailed plasma reactor models that can predict the concentration of the different charged and neutral species in the gas phase, their gas phase and surface reactivity, growth and etch rates, and the film morphological and compositional evolution. The modern approach takes advantage of the progress in computational chemistry and molecular dynamics to calculate the unknown parameters needed as input to the reactor model. Some examples where the mentioned approach is applied are given.

A Multiscale Model of the Si LPCVD Process

ABSTRACTThe Low Pressure Chemical Vapor Deposition of Si from SiH4 is an industrial process that can be used to deposit epitaxial Si at relatively low surface temperatures. Multiscale models are necessary in order to tune the operating conditions to optimize the quality of the deposited materials. In this work we present a multiscale approach meant to describe the film morphological evolution at different time and length scales. The reactor fluid dynamics and overall mass and temperature balances are solved with the finite element method. The morphological evolution of the film is investigated with 3D kinetic Monte Carlo. We have systematically investigated the dependence of the growth morphology from temperature, pressure and gas phase composition (SiH4/H2 ratio) with the aim of determining the operating parameters window that can lead to the best film morphology. We found that the presence of a significant amount of hydrogen on the surface can significantly influence the surface morphology. In particular hydrogen can be considered as the principal responsible of the transition from an order terrace step flow growth regime, which prevails at high temperatures, to a disordered 3 dimensional growth regime. It is also worth noting that our KMC simulations show that the hydrogen surface chemistry active at low temperatures is probably richer than expected, since the formation of a significant number of island on the surface dramatically increases the concentration of steps, and thus the variety of configurations by which two adsorbed H atoms can interact.

Low-energy electron irradiation of fullerene films formed on Si(111)-(7×7) surfaces

C 60 films of 4–6 ML formed on Si(111)-(7×7) substrates were irradiated by field-emission (FE) electrons extracted at 15–80 V from probe tips of a scanning tunneling microscope (STM), and resulting evolution of film morphology was observed by the STM. At low extraction voltage, FE electrons stimulated polymerization of adjacent molecules and long-lasting migration of C60. At extraction voltage above ∼40 V, carbon spheroids less than 2 nm in height were created as a result of diffusion and coalescence of C60 fragments produced by electronic excitation.

Kinetics of submonolayer epitaxial growth

Molecular beam epitaxy is an important method for growing thin-films and nanostructures. One of the scientific challenges is to understand the fundamental processes that control the evolution of thin film structure and morphology. The results of kinetic Monte Carlo simulations carried out to study the dependence of the submonolayer scaled island-size distribution on the critical island-size are presented and compared with experiments. A recently developed method which involves a self-consistent coupling of evolution equations for the capture-zone distributions with rate-equations for the island-size distribution is also described. Our method explicitly takes into account the existence of a denuded (“capture”) zone around every island and the correlations between the size of an island and the corresponding average capture zone, and has been used to develop a quantitative rate-equation approach to irreversible submonolayer growth on a two-dimensional substrate. The resulting predictions for the capture-zones, capture numbers, and island-size distributions are in excellent agreement with experimental results and kinetic Monte Carlo simulations.

Morphological and phase evolution of nano-crystalline carbon films with a predominant diamond character

Abstract In the present work, the evolution of nano-diamond films deposited by the glow discharge chemical vapour deposition method onto silicon substrates as a function of time were studied by various complementary techniques. Our analysis showed that prior to formation and growth of continuous films of a predominantly nano-diamond character, a graphitic phase is formed. This graphitic film displays a preferred alignrnent of its basal planes perpendicular to the silicon substrate interface. The nano-diamond character of the films gradually evolves reaching a maximum value of ∼80% for film thickness larger than ∼0.5 μm. It was found that the appearance of the nano-diamond phase is initially accompanied with an increase in surface roughness which decreases with film growth. It was determined that the continuous nano-diamond films are composed of diamond nano-crystallites, ∼5 nm in diameter alongside a sp2 bonded amorphous carbon phase. Most likely the amorphous carbon component in the films exists at the nano-diamond grain boundaries. The phase and morphological evolution of the films were investigated, with nanoscopic resolution, by a number of complementary spectroscopy and microscopy techniques: near edge X-ray adsorption fine structure, scanning electron microscopy and atomic force microscopy, high-resolution transmission electron microscopy and X-ray diffraction.

Nanoscale pattern formation in Pt thin films due to ion-beam-induced dewetting

Atomic force microscopy is used to characterize the evolution of film morphology produced by heavy-ion bombardment. Pt films, 3 and 5 nm thick, are deposited on SiO2 substrates and subsequently bombarded by 800 keV Kr+. Ion doses of >2×1014 initiate pattern formation and the dewetting of Pt films from the substrate. The film morphology becomes increasingly disconnected with increasing dose; at the highest doses, (∼2×1016 cm−2), isolated nanoparticles are formed with a uniform spacing. The results are explained by the nucleation of bare substrate patches and subsequent coarsening of the morphology by the molten zones created by individual Kr+ impacts.

Roughness evolution of Nb films with thickness

Abstract The morphology of Nb films with thickness ranging between 10 and 1000 nm deposited by rf sputtering and the electron cyclotron resonance (ECR) techniaue was investigated by scanning probe microscopy (SPM). The roughness of the films increases with increasing thickness following a power law with an exponent of 0.26 and 0.6 for conventional sputtering and the ECR techniaue respectively. Film surface features evaluated by the autocorrelation function of the SPM images show a similar dependence on the thickness with an exponent of 0.25 independent of the deposition system. Evolution of Nb film morphology deposited by rf sputtering is compatible with a surface diffusion-driven growth process where desorption is negligible, while films deposited by the ECR techniaue show a more complex behaviour. SUMMARY The surface morphology of Nb thin films grown with different deposition systems was analysed by AFM and STM. The roughness and the surface hills of films deposited by ECR are three to four times lower ...

Palladium composite membranes by electroless plating technique: Relationships between plating kinetics, film microstructure and membrane performance

Thin supported palladium membranes were prepared using electroless plating technique. The intrinsic plating kinetics were determined for hydrazine-based palladium plating baths. Mathematical models were developed to predict film thickness and plating rate as a function of plating parameters (i.e., reactant concentrations, temperature and time). Analyses of film surface microstructure indicate that grain structure is dependent on both plating chemistry and plating rate. The evolution of film morphology during electroless plating was also investigated. Hydrogen permeation study demonstrated that film structure has a significant influence on the permeation performance of the palladium membrane.

Influence of crystallization kinetics on texture of sol–gel PZT and BST thin films

The evolution of morphology of sol–gel PZT and BST thin films during rapid thermal annealing (RTA) is investigated by recording of elastic light scattering data in reflected mode. The analysis of film morphology and texture evolution obtained by XRD reveals the dependence of crystallization kinetics on the annealing conditions. The evolution of film morphology during the transition to the perovskite phase is analysed by the time dependence of fractal dimensionality. The parameters characterizing the kinetics of the transformation to the perovskite phase are extracted by mathematical treatment of experimental data. A mechanism for texture formation is proposed.

Study of Electrochemical Deposition of Copper and Microstructure Evolution in Fine Lines

ABSTRACTAs computer chip technologies evolve from aluminum-based metallization schemes to their copper-based counterparts, Electrochemical Deposition (ECD) is emerging as a viable deposition technique for copper (Cu) interconnects. This paper presents the results of a first-pass study to examine the underlying mechanisms that control ECD Cu nucleation, growth kinetics, and post-deposition microstructure evolution (self-annealing), leading to the development and optimization of an ECD Cu process recipe for sub-quarter-micron device generations. The influence of bath composition, current waveform, type and texture of Cu seed layer, and device feature size (scaling effect) on the evolution of film texture, morphology, electrical properties, and fill characteristics was investigated using a manufacturing-worthy ReynoldsTech 8″ wafer plating tool. Resulting films were analyzed by X-ray Diffraction (XRD), four-point resistivity probe, Focused-Ion-Beam Scanning Electron Microscopy (FIB-SEM), and Atomic Force Microscopy (AFM). These investigations identified an optimized process window for the complete fill of aggressive device structures with pure Cu with resistivity ∼ 2.0 μΩ-cm and smooth surface morphology.

Study of Electrochemical Deposition of Copper and Microstructure Evolution in Fine Lines

AbstractAs computer chip technologies evolve from aluminum-based metallization schemes to their copper-based counterparts, Electrochemical Deposition (ECD) is emerging as a viable deposition technique for copper (Cu) interconnects. This paper presents the results of a first-pass study to examine the underlying mechanisms that control ECD Cu nucleation, growth kinetics, and post-deposition microstructure evolution (self-annealing), leading to the development and optimization of an ECD Cu process recipe for sub-quarter-micron device generations. The influence of bath composition, current waveform, type and texture of Cu seed layer, and device feature size (scaling effect) on the evolution of film texture, morphology, electrical properties, and fill characteristics was investigated using a manufacturing-worthy ReynoldsTech 8” wafer plating tool. Resulting films were analyzed by X-ray Diffraction (XRD), four-point resistivity probe, Focused-Ion-Beam Scanning Electron Microscopy (FIB-SEM), and Atomic Force Microscopy (AFM). These investigations identified an optimized process window for the complete fill of aggressive device structures with pure Cu with resistivity ∼ 2.0 µΩ-cm and smooth surface morphology.

Spectroscopic light scattering for real-time measurements of thin film and surface evolution

We describe a light scattering technique for measuring the real-time evolution of thin film and surface morphology. By using spectroscopic detection, the technique requires no motion of the sample during the measurement, which makes it compatible with many processing geometries. Results from the growth of strained heteroepitaxial layers of SixGe1−x on Si(001) are presented to demonstrate the technique.

UHV-CVD heteroepitaxial growth of Si 1− xGe x alloys on Si(100) using silane and germane

In this paper, we investigate the growth rate and strain relaxation of Si 1− x Ge x layers grown on Si substrates by UHV-CVD. The Si 1− x Ge x growth rate is found to exhibit two different behaviors as a function of growth temperature. Above the temperature corresponding to hydrogen desorption ( T H), the SiGe growth rate first decreases with x, and finally becomes almost independent of x at higher values of x. Below T H, the SiGe growth rate first increases with x, then shows a maximum and finally becomes almost independent of x at higher values of x. Using in-situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy and photoluminescence, we have clearly identified two distinct mechanisms for strain relaxation as a function of Ge content: at x=0.15 strain is relaxed by nucleation of misfit dislocations while the film surface remains smooth throughout growth and relaxation process. The introduction of dislocations is found to occur before lattice relaxation. At x=0.22, strain is first relaxed via formation of coherent islands before reaching the equilibrium critical thickness for dislocation nucleation. We also show that in-situ RHEED is a powerful technique to probe the evolution of film morphology in an ultra high vacuum chemical vapour deposition system. © 1997 Elsevier Science S.A. All rights reserved.