Microstructure Evolution Of Films Research Articles

Investigations of transient phase formation in Ti/Si thin film reaction

The analysis of temperature and time dependence of the Ti film microstructure evolution in Ti/Si thin films indicates Si diffusion occurs before any crystal phase is formed. Diffusion occurs first in Ti grain boundaries and then, within the grains. Ti5Si3 has been identified as a transient phase forming before C49 TiSi2 grows. Ti5Si3 only grows in isothermal runs in a narrow range of annealing temperatures (412–434 °C in our study). It has not been observed in temperature runs in which C49 TiSi2 forms. The mechanisms of Ti5Si3 formation and transformation into C49 have been found to be diffusion limited. Phases of alloyed Ti, amorphous silicide, Ti5Si3, and C49 TiSi2 have been simultaneously observed. The lifetime and the volume fraction of the initial metal layer transformed into Ti5Si3 are naturally tightly temperature dependent.

Imperfect wetting of vapor-deposited thin films: Monte Carlo simulations and nucleation model

In this paper we discuss atomistic Monte Carlo simulations of thin film microstructure evolution. We discuss physical vapor deposition, and are primarily concerned with the nucleation and coalescence of three-dimensional islands and their effect on film morphology. We discuss some fundamental issues associated with thin film formation, together with an assessment of the sensitivity of the film morphology to the deposition conditions and materials properties. In order to allow rapid assessment of the deposition conditions, we propose a simple analytical model that retains most of the essential physical parameters and properties.

Evolutionary phase diagrams for the deposition of silicon films from hydrogen-diluted silane

Phase diagrams that describe plasma-enhanced chemical vapor deposition (PECVD) of Si films at low substrate temperature (200°C) have been established using real time spectroscopic ellipsometry (RTSE) as a probe of film microstructural evolution and optical properties. These deposition phase diagrams describe the regimes over which predominantly amorphous and microcrystalline Si phases are obtained as a function of the accumulated film thickness and the hydrogen-to-silane gas flow ratio, R=[H 2]/[SiH 4]. The diagrams for different substrate materials demonstrate how general principles can be formulated and verified for design of optimized multistep i-layer components of amorphous silicon solar cells.

Deposition conditions and composition and structure relationships for nitride carbon films obtained by ECR plasma-assisted CVD and reactive rf magnetron sputtering

Hydrogenated carbon nitride and carbon nitride films were deposited by ECR plasma-assisted CVD (PACVD) and rf reactive magnetron sputtering. Film composition (N/C ratio), growth rate ( V g) and microhardness H were investigated depending on the type (dc or rf) and the level of substrate bias in the range 0 to −200 V. As was revealed, the ion bombardment influences the composition and growth rate of carbon nitride films during their deposition. An increase in rf bias voltage up to −200 V results in a decrease in V g up to zero, while the dependence of N/C on rf bias value reveals a peak at about −130 to −150 V. Analysis of Raman spectra for both film types indicates a decrease in size of the film-forming clusters and simultaneous arrangement of atoms towards graphite-like structure with increasing ion bombardment intensity. From the resemblance of V g, N/C and Raman spectra behavior to the variation in ion bombardment characteristics, it can be concluded that the ion bombardment effect reveals common features for two essentially different deposition methods, whereas the film growth mechanisms are strongly different for these deposition techniques and substantially influence the composition and growth rate of the films. The microhardness of CN x H y films increased with increasing ion bombardment intensity, but did not exceed 7000 N/mm 2. These effects are related to the film microstructure evolution under the ion bombardment and sp 2 nature of the chemical bonds in the film-forming clusters.

Control of Microstructure and Orientation in Solution‐Deposited BaTiO3 and SrTiO3 Thin Films

Columnar and highly oriented (100) BaTiO3 and SrTiO3 thin films were prepared by a chelate‐type chemical solution deposition (CSD) process by manipulation of film deposition conditions and seeded growth techniques. Randomly oriented columnar films were prepared on platinum‐coated Si substrates by a multilayering process in which nucleation of the perovskite phase was restricted to the substrate or underlying layers by control of layer thickness. The columnar films displayed improvements in dielectric constant and dielectric loss compared to the fine‐grain equiaxed films that typically result from CSD methods. Highly oriented BaTiO3 and SrTiO3 thin films were fabricated on LaAlO3 by a seeded growth process that appeared to follow a standard “two‐step” growth mechanism that has been previously reported. The film transformation process involved the bulk nucleation of BaTiO3 throughout the film, followed by the consumption of this matrix by an epitaxial overgrowth process originating at the seed layer. Both BaTiO3 and PbTiO3 seed layers were effective in promoting the growth of highly oriented (100) BaTiO3 films. Based on the various processing factors that can influence thin film microstructure, the decomposition pathway involving the formation of BaCO3 and TiO2 appeared to dictate thin film microstructural evolution.

TEM studies of the microstructure evolution in plasma treated CVD TiN thin films used as diffusion barriers

In semi-conductor technology, TiN thin films elements are used as diffusion barriers between a copper interconnect layer and a silicon oxide dielectric. Plasma treatment application, by modifying the film microstructure, can improve the film barrier properties and its electrical conductivity. But details of the plasma application effect on the film microstructure evolution and correlations of this evolution with the physical properties are still unclear. To clarify the correlations, the microstructure of a series of TiN thin films deposited using an OMCVD (organo-metallic chemical vapor deposition) technique has been analyzed by transmission electron microscopy (TEM). The films were obtained by cycling a basic synthesis sequence including first a limited film growth and then application of a N 2/H 2 gaseous plasma with various powers and duration times. Films are actually stackings of plasma-treated elementary layers. TEM analyses show that films are made of nanocrystallites and that whereas no texture is observed when no plasma is applied, short-time plasma treatment induces a tendency to 〈100〉 texture and if treatment is longer, the direction of texture progressively rotates to 〈110〉. A tentative interpretation of this texture evolution has been made in terms of nucleation and growth and correlations between this evolution and the effect on the physical properties have been obtained.

Sol-Gel Derived Barium-Strontium Titanate Films

Sol-gel techniques for the preparation of barium-strontium titanate (BST) films are discussed. The evolution of film microstructure during heat treatment, and the dielectric properties of BST films prepared from alkoxide solutions and from alkoxide solutions modified by 2-ethylhexanoic acid were studied. It is shown that the extent of the modification of the precursors by 2-ethylhexanoic acid changes the precursor molecular complexity governing the microstructure of the films and their electrical properties.

The effect of surface transport on the evolution of film microstructure in plasma etching and deposition

Surface transport models proceeding via surface re-emission and surface diffusion are briefly described. The important dimensionless parameter for re-emission is the sticking probability, whereas for surface diffusion, profile evolution is governed by the Damkohler number. The results of our continuum-based models are presented for low pressure deposition. These transport phenomena also occur during etching, and simulation results for the evolution of surface roughness during RIE are presented. Etching of periodic surfaces is considered first. It is shown that for etching, unlike for deposition, surface roughness always decays with time; the greater the sticking probability, the greater the rate of decay. Results for etching of self-affine surfaces are presented. During deposition, it is found that the presence of surface diffusion removes sharp edges from the film profile, especially in the early stages of film growth. During RIE, on the other hand, this “cauliflower” morphology is reduced to sharper asperities, though the “peak-to-peak” roughness decays with time. This microstructure is simulated in patterned features and is particularly important when the characteristic length scale is the same order of magnitude as the critical feature dimension. Experimental results on the evolution of roughness for a PVD process (sputter-deposition of titanium) obtained through AFM are presented, and the growth of rms roughness indicates the relative absence of surface transport.

Grain Rotation and Grain Boundary Selection in Thin Films

ABSTRACTComputer simulations of the phenomenon of grain rotation in polycrystalline <111> textured films have been carried out. These simulations provide insight into the evolution of film microstructure due to grain rotation. It is found that grain rotation diminishes with annealing time and stops almost completely when a metastable equilibrium is obtained. The incidence of Σ1, Σ7 and Σ3 Coincident Site Lattice (CSL) boundaries increases with time while the other CSLs reduce in number. Sequential annealing experiments have been performed on thin films of gold. Grain rotation is found to take place with an average rotation rate of about 4°/hour at both 250°C and 350°C.

Solid-on-Solid Monte Carlo Investigation of Islanding Kinetics During Heteroepitaxy

ABSTRACTWe have investigated the kinetics of islanding during heteroepitaxy using a solid-on-solid Monte Carlo (SOS-MC) simulation. We simulate deposition by randomly depositing atoms onto a square grid with periodic boundary conditions. Arrhenius surface diffusion kinetics are dependent on the sum of a surface energy barrier (Ed) and the number of nearest neighbors multiplied by an adatom interaction strength (Eb). We confine growth to the first layer above the simple cubic substrate and investigate coverages < 1/2 monolayer. We monitor the evolution of film microstructure by producing island size distributions and plots which compare a cluster's area to perimeter ratio with that of a circle. We find that our simulation qualitatively correlates with results of classical film nucleation theory. A simple model is used to demonstrate the existence of a 'probabilistic nucleation barrier'.

Epitaxial growth of PbTiO3 thin films on {100} SrTiO3 from solution precursors

A mixed Pb-Ti-alkoxide liquid precursor, prepared from lead acetate and titanium iso-propoxide was used to form single crystal PbTiO3 thin films epitaxially on {100} SrTiO3 substrates.A gravimetric analysis of the precursor determined its molarity to 0.55 mol/1 and was carried out by drying the alkoxide overnight and heating it to 600° C for one hour. X-ray diffraction showed the resulting PbTiO3 powder to be single phase perovskite. PbTiO3 thin films were formed by spincoating previously annealed (1400°C, 2h) single crystal SrTiO3 substrates. During this process the precursor dries to a gel-like amorphous solid film that pyrolizes and crystallizes to the oxide during heat-treatment. XRD, SEM, TEM and AFM were used to characterize the progress of the epitaxial layer formation as well as the microstructural evolution of films heated at increasing temperatures, ranging from 400°C to 800°C. For XRD Θ-2Θ scans on PbTiO3 thin films heated at temperatures of 450°C and above, only the {00l} tetragonal PbTiO3 reflections (CPTO=0.4153 nm) could be observed, indicating strongly oriented or epitaxial films ({h00} of PbTiO3 (aPTO=0.3899 nm) is masked by (MX)} of the SrTiO3 substrate (aSTO=0.3904 nm)).

Simulation of Y-Ba-Cu-0 Epitaxial Growth and Microstructure Formation

ABSTRACTThe results of systematic computer simulations of the deposition and growth of Y-Ba-Cu-0 thin films is reported. The deposition process is modeled by means of a three-step Monte Carlo simulation incorporating one sorption deposition mode and two modes of film annealing addressing surface and bulk diffusion. The simulation is used to investigate the evolution of surface morphology and film microstructure, growth rate anisotropy, and the dependence of film texture on deposition parameters. Characteristic defects and surface morphologies observed by simulation are found to be in good agreement with those observed experimentally. It is observed that surface kinetics can dominate the evolution of film microstructure.

Development and evolution of thin film microstructures: A Monte Carlo approach

A computer simulation procedure based on the Monte Carlo algorithm has been developed to study the thin film microstructure evolution in the Zone II regime. This is accomplished by letting the grain boundary movement on the film surface couple with the microstructure in the interior of the film. The grains when viewed in cross-section are found to reach a limiting size at which point all grain boundary motion ceases despite the presence of capillarity driving force. This results in a columnar morphology for the thin film. The cross-sectional size distribution function is found to be approximately log-normal in shape. The introduction of anisotropic solid-vapor interfacial energy is found to induce abnormal grain growth at the expense of the normal grain which has a relatively higher solid-vapor energy. An analytical model is proposed in which the formation of the columnar structure is explained in terms of the grain boundary drag at the growing interface due to sub-surface boundaries.

The role of ion/surface interactions and photo-induced reactions during film growth from the vapor phase

Recent progress in the understanding of mechanisms associated with low-energy (often < 100 eV) ion/surface interactions and photo-induced reactions during vapor-phase crystal growth are reviewed. Ion/surface interactions play an important role in a variety of deposition technologies including sputtering, plasma-assisted chemical vapor deposition, and, more recently, molecular beam epitaxy. Effects such as trapping, preferential sputtering, and collisional mixing are used to interpret and, in some cases, model experimental results concerning the effects of low-energy ion bombardment on nucleation and film growth kinetics, the evolution of film microstructure, elemental incorporation probabilities, surface segregation rates, and dopant depth distributions. The role of photo-stimulated gas-phase and surface reactions during laser-assisted chemical vapor deposition, including single, multiple, and multiphoton-initiated processes, radical production, and adlayer photochemistry, are also discussed together with newly developed laser-processing techniques during deposition. The focus of this review is on the development of an understanding of the controlling mechanisms in both ion/surface and photo-stimulated processes.