Formation Process Of Thin Films Research Articles

A Monte Carlo Simulation on the Process of Cluster Deposition

Cluster deposition process is expected to open a new scheme for thin-film formation process, which realizes better physico-chemical properties than by conventional processes. We simulate the variants of morphologies of thin films fabricated by the cluster deposition, since it is important to investigate the properties of the thin film. In this paper, a Monte Carlo method is applied to describe the motion of clusters and monomers. The present numerical simulation is performed on a three-dimensional lattice. Some growth morphologies are obtained, and the relationship between the resultant morphologies and the parameters used in the simulation such as deposition rate and size of the clusters are examined.

The Fate of a Cluster Colliding onto a Substrate Dissipation of Translational Kinetic Energy

The fate of clusters emitted onto a substrate falls into several categories including repulsion, soft landing, migration, and explosion, depending on the interaction between the cluster and the substrate. This dynamic behavior of the clusters controls thin-film formation processes from clusters such as cluster ion beam deposition and chemical vapor deposition. Here we describe the collision processes of both Al and Au clusters with a kinetic energy of ∼0.56 eV/atom onto an amorphous SiO2 substrate studied by molecular dynamics simulation, focusing on the dissipation of translational kinetic energy during the collision process. The simulation elucidated that the activation of thermal vibrational energy of the substrate promoted the sticking of the colliding clusters on the substrate. This result suggests that the dissipation of the translational kinetic energy of the colliding cluster is one of the factors that determine the structure formed on a substrate from vapor phase.

Thin film formation processes controlled by the momentum parallel to the substrate surface

Surface electronic structures of adsorbed nitrogen atoms on the oxidized nickel substrate were investigated by angle-resolved transmission current spectroscopy in a magnetic field. The density distributions of d I t( k θ, k r )/d B and d I t( k θ, k r )/d V in a two-dimensional wave number vector ( k θ, k r )-space strongly depended on the gas pressure. The surface structure changed from the disordered layer with the superlattice structure of (110) surface of NiO to the stepped structure due to adsorbed nitrogen atoms on the superlattice. The angle of the stepped structure increased with increasing pressure. The ionization process showed the same angle dependence as that of the adsorbed nitrogen atoms, but the magnitude of the wave number vectors were different from each other because of the binding energy. These results suggested two adsorbed layers on the surface oxide. The shift of the wave number vectors to the direction parallel to the surface with the increase of pressure showed the importance of the momentum parallel to the surface.

Formation Process and Electrical Property of RuO2 Thin Films Prepared by Reactive Sputtering

Ir and IrO2 thin films were prepared by reactive sputtering in Ar+O2 gas. The formation process of Ir and IrO2 films was classified into three regions depending on the O2 flow ratio; (a) metal region, (b) high deposition rate oxide region, and (c) low deposition rate oxide region. Supplied O2 molecules in region (a) were gettered by Ir atoms sputtered on the chamber wall and O2 partial pressure was very low. In region (b), since the amount of supplied O2 molecules exceeds the total amount of sputtered Ir atoms, IrO2 films are formed at the substrate surface. In region (c) the surface of the Ir target is thought to be oxidized and the deposition rate of IrO2 film decreases. Resistivity of the IrO2 films decreases with an increase of substrate temperature and the minimum resistivity of 83 µΩcm is obtained at 400°C. However, mixture-phase films of Ir and IrO2 were formed at 500°C.

ＴＧ‐ＭＳによるセラミック薄膜および粉体の形成過程の解明

ＴＧ‐ＭＳによるセラミック薄膜および粉体の形成過程の解明

Ion energy, ion flux, and ion species effects on crystallographic and electrical properties of sputter-deposited Ta thin films

The effects of ion bombardment conditions on the crystallographic and electrical properties of tantalum thin films grown on SiO2 and Si have been systematically investigated in Ta thin film formation process employing low-energy (<100 eV) inert-gas ion bombardment on a growing film surface. It is demonstrated that the properties of Ta films are strongly dependent upon ion energy and ion flux as well as substrate materials. The bcc-Ta can be formed on SiO2 by controlling impinging ion energy and normalized ion flux defined as the ratio of ion flux to Ta flux ranging lower than 20 eV and higher than 13, respectively, for Ar plasma. Based on these results, low-resistivity bcc-Ta thin films (14.8 μΩ cm at 300 K) have been successfully formed. It is also experimentally shown that the irradiation by ions with different mass numbers has different effects on growing film properties, even if the energy or momentum of the ions is the same. When normalized ion flux is 26, bcc-Ta films can be grown on Si at ion energy lower than 30 eV for Ar ions and at ion energy ranging from 30 to 90 eV for Xe ions. The results also suggest that there are two cases where the phase transition from bcc to β occurs. One is caused by defects induced by the recoil implantation of Ta atoms due to the excessive higher-energy ion bombardment and the other is induced by defects due to insufficient total energy input to a growing film surface by ion irradiation and resulting poor film quality.

薄膜形成プロセスのコンピューターシミュレーション法

薄膜形成プロセスのコンピューターシミュレーション法

A Molecular Dynamics Simulation on Thin Film Formation Process of Surfactant-Mediated Growth

AbstractThe phenomenon of surfactant-mediated growth has been successfully simulated by means of a molecular dynamics method using two-dimensional model atoms interacting via a Lennard-Jones potential. Surfactant atoms were placed on a substrate, and then film atoms were deposited. Under adequate experimental conditions, the surfactant atoms could stay at the growing surface by exchanging their positions with the deposited atoms. Effects of various conditions on the morphology of the film surface were precisely investigated by the simulations.

ＬＰＤ法による金属基材へのＳｉＯ２薄膜の作製

By using LPD (Liquid Phase Deposition) method, SiO2 thin film can be formed in H2SiF6 aqueous solution below 50°C. However, in almost all cases, thin films formed by LPD method were on glass substrate. Therefore, in this study, problems concerning the SiO2 film formation process on SUS304 stainless steel substrate were examined by incorporating various electrochemical techniques. From the results of potential and current density measurements under coupling conditions with a Pt counter electrode, the importance of keeping SiO2 supersaturated state of solution and the need of pretreatment and cathodic protection of stainless steel substrate were recognized for preventing the corrosion damage of substrate from the severe environment of H2SiF6 aqueous solution.Then, the thin SiO2 film formation process was examined through microscopic observations by SEM and chemical analysis by EPMA. As a result, the progress in the deposition process was recognized with time. However, some defects were recognized in the deposited thin SiO2 film on SUS304 stainless steel substrate. These defects may strongly influence the corrosion resistance of SiO2 thin film coated steel. On the other hand, some acceleration in the thin film formation process was recognized when the deposition was conducted under a cathodically protecting condition at which an aluminum piece was used as a sacrificial anode. It may be brought about by the acceleration in anodic dissolution of aluminun piece and also by the pH increase with H2 gas generation in the electrochemical reaction.

Effect of Zr/Ti Ratio on Crystal Structure of Thin Lead Zirconate-Titanate Films Prepared by Reactive Sputtering

Thin lead zirconate-titanate (PZT) films have been synthesized on MgO(100) using the tripole magnetron sputtering system. This system makes it possible to sputter lead and zirconium-titanium alternately. Lead concentration in the deposited films can be easily adjusted to near stoichiometry through the control of substrate temperature. The c-axis-oriented films with perovskite structure of Morphotropic Phase Boundary composition were obtained at 550°C via the self-limiting process of lead concentration. The formation process of thin PZT films has been investigated with reference to the observed results of the dependence of the crystal structure on Zr/Ti ratio as well as lead concentration in the films.

Molecular dynamics modeling of microstructure and stresses in sputter-deposited thin films

A molecular dynamics model to study thin film formation processes is presented. In this model, the Lennard-Jones and Moliére potential functions are used to describe the interaction between the atoms, and ions and atoms, respectively, and determine the atomic forces among the atoms. A third-order, nonuniform time step integration scheme is used to determine the new position and velocity of each particle within the film and the substrate. The use of nonuniform time interval results in significant savings in CPU time. The force evaluation is performed in a short cutoff range which requires that the list of neighbor particles be known. A ‘‘position index method’’ which is much more efficient than the previous schemes, is proposed and implemented in order to sort the table of atoms locally. The frictional force originating from the heat bath is represented by using the generalized Langevin equation such that the temperature of the substrate can be kept constant during the film growth. A moveable periodic boundary condition which can allow the film to expand or contract depending on the internal stresses within the film and the substrate, is used in the present molecular dynamics (MD) model. A local stress parameter is defined in order to examine the effects of defects, voids, and gas impurity on local stress distribution. The intrinsic stresses are then calculated from the film structure. This improved MD model can predict the effect of adatom energy, ion bombardment, and gas impurity on microstructure and intrinsic stresses in thin films very successfully.

Aggregation at Early Stage of Growth in Thin Films

A growth model is presented to simulate the diffusion-limited aggregation pattern appearing in the formation process of thin films deposited by sputtering or evaporation. In the submonolayer range of deposits, aggregates are controlled by the sticking probability of sputtered (or vaporing) particles, the ballistic motion of particles and Brownian motion of particles on the deposition plate. By using computer simulation it is found that the deposit at early stage of growth becomes a quasi-two dimensional structure extending on the deposition plate at a typical height of a few particles. The pattern obtained by the computer simulation is similar to that found in experiments. A top view of the structure of clusters deposited on the plate shows the DLA fractal at low particle numbers. The cluster-size distribution n s ( t ) obeys the dynamic scaling: n s ( t )≈ t w s -τ f ( s / t z ) (τ=0.92±0.03, z =0.34±0.01, and w =0.58±0.03) where the cutoff function f ( x ) is a constant for x ≪1. The scaling structure o...

Formation Process of SnO<sub>2</sub> Thin Films by Sol-Gel Method

Tin Oxide thin films were prepared by sol-gel method using colloidal particles derived from an inorganic salt. The thickness (t) of SnO2 films and the pulling rates (v) of substrates from dipping solutions were correlated with an expression of t∝v0.53. The formation process of SnO2 thin films was studied. Well-crystallized SnO2 thin films were obtained above 550°C after successive dehydration of OH groups. SnO2 thin films prepared at 550°C were composed of very fine particles with 10-20nm in diameter. Firing at higher temperatures caused the grain growth without substantial densification of the films, leading to coarse microstructure.

薄膜形成過程の計算機シミュレーション

薄膜形成過程の計算機シミュレーション

Molecular Dynamics Study of the Thin Film Formation Process

Abstract The initial stage of thin film formation process was studied by the molecular dynamics method. The Morse function was assumed as the interaction potential between the substrate-substrate, substrate-deposited and deposited-deposited atoms. The interfacial structure of the calculated system was restricted to be coherent, i.e. the structures of the substrate and the deposited atoms were both fcc and had the same lattice constants. The depth of the potentials for the three types of interaction was changed to study its effects on the film structure. The substrate temperature was also varied to see the temperature dependence of the relaxation process of the film structure. Two kinds of structure of the deposited films were considered; three atomic layers of fcc(111) and a monolayer of fcc(111). Both consisted of 19 atoms. They were considered as the nucleus of the film at the initial stage of the deposition process. The deposited nuclei were relaxed into equilibrium shapes such as the monolayer, the 3 ...

New approach for a computer simulation of the vacuum deposition process

Computer simulations were made of the formation process of vacuum-deposited thin films by the use of a hybrid method in which a deterministic algorithm and a stochastic algorithm were combined. The traces of the film atoms were calculated by molecular dynamics, while those of the substrate atoms were generated from a modified Langevin equation. It was found that the rapid structural relaxation of the deposited film assisted by the thermal energy of the substrate and that of the incident beam was needed for the occurrence of the layered structure of thin films with high crystallinity. The dependences of the film growth on the energy parameters of the atomic interaction, the deposition rate, and the substrate temperature were studied in detail.

キャンペーン特集 コンピュータシミュレーションの世界 計算機シミュレーションによる薄膜形成過程の研究

キャンペーン特集 コンピュータシミュレーションの世界 計算機シミュレーションによる薄膜形成過程の研究

Computer experiments of initial growth kinetics of vacuum-deposited thin films

The formation process of thin films is studied by the Monte Carlo method. The reason for the occurrence of the three different growth modes i.e. the Volmer-Weber mode, the Frank-van der Merwe mode and the Stranski-Krastanov mode is discussed in relation to the parameters used in the Morse potential. It is suggested that the growth mode is mainly determined by the energy parameters rather than the experimental conditions of the film growth except for the Stranski-Krastanov mode.

Computer Simulation Study of Thin Film Formation Process

AbstractThe thin film formation process was studied by the molecular dynamics(MD) method and by the hybrid method which combined the MD method with the Monte Carlo(MC) simulation technique. The Morse potential was assumed as the atomic interaction model. The substrate temperature was changed to see its effect on the film structure. The MD simulation found that the reconstruction process of the deposited nuclei was essential to determine the metastable film structure and that the relaxed atomic arrangements were strongly dependent on the depth of the interaction potentials. The hybrid method simulated the high rate deposition process and confirmed the results of the MD simulation.

Atomic structure in SiO2 thin films deposited by remote plasma-enhanced chemical vapor deposition

We have studied selected structure-dependent properties of thin films of SiO2 prepared by remote plasma-enhanced chemical vapor deposition (remote PECVD) and thermal oxidation of crystalline silicon, and have identified process-dependent differences in their local atomic structures. We have determined the frequency ν and linewidth Δν of the Si–O bond-stretching infrared-active vibration near 1075 cm−1, and have found that all relatively thick oxide films, t>1000 Å, prepared by either of these two techniques display the same linear relationship between Δν and ν. This behavior has been interpreted in terms of a central force model that gives the average bond angle 2θ at the oxygen atom sites, and attributes the linewidth to a distribution of vibration modes associated with a ±30° spread in 2θ. We have determined that (i) in remote PECVD films deposited at temperatures (Ts ) between 200 and 350 °C, 2θ varies between 140° and 144°; (ii) in thermal oxides grown over a temperature range (Tox ) between 800 and 1150 °C, 2θ varies from about 147° to 150°; and (iii) in thick oxide films, independent of the preparation method, Δθ/θ is equal to 0.21±0.01. We have compared other oxide properties as well: (a) the optical index of refraction n at 632.8 nm, (b) the intrinsic stress σi, and (c) the etch rate in buffered HF (6:1). In addition, we discuss the electronic properties of remote PECVD and thermally grown SiO2 films in metal–oxide–semiconductor (MOS) structures, where we have observed that the same device quality MOS properties can be obtained in structures employing both types of oxide films. Finally, we compare stress and strain in the remote PECVD and thermal oxides in the immediate vicinity of the Si/SiO2 interface, and the bulk of the oxide films, and correlate the differences we observe with fundamental differences in the two thin-film formation processes.