Growing Film Surface Research Articles

Effects of substrate bias voltage on the microstructure, mechanical properties and tribological behavior of reactive sputtered niobium carbide films

Niobium carbide films have been deposited on Si(100) substrates using direct current reactive magnetron sputtering in discharging a mixture of CH4 and Ar gas. The effects of substrate bias voltage (Vb) and methane flow rate (FCH4) on the phase structure, composition, morphology, mechanical properties and tribological behavior for NbC films have been explored. For the film grown at FCH4=6sccm, a phase transition from a mixture of hexagonal-Nb2C and cubic-NbC phases to cubic-NbC phase occurs with increasing the absolute value of Vb and no CC bonding appears. In contrast, for the film deposited at FCH4=16sccm, only the cubic-NbC phase is observed with increasing the absolute value of Vb and the CC bonding appears. If FCH4 is fixed at either 6 or 16sccm, as the absolute value of Vb is increased, the growing film surface becomes smoother, and the compressive stress increases. This can be attributed to the increase in the carbon ion bombarding energy, which leads to promoting the diffusion of adsorbed atoms and more carbon species' occupying the interstitial positions. It is found that the hardness (H) increases first, and then decreases after reaching a maximum value with increasing the absolute value of Vb. The friction coefficient for the film obtained at FCH4=16sccm is lower than that at FCH4=6sccm, which may be ascribed to the presence of either graphite or amorphous carbon in the film grown at FCH4=16sccm. Furthermore, a high stress results in a poor wear resistance.

Phase transformation of diamond-like carbon/silver composite films by sputtering deposition

This study fabricated hydrogenated diamond-like carbon/silver bioceramic films on glass substrates using radio frequency magnetron sputtering with a single silver target in an atmosphere of Ar/CH4 mixture. The effects of applied power on the composition and microstructure of bioceramic film were evaluated. A phase transformation, amorphous diamond-like carbon → nano-silver precipitation → nano-silver growth in the amorphous diamond-like carbon matrix was observed during sputtering. The film growth rate, surface roughness, silver content and size of silver nanoclusters in the films all increased with the silver target power due to the higher flux of sputtered silver species toward the substrate.

Sputtering characteristics, crystal structures, and transparent conductive properties of TiOxNy films deposited on α-Al2O3(0 0 0 1) and glass substrates

Adding N2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO1−xNx having a face-centered cubic (fcc) structure to TiO2−xNx having an anatase structure. Titanium oxynitride films deposited on an Al2O3(0001) substrate were epitaxial with major orientations toward the (111) and (200) directions for fcc-TiO1−xNx and (112) for anatase-TiO2−xNx. Intermediately oxidized films between TiO1−xNx and TiO2−xNx were amorphous on the glass substrate but crystallized into a Magneli phase, TinO(N)2n−1, on the Al2O3(0001) substrate. Partially substituting oxygen in TiO2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO2−xNx films on Al2O3(0001) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiOxNy films vary continuously with changing N2 flow rate, their transparent conductive properties can be controlled more easily than TiOx. Nb5+ ions could be doped as donors in TiO2−xNx anatase crystals.

Tilting of carbon encapsulated metallic nanocolumns in carbon-nickel nanocomposite films by ion beam assisted deposition

The influence of assisting low-energy (∼50-100 eV) ion irradiation effects on the morphology of C:Ni (∼15 at. %) nanocomposite films during ion beam assisted deposition (IBAD) is investigated. It is shown that IBAD promotes the columnar growth of carbon encapsulated metallic nanoparticles. The momentum transfer from assisting ions results in tilting of the columns in relation to the growing film surface. Complex secondary structures are obtained, in which a significant part of the columns grows under local epitaxy via the junction of sequentially deposited thin film fractions. The influence of such anisotropic film morphology on the optical properties is highlighted.

Kinetics of formation and growth of epitaxial SrTiO3 films of single-crystal (001) SrTiO3 supports

The aim of this study was to quantitatively estimate the kinetics of the formation and growth of oxide SrTiO3 (STO) films using the method of the in situ reflection high-energy electron diffraction (RHEED) and compare the obtained results with the known growth models and theoretical estimates. The kinetics of the relaxation and crystallization of particles is studied under pulsed laser deposition (PLD) from oxide targets onto (001) STO supports or onto the surface of STO film growth at 650–800°C. Deposition frequencies of 0.1–10 Hz typical of PLD were used. The surface morphology and film structure was studied ex situ using the methods of AFM and X-ray-structural analysis. It was found that the time of relaxation of deposited particles is within the range of 2–20 s, which greatly exceeds or is comparable to the relative pulse duration. It was experimentally shown that structural distortions in epitaxial films for temperatures of ≤900°C are mainly due to the high rate of deposition and limited surface mobility of particles. The effect of structural relaxation in films is observed after the end of deposition; the time constant of bulk structural relaxation is ∼10 − ∼102 s or more. The obtained kinetic parameters of the formation of an oxide structure may be useful for the development of crystallization theory, as well as to optimize the conditions of epitaxial oxide film growth.

Sputter joining of TiO2 / SiO2 thin film system

Attempt has been made to join TiO2 / SiO2 multilayer thin films at low temperature during sputter deposition. Joining strength was evaluated by haze value after abrasion test. Joining strength was found to be improved by forming Al2O3 layer of 10 nm thickness at the interface between TiO2 and SiO2. Transmission electron microscopic observation revealed the formation of disordered layer at the interfaces of SiO2 / Al2O3 and Al2O3 / TiO2. Results can be explained in terms of the formation of disordered interfacial structures without special heat treatment caused by local heat evolution at growing film surface by the deposition of kinetic energy of sputtered particles.

Chemical Activity of Oxygen Atoms in the Magnetron Sputter-Deposited ZnO Films During Film Growth

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied in a deposition and post-deposition study in which the deposition of a several-nanometer-thick ZnO layer altered with an exposure to an O2/Ar mixed plasma, i.e., a layer-by-layer (LbL) technique. The film crystallization was promoted by suppressing the oxygen vacancy and interstitial defects by adjusting the exposure conditions of the O2/Ar plasma. These findings suggest that the chemical potential of the oxygen atom influences the film crystallization and the electronic state. The diffusion and effusion of oxygen atoms at the growing surface have an effect similar to that of thermal annealing, promoted film crystallization and the creation and the annihilation of oxygen- and zinc-related defects. The role of oxygen atoms reaching the growing film surface is discussed in terms of chemical annealing and a possible oxygen diffusion mechanism is proposed.

Chemical Activity of Oxygen Atoms in Magnetron Sputter-Deposited ZnO Films during Film Growth

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and an O2/Ar mixed plasma exposure, i.e., a layer-by-layer (LbL) technique. Film crystallization was promoted by suppressing the formation of oxygen vacancies and interstitial defects by adjusting the exposure conditions of the O2/Ar plasma. These findings suggest that the chemical potential of oxygen atoms influences film crystallization and the electronic state. The diffusion and effusion of oxygen atoms at the growing surface have effects similar to those of thermal annealing, namely, the promotion of film crystallization and the creation and annihilation of oxygen- and zinc-related defects. The role of oxygen atoms reaching the growing film surface is discussed in terms of chemical annealing, and a possible oxygen diffusion mechanism is proposed.

Chemical Activity of Oxygen Atoms in Magnetron Sputter-Deposited ZnO Films during Film Growth

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and an O2/Ar mixed plasma exposure, i.e., a layer-by-layer (LbL) technique. Film crystallization was promoted by suppressing the formation of oxygen vacancies and interstitial defects by adjusting the exposure conditions of the O2/Ar plasma. These findings suggest that the chemical potential of oxygen atoms influences film crystallization and the electronic state. The diffusion and effusion of oxygen atoms at the growing surface have effects similar to those of thermal annealing, namely, the promotion of film crystallization and the creation and annihilation of oxygen- and zinc-related defects. The role of oxygen atoms reaching the growing film surface is discussed in terms of chemical annealing, and a possible oxygen diffusion mechanism is proposed.

Macroscopic Approach to Plasma Polymerization Using the Concept of Energy Density

AbstractThe film growth and the properties of plasma polymers are determined by gas phase and surface reactions. In order to gain more insights and to optimize plasma polymerization processes, some assumptions can be made that allow a macroscopic approach. Therefore, a concept was developed based on the energy input both into the gas phase (plasma) and during film growth (surface) that helps to distinguish between predominating gas phase or surface processes. Different experimental series using gas mixtures of C2H4 with CO2 or N2/H2 were performed at different power inputs W and gas flow rates F. Thereby, the same range of specific energy input W/F can be maintained at different ion bombardment to the substrate. The results indicate that changes in film growth were initiated by plasma chemical processes for CO2/C2H4 discharges (scavenger effects), while the obtained drop in deposition rate at high energy input values for N2/H2/C2H4 is caused by the energy dissipated in the film during growth pointing towards a threshold energy for chemical sputtering.magnified image

Room-Temperature Formation of Low Refractive Index Silicon Oxide Films Using Atmospheric-Pressure Plasma

This study aims to apply atmospheric-pressure (AP) plasma to the fabrication of single-layer anti-reflection (AR) coatings with porous silicon oxide. 150 MHz very high-frequency (VHF) excitation of AP plasma permits to enhance the chemical reactions both in the gas phase and on the film-growing surface, increasing deposition rate significantly. Silicon oxide films were prepared from silane (SiH4) and carbon dioxide (CO2) dual sources diluted with helium. The microstructure and refractive index of the films were studied using infrared absorption and ellipsometry as a function of VHF power density. It was shown that significant increase in deposition rate at room temperature prevented the formation of a dense SiO2 network, decreasing refractive index of the resulting film effectively. As a result, a porous silicon oxide film, which had the lowest refractive index of 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave AR coating of a glass plate.

Influence of gas phase and surface reactions on plasma polymerization

The formation of plasma polymers is based on multistep reactions that are taking place both in the gas phase and on the surface of the growing film. In order to gain more insights and to control plasma polymerization processes, some assumptions can be made that allow a macroscopic description. Following this idea, a concept was developed based on the energy input both into the gas phase (plasma) and during film growth (surface) that helps in up-scaling plasma polymerization processes. In order to test this concept, various a-C:H:N thin films were deposited under different NH3/C2H4 gas ratios, power inputs W, and gas flow rates F. Thereby, the energy consumed in the gas phase is controlled by W/F yielding a flux of film-forming species. The comparison of two comparable plasma reactors of different sizes indicate that while the reaction parameter W/F plays a major role for the transfer of plasma polymerization processes, the energy input into the film by ion bombardment during film growth should also be taken into account.

Study of the Reflectivity of Silver Films Deposited by Radio Frequency and Direct Current Coupled Magnetron Sputtering

Silver films are deposited on a SiO2 surface and a cyclo-olefin polymer surface by radio frequency and direct current (RF–DC) coupled magnetron sputtering to realize light reflectors with high reflectivity in the visible light region. Because the reflectivity of silver is relatively low, especially in the short-wavelength region less than 500 nm owing to a slight increase in the refractive index of silver, deposition conditions are studied with emphasis on maximizing the reflectivity in this region. Also, protection film depositions of Si3N4 on a silver surface by microwave-excited-plasma-enhanced chemical vapor deposition were carried out to improve the durability of silver films, which are easily oxidized and/or sulfurized, resulting in the degradation of the reflectivity of the films. It is found that a high reflectivity in the short-wavelength region can be obtained by Xe plasma sputtering and/or Ar plasma sputtering at a relatively high working pressure, i.e., the conditions with a low ion bombardment energy at the substrate surface. At the same time, a normalized ion flux supplied to the substrate surface at approximately 2 is optimum, where the normalized ion flux is defined as the ratio of plasma-ion flux to deposited-atom flux on the growing film surface. Under such optimized deposition conditions, a silver film with a low resistivity and a smooth surface is obtained. Furthermore, it is found that a Si3N4 film with a thickness of 8 nm on a silver surface serves as a good protection film without serious degradation of reflectivity, and the reflectivity can be maintained even after the immersion of the sample in the boiling water (100 °C) for 2 h.

Growth kinetics of plasma deposited microcrystalline silicon thin films

A continuum model for the nucleation and growth of microcrystalline silicon thin films from SiH4/H2 discharges is presented. The simulation considers mass balances and surface coverage with adspecies and silicon clusters up to the size where they can be considered as thermodynamically stable. The model is combined to a plasma gas phase simulator and a simulator of thin film morphology and is used for studying the growth differences in two different regions, the center and the edge of a 30×30cm2 substrate. The predictions for the film growth rate, film crystallinity and surface roughness in both regions are presented and discussed together with the main processes governing nucleation and growth and the slow step for stable nanocrystal formation.

Chemical activity of oxygen atoms in the magnetron sputter-deposited ZnO films

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and an O 2/Ar mixed plasma exposure, i.e., a layer-by-layer (LbL) technique. The film crystallization was promoted by suppressing the oxygen vacancy and interstitial defects by adjusting the exposure conditions of the O 2/Ar plasma. These findings suggest that the chemical potential of the oxygen atom influences the film crystallization and the electronic state. The diffusion and effusion of oxygen atoms at the growing surface have an effect similar to that of thermal annealing, promoted film crystallization and the creation and the annihilation of oxygen- and zinc-related defects. The role of oxygen atoms reaching at the growing film surface is discussed in terms of chemical annealing and a possible oxygen diffusion mechanism is proposed.

Nanocrystalline Silicon Films Grown at High Pressure in Very High Frequency Plasma Enhanced Chemical Vapor Deposition System

Nanocrystalline silicon films have been fabricated from SiH4 diluted with H2 in very high frequency (40.68 MHz) plasma enhanced chemical vapor deposition system at low temperatures (250oC). The influence of pressure on the structural properties of nanocrystalline silicon films has been investigated. The experimental results reveal that a very high hydrogen dilution is needed to crystallize the film grown at high pressure. If the hydrogen dilution is not high enough, the film could also be crystallized through lowering the pressure. Furthermore, the crystallinity and grain size increase with decreasing the pressure. These results could be attributed to the increase of ion bombardment energy and the higher atomic hydrogen flux toward the growing film surface at lower pressures.

ChemInform Abstract: Formation of Copper Thin Films by a Low Kinetic Energy Particle Process.

This paper reports on low kinetic energy particle bombardment of a growing film surface employed to grow high-quality copper thin films on silicon and SiO{sub 2} with ideal metal/substrate interface characteristics. It is shown that the energy of Ar ions concurrently bombarding a growing film surface determines the crystal structure of the film. Under relatively low-energy ion bombardment conditions (100)- or (111)-oriented films are obtained either on (100)Si (111)Si, or SiO{sub 2} surfaces when large ion bombardment energies are employed. It has been found that (111)-oriented films thus created on SiO{sub 2} are metastable and easily transform by thermal annealing into completely (100)-oriented films with large grains of about 100 {mu}m. This unique transformation phenomenon has been successfully applied to the formation of almost single-crystal (100)-oriented Cu islands on SiO{sub 2}. In situ substrate surface cleaning by extremely low energy Ar ion bombardment has enabled the formation of ideal metal/silicon contacts without any postmetallization alloying heat cycles. Excellent adhesion of Cu thin films on SiO{sub 2} has also been demonstrated by the employment of the in situ substrate surface cleaning.

RF power density dependent phase formation in hydrogenated silicon films

Hydrogenated amorphous and micro/nanocrystalline silicon films have been deposited using RF (13.56 MHz) PECVD technique in the RF power density range of 177 to 885 mW/cm 2 exploiting SiH 4 + H 2 + Ar gaseous mixture. Predominant crystalline phase was observed in the films, as revealed from Raman spectroscopic study, deposited at power densities of 531 and 708 mW/cm 2 and amorphous phase at 177, 354 and 885 mW/cm 2. Amorphous to microcrystalline phase transition occurred near RF power density of 531 mW/cm 2. The high crystalline phase (~ 80%) was found in the film deposited at 708 mW/cm 2. Lower values of bond angle distortion of 6.7 and 5° were found for the films deposited at 531 and 708 mW/cm 2 as compared to bond angle distortion of 8.4, 9.3 and 9.1° for the films deposited at 177, 354 and 885 mW/cm 2, respectively. Plasma parameters extracted from V/I probe and properties of the films revealed contribution of ions to be beneficial for the enhancement of deposition rate of the films. The increased ion energy (sheath field) and ion flux together with SiH x (x = 1,2,3) radicals on growing film surface might help in the enhancement of crystallinity at 708 mW/cm 2.

Role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and the O2/Ar mixture plasma exposure, i.e., layer-by-layer technique. The film crystallization promoted with suppressing the oxygen vacancy and interstitial defects by adjusting the exposure condition of O2/Ar plasma. These findings suggest that the chemical potential of oxygen atom determine the film crystallization as well as the electronic state. The diffusion and effusion of oxygen atoms at the growing surface play a role of thermal annealing, promoted the film crystallization as well as the creation and the annihilation of oxygen and zinc related defects. The role of oxygen atoms reaching at the film-growing surface is discussed in term of chemical annealing. The possible oxygen diffusion mechanism is proposed.

Photoinduced Phase Transformations in Boron Nitride: New Polytypic Forms of sp3-Bonded (6H- and 30H-) BN

New sp3-bonded polytypic forms of boron nitride (BN), namely, 6H-BN and 30H-BN, were prepared by plasma-assisted chemical vapor deposition (CVD) with an excimer laser at 193 nm being irradiated on the growing film surface. Only the 6H-BN was formed by postdeposition laser irradiation (PDL) of sp2-bonded BN precursor films prepared by plain plasma-assisted CVD. The PDL demonstrated direct photoinduced phase transformation from sp2-bonded BN into denser sp3-bonded BN here. Typical lattice constants a and c for 6H-BN determined by X-ray diffraction were 2.501 A and 12.45 A, respectively, while those for 30H-BN were 2.538 A and 62.61 A, respectively. The polytypic structures were analyzed in terms of “hexagonality” H and “close-packing” index D, and the “metastability” ΔE estimated by the first principles calculations. Linear relationships were found among the H, D, and ΔE for the polytypes of BN, AlN, and SiC, whose behavior proved to depend on the degree of ionicity in their iono-covalent bonds. The growth ...