On the epitaxy of aluminum nitride on silicon substrates in a chloride-hydride process

The technological conditions under which the silicon surface interacts with vapor-phase reactants present in a chloride-hydride system for the epitaxial growth of aluminum nitride are determined. The method of electron channeling patterns is used to show that the growth of single-crystal layers of AlN on silicon substrates in the chloride-hydride system is hindered by the interaction of the silicon with NH₃ in the presence of HCl at T⩽800°C, with the formation of an amorphous layer of Si₃N₄. To obtain a high-quality texture it is important that prior to deposition of the AlN layers the silicon substrates be held in an NH₃ atmosphere in order to form a dense layer of Si₃N₄. Single-crystal growth of AlN can be achieved in a chloride-hydride system of chemical deposition from the vapor phase at a reduced pressure, since the deposition temperature is then substantially lower (down to 550°C) and the chemical interaction with the substrate is hindered. Pis’ma Zh. Tekh. Fiz. 24, 52–57 (October 26, 1998)     

High rate deposition of hafnium nitride by activated reactive evaporation (ARE)

Cemented carbide inserts are being successfully coated with HfN using the chemical vapor deposition process. Their machining performance is much better than that of uncoated tools. To coat high speed steels with HfN at low deposition temperatures and high rates, we have to resort to physical vapor deposition processes. This paper is concerned with the synthesis of HfN by the activated reactive evaporation (ARE) process and characterization of the deposits. Hafnium was evaporated from an electron beam source in the presence of the reactive gas, nitrogen, the vapor species being activated in the ARE process. The evaporation rate of the metal, reactive gas pressure, deposition temperature and the substrate material were the experimental variables. On stainless steel and high speed steel substrates HfN could be deposited, whereas on tantalum substrates, only mixtures of hafnium, Hf₃N₂, Hf₄N₃ and HfN could be deposited. The microhardness of the deposits varied from 1850 to 2420 KHN.     

Deposition of conductive materials on textile and polymeric flexible substrates

This paper describes the study, analysis and selection of textile and similar materials to be used as flexible substrates for thin conductive film deposition, in the context of integrating electronics into textiles. Kapton^® polyimide was chosen as reference substrate material, was characterized regarding mechanical and electrical properties and was used as a basis for a comparison with several textile substrates. Samples were fabricated using physical vapour deposition (thermal evaporation) to deposit a thin layer of aluminium on top of Kapton and textile substrates. The measurement of electrical resistance of the thin aluminum films was carried out using the Kelvin method. To characterize the mechanical behaviour of the substrate and aluminum film, several mechanical tests were performed and results were compared between Kapton and these textile materials. The chemical composition of the textile substrates and aluminum films as well as the continuity of the films was characterized. This selection process identified the material that was closer to the behaviour of polyimide, a flexible, but non-elastic woven textile coated on both sides with PVC.     

Vapor growth of thin heteroepitaxial InP films on CdS

InP was heteroepitaxially deposited onto CdS single-crystal substrates by chemical vapor deposition using phosphine (PH₃), HCl and indium as reactants. Single-crystalline films were deposited at substrate temperatures as low as 450°C. Scanning Auger microscopy shows that the films are InP and that formation of solid solutions between the CdS and the InP is minimal. The as-grown films are n type with residual donor densities of 4 × 10¹⁶–4 × 10¹⁷ cm^-3.     

Diamond deposition on cemented carbide by chemical vapour deposition using a tantalum filament

Diamond deposition on WC-Co cemented carbide was examined by chemical vapour deposition using a tantalum filament. The filament was much superior to conventional tungsten filament for high-temperature use. Diamond film was deposited at a filament temperature up to about 2600 °C for tantalum filament, which was much higher than the maximum filament temperature available for tungsten (2000 °C). The critical methane concentration in H₂-CH₄ gas for diamond deposition became higher with increasing filament temperature. A deposition rate about 20 times higher was obtained when using a tantalum filament compared with a tungsten filament. The origin of the improved deposition rate of diamond on WC-Co substrate using a tantalum filament is discussed.     

The adhesion of copper films deposited onto aluminum nitride

Good adhesion between copper film and AlN substrate is obtained when the surface of AlN is laser-irradiated prior to copper film deposition and post deposition annealing is conducted. Surface chemistry of AlN substrates before and after laser irradiation and the interfacial reactions of copper film/AlN couples were studied with Auger Electron Spectroscopy (AES) to understand the adhesion mechanisms. The surface of as-received AlN substrates was covered with a thin sheath of Al₂O₃. Laser irradiation removed the surface Al₂O₃ layers, smoothened the surface, and decomposed AlN leaving metallic aluminum on the surface. The interfacial reactions in the copper film/AlN couple are affected by the amounts of oxygen and metallic aluminum available at the interface. The adhesion mechanism is the formation of a Cu-O-Al compound at the interface of copper film/AlN couple. Since copper does not react with AlN, laser induced decomposition of AlN seems to be the driving force for the formation of the compound. This revised version was published online in September 2006 with corrections to the Cover Date.     

Substrate heating rates for planar and cylindrical-post magnetron sputtering sources

Substrate heating energies per atom deposited are reported for planar magnetron sputtering of aluminum, chromium, nickel, copper, molybdenum, indium, tantalum, tungsten and platinum in argon as well as for aluminum and chromium sputtered in O₂. Data are also reported for cylindrical magnetron sputtering of niobium, silver, tantalum, tungsten and Pb-Sn in argon as well as for molybdenum sputtered in neon, argon, krypton and xenon. The planar and cylindrical magnetron heating rates were comparable. The heating energies for argon sputtering ranged from 10–15 eV per deposited atom for the light metals to almost 100 eV atom^-1 for tantalum and tungsten. The implied reactive sputtering heating energies were about 500 eV molecule^-1 for Cr₂O₃ and 1150 eV molecule^-1 for Al₂O₃. Special experiments were conducted to examine the contributions to the substrate heating of plasma species and ion neutralization and reflection at the cathode. The data indicate that charged plasma species do not contribute significantly to the heating but that neutralized and reflected ions play a significant role in the planar as well as the cylindrical cases despite the differences in cathode geometry.     

Effect of substrate on the nucleation and growth of aluminum films deposited from methylpyrrolidine alane

Methylpyrrolidine alane complex was used to deposit aluminum films on various types of substrates in a low pressure chemical vapor deposition reactor. The films grow easily on metallic and transition metal oxide surfaces, but not on any other tested semiconductor and dielectric substrates below 200 °C, showing strong substrate dependency. The free energies of precursor adsorption, surface dissociation reaction and product desorption, as well as the film wettability to substrate are among the key factors which affect the energy barrier for nucleation or deposition selectivity. In general, a metal substrate can enhance nucleation because it catalyzes the surface reactions and bonds strongly with aluminum. The oxidation-reduction reaction may occur between the precursor and substrate on a metal oxide surface. The reduced metal sites can be the seed nuclei and are possibly responsible for Al growth on the surfaces of transition metal oxides.     

Tantalum chemical vapor deposition on substrates from various materials

Tantalum coatings have been produced for the first time by hydrogen-free chemical vapor deposition through reduction of tantalum pentabromide with cadmium vapor, which allowed the deposition temperature to be substantially reduced (by more than 200 K). The coatings consisted of α- and/or β-Ta, depending on the substrate material.     

Effects of low temperature on the characteristics of tantalum thin films

In this paper the effects of substrate temperature (room temperature - 350 °C) on the phase composition and crystallization orientation of the tantalum thin film deposited by direct current magnetron sputtering in an extremely low power deposition regime are presented. In this experiment, heating the substrates to 350 °C resulted in the growth of the hard and brittle tetragonal crystalline structure (β-Ta). Deposited tantalum has a conical structure with large voided boundaries. Sheet resistance of samples is much larger than for the convenient conductors which decreased with increasing the substrate temperature.     

Effects of low temperature on the characteristics of tantalum thin films

In this paper the effects of substrate temperature (room temperature – 350 °C) on the phase composition and crystallization orientation of the tantalum thin film deposited by direct current magnetron sputtering in an extremely low power deposition regime are presented. In this experiment, heating the substrates to 350 °C resulted in the growth of the hard and brittle tetragonal crystalline structure (β-Ta). Deposited tantalum has a conical structure with large voided boundaries. Sheet resistance of samples is much larger than for the convenient conductors which decreased with increasing the substrate temperature.     

Abscheidung leitender und nichtleitender Hartstoffschichten auf metallischen und keramischen Werkstoffen mittels Hochfrequenz-Plasma-CVD

Deposition of conductive and nonconductive hard coatings on metallic and ceramic materials by RF-PA-CVD Conductive titanium nitride and nonconductive aluminium oxide layers were deposited on conductive and nonconductive substrates by a RF-PA-CVD process. The influence of substrate material, pressure, plasma power and the components of the gas mixture on the layer properties was investigated. TiN coatings with a homogeneous structure could be deposited by using TiCl₄ as precursor. The properties of the layer are strongly influenced by the substrate material. An increasing pressure causes a faster deposition rate and a higher chlorine content. A lower chlorine content and at the same time a faster deposition rate can be achieved by increasing the r.f. power. Aluminium and aluminium oxide layers could be deposited on steel and Si₃N₄ substrates by using AlCl₃ as precursor in dependence on the CO₂ content in gas mixture. Higher CO₂ content facilitates the deposition of aluminium oxide.     

Vacuum deposited polymer/metal multilayer films for optical application

Vacuum-deposited polymer/silver/polymer reflectors and tantalum/polymer/aluminum Fabry-Perot interference filters were fabricated in a vacuum web coating operation on polyester substrates with a new, high-speed deposition process. Reflectivities were measured in the wavelength range from 0.3 μm to 0.8 μm. This new vacuum processing technique has been shown to be capable of deposition line speeds in excess of 500 linear m min⁻¹ (D.G. Shaw and M.G. Langlois, Proc. 7th Int. Conf. Vacuum Web Coating, November 1993, p. 268). Central to this technique is a new vacuum deposition process for the high-rate deposition of polymer films. This polymer process involves the flash evaporation of an acrylic monomer onto a moving substrate. The monomer is subsequently cured by an electron beam or ultraviolet light. This high-speed polymer film deposition process has been named the polymer multi-layer process. Also, vacuum-deposited, index-matched, polymer/CaF₂ composites were fabricated from monomer slurries that were subsequently cured with ultraviolet light. This second technique is called the liquid multi-layer process. Each of these polymer processes is compatible with each other and with conventional vacuum deposition processes such as sputtering or evaporation.     

Structural properties and morphology of Zn(1 − x)CdxO solid solution grown on ZnO and C-plane sapphire substrate

Zn_(1 − x)Cd_xO solid solutions with a composition ranging from pure ZnO up to x = 0.062 have been grown on ZnO and c-plane sapphire substrates by using metal organic chemical vapor deposition. The optical transmission spectra were used to estimate the cadmium mole fraction of the solid solutions. The lattice deformation and morphology of these films were examined in detail using high resolution X-ray diffraction and atomic force microscopy as Cd incorporation and used substrate. Our study reveals significant lattice deformation from x ≥ 0.7%. The atomic force microscopy images show facetted grains for films grown on ZnO substrate but rather round for c-plane sapphire substrate. The grain shape is controlled by the presence of the ionic charges on the polar surface of ZnO which is disturbed by cadmium incorporation and also the employed substrate material.     

Microstructural characteristics and carbon content of Al2O3 films as a function of deposition parameters

Microstructural characteristics and carbon content in aluminum oxide thin films deposited on silicon substrates are reported as a function of deposition parameters such as substrate temperature and molar concentration of the spraying solution. The films were deposited using the spray pyrolysis technique from a spraying solution of aluminum acetylacetonate (Al(acac)₃), dissolved in N,N-dimethylformamide (N,N-DMF), at temperatures in the range from 500 to 650 °C. Water mist was added during the deposition process and no further post deposition thermal treatments were given to these films. The films have a stoichiometry close to that expected for Al₂O₃, although, residual carbon from the deposition process was found to be present in these films. The surface roughness of the films was less than 20 , with deposition rates up to 540 /min, low chemical etch rates and activation energies around 27.6 kJ/mol were also determined. High resolution transmission electron microscopy observation of these films show the presence of a tiny 5Al₂O₃ : H₂O crystalline phase embedded in a dense amorphous matrix. It was found that the average crystallite diameter of this phase depended on the deposition temperature as well as on the molar concentration of the spraying solution.     

Flexible cadmium telluride/cadmium sulphide thin film solar cells on mica substrate

Polycrystalline thin film II–VI compound semiconductors of cadmium sulfide (CdS) and cadmium telluride (CdTe) are the leading materials for the development of cost effective and reliable photovoltaic systems. The two important properties of these materials are its nearness to the ideal band gap for photovoltaic conversion efficiency and they have high optical absorption coefficients. Usually thin film solar cells are made by hetero-junction of p-type CdTe with n-type CdS partner window layer. In this article, we have deposited CdTe films on mica substrates using thermal evaporation technique and CdTe/CdS junction were developed by depositing a thin layer of CdS on to the CdTe substrate from chemical bath deposition method. The device was characterized by current voltage and photocurrent spectroscopy technique prior to the deposition of the transparent conducting layer. The devices were annealed in air at different temperatures and found that the device annealed at 673?K had better photovoltaic parameters. The efficiency of a typical device under 50?mW?cm^?2 illumination was estimated as 4%.     

Growth of thin CdS films on glass substrates via reaction of thiourea with cadmium acetate in aqueous solution

Thin CdS films have been produced by chemical surface deposition from aqueous solutions of cadmium acetate, Cd(CH₃COO)₂. We have studied the morphology and optical properties of the CdS films and calculated the mechanical stress induced by the difference in linear thermal expansion coefficient between the film and substrate materials.     

Growth of cubic and hexagonal CdTe thin films by pulsed laser deposition

The paper reports the growth of cadmium telluride (CdTe) thin films by pulsed laser deposition (PLD) using excimer laser (KrF, λ=248 nm, 10 Hz) on corning 7059 glass and SnO₂-coated glass (SnO₂/glass) substrates at different substrate temperatures (T_s) and at different laser energy pulses. Single crystal target CdTe was used for deposition of thin films. With 30 min deposition time, 1.8- to ∼3-μm-thick films were obtained up to 200 °C substrate temperature. However, the film re-evaporates from the substrate surface at temperatures >275 °C. Atomic force microscopy (AFM) shows an average grain size ∼0.3 μm. X-ray diffraction analysis confirms the formation of CdTe cubic phase at all pulse energies except at 200 mJ. At 200 mJ laser energy, the films show hexagonal phase. Optical properties of CdTe were also investigated and the band gap of CdTe films were found as 1.54 eV for hexagonal phase and ∼1.6 eV for cubic phase.     

Mechanical and thermal properties of physical vapour deposited alumina films Part I Thermal stability

Thermal stability of non-reactive physical vapour deposited alumina films of varying thickness on Al₂O₃-TiC and Si substrates, deposited at two different substrate biases, is examined. Substrate curvature measurements were used to determine the deposition stress and stress development during thermal cycling and annealing. Thermal cycling experiments revealed that the films deposited on Al₂O₃-TiC substrates become irreversibly more compressive on heating and annealing while films deposited on Si substrates become irreversibly more tensile. The deposition stress was found to be independent of film thickness, substrate material, and substrate bias during deposition. The thermal stability was independent of film thickness and substrate bias during deposition.     

Reactively sputtered oxide optical coatings for inertial confinement fusion laser components

Results to date are presented for a study of reactively sputtered oxide optical coatings which are candidate materials for use in the NOVA Terawatt neodymium glass laser under development at Lawrence Livermore Laboratory, Livermore, California. Experimental details are described for the deposition of TiO₂ on fused silica substrates by r.f. diode sputtering of titanium in a reactive Ar-O₂ atmosphere. Specific deposition procedures are presented for variation of the phase composition and grain size of the coatings over wide ranges. High laser damage thresholds are reported for TiO₂, and glassy coatings appear to be more damage resistant than polycrystalline coatings. Phase composition appears to be less important to damage resistance than grain size. Application of the reactive sputtering process to preparation of damage-resistant oxides of In-Sn and tantalum is also described and damage thresholds obtained to date are reported.