Showing papers on "Chemical vapor deposition published in 1975"

Effects of vapor-phase deposition processes on the optical, chemical, and magnetic properties OE the lunar regolith

Abstract: The processes of solar wind sputtering and meteoritic impact vaporization have created materials in the lunar regolith which were deposited from a vapor phase. Although the quantity of such exotic condensed substances should theoretically be comparable with that of materials which have been melted by impacts, their existence in the fines has not been generally recognized. We have investigated the physical and chemical properties of materials deposited from vapors generated by hydrogen-ion sputtering and thermal evaporation of lunar and artificial ferrosilicates. Both processes are highly reducing. The deposits are enriched in Fe, have large, nonselective, optical absorptivities, and contain abundant sub-microscopic, superparamagnetic grains of metallic Fe which exhibit the characteristicg=2.1 ESR resonance. The sputter-deposited films are enriched in heavy elements. Thus the hypothesis that the lunar fines contain several percent of materials deposited from the vapor phase accounts in a natural manner for many of the unusual optical, physical and chemical properties of lunar soils. The vapor-deposits are probably concentrated in the agglutinate particles of the regolith.

Boron Nitride Composites By Chemical Vapor Deposition

Abstract: Composites of boron nitride (BN) have been made by the chemical vapor deposition (CVD) of a BN matrix on a BN felt fiber substrate. Reactant gases were boron trifluoride and ammonia. The composites have a relatively high density (1.70 g/cm3), a crystallite size LC = 150 A and an interlayer spacing d002 = 3.35 A. Measurements of elastic modulus and thermal conductivity and expansion showed some anisotropy as a result of the preferred fiber orientation of the substrate.

Chemical Processes in Vapor Deposition of Silicon I . Deposition from and Etching by

Abstract: Chemical processes occurring in the vapor deposition of Si from SiCl/sub 2/H/sub 2/ and in the etching of Si by HCl were studied by means of a mass spectrometer coupled to the chemical-vapor-deposition reactor. This setup was successfully used for the qualitative and quantitative analysis of the composition of the vapor phase in the Si-Cl-H system. Species found in the vapor phase were H/sub 2/, HCl, SiCl/sub 2/, SiCl/sub 2/H/sub 2/, SiCl/sub 3/H, and SiCl/sub 4/, and their partial pressures were measured as a function of temperature, Cl/H ratio, and of the chemical nature of the initial gaseous mixture entering the reactor. The experimentally determined partial pressures were compared with the equilibrium partial pressures of vapor species, calculated from the newest thermochemical data for the Si-Cl-H system. Based on these results, the nature and the extent of chemical processes in systems studied are discussed. (WDM)

Cadmium sulfide solar cells

Abstract: Development, fabrication and applications of CdS solar cells are reviewed in detail. The suitability of CdS cells for large solar panels and microcircuitry, and their low cost, are emphasized. Developments are reviewed by manufacturer-developer. Vapor phase deposition of thin-film solar cells, doping and co-evaporation, sputtering, chemical spray, and sintered layers are reviewed, in addition to spray deposition, monograin layer structures, and silk screening. Formation of junctions by electroplating, evaporation, brushing, CuCl dip, and chemiplating are discussed, along with counterelectrode fabrication, VPD film structures, the Cu2S barrier layer, and various photovoltaic effects (contact photovoltage, light intensity variation, optical enhancement), and various other CdS topics.

Dependence of resistivity on the doping level of polycrystalline silicon

Abstract: The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as−deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 1016 atoms/cm3 was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

Bulk superconductivity above 20 K in Nb 3 Ge

Abstract: The superconducting properties of bulk films(0.02- 0.06 mm thick) of Nb 3 Ge deposited on Cu substrates by chemical vapor deposition have been studied along with physical parameters characterizing these deposits. Results of susceptibility measurements showing superconducting onsets greater than 21 K and resistivity measurements showing onset greater than 22 K are presented along with heat capacity measurements. Data are also presented defining a relationship between superconducting transition temperature and lattice spacing throughout the range of 4 - 21 K. In addition, the effects of substrate temperature and substrate material, as well as mechanical properties such as substrate adherence are described.

Oxide nucleation on thin films of copper during in situ oxidation in an electron microscope

Abstract: single-crystalline thin films of copper were oxidized at an isothermal temperature of 425°C and at an oxygen partial pressure of 5×10−3 Torr in situ in a high-resolution electron microscope. The specimens were prepared by epitaxial vapor deposition onto polished {100} and {110} faces of rocksalt and mounted in a hot stage inside an ultra-high-vacuum specimen chamber of the microscope. Large amounts of sulfur, carbon, and oxygen were detected by Auger electron spectroscopy on the surface of the as-received films and were removed in situ by ion-sputter etching immediately prior to the oxidation. The nucleation and growth characteristics of Cu2O on Cu were studied. The predominantly observed crystallographic orientations of Cu2O on {100} and {110} copper films were epitaxial, parallel {100} and {110} orientations, respectively. In addition, a Cu2O {111} orientation with Cu2O 〈770〉//Cu 〈110〉 was found frequently on {100}-oriented copper films. The distinct particle shapes observed most frequently were square and hexagonal, representing {100} and {111} orientations, respectively. An induction period of about 30 min was found, which did not depend on the film thickness but did depend strongly on the oxygen partial pressure and the oxygen exposure prior to the oxidation. Neither stacking faults nor dislocations were found to be associated with the Cu2O nucleation sites. The growth of Cu2O nuclei was found to be linear with time. The experimental findings, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving (a) the formation of a surface-charge layer, (b) oxygen saturation in the metal and formation of a supersaturated zone near the surface, and (c) nucleation, followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Thin film formation of In2O3, TiN, and TaN by rf reactive ion plating

Abstract: In2O3, TiN, and TaN films were prepared on glass substrates by a rf ion‐plating technique. Indium, titanium, and tantalum were evaporated from evaporation sources in an oxygen or nitrogen atmosphere at a pressure on the order of 10−4 Torr. These films were observed to be pinhole free and uniform, showing excellent electrical and physical properties. The rf ion‐plating system appears to have some advantages over other methods of reactive deposition.

Means and method for inducing uniform parallel alignment of liquid crystal material in a liquid crystal cell

Abstract: Electrode surfaces are coated with a passivating material (silicon dioxide, aluminum oxide or titanium dioxide) or with a reflecting material (chromium or chromium and gold) or with a special alignment material (carbon) using standard vacuum sputtering, vacuum evaporation, electrodeposition, or chemical vapor deposition techniques. After sufficient thickness of material has been deposited, the substrate is exposed to a broad or narrow beam of neutralized argon ions of a few kilo-electron-volts energy. The beam of argon ions is incident at a grazing angle to the surface, typically 20°. Exposure of the overcoating results in a microscopic condition believed to comprise a "corrugated" surface with "ridges" and "valleys" parallel to the direction of the incident beam. These microscopically fine grooves or streaks are (1) reproducibly effective in causing parallel alignment of the liquid crystal molecules, (2) are durable to repeated cleaning procedures and air-bake treatments, and (3) are amenable to production applications in conjunction with vacuum deposition equipment.

Recrystallization processes in polycrystalline silicon

Abstract: Recrystallization processes in polycrystalline silicon made by a chemical vapor deposition technique have been investigated. Primary recrystallization has been observed between 1150 and 1250 °C, secondary recrystallization occurred above 1350 °C. By this procedure, grains of about 100 μm have been obtained. Recrystallized silicon can in principle be used as a substrate for making relatively inexpensive solar cells.

Structures of Si Films Chemically Vapor-Deposited on Amorphous SiO 2 Substrates

Abstract: Structural properties of Si films formed by chemical vapor deposition onto amorphous SiO2 substrates have been examined over the temperature and thickness ranges of 650 to 900°C and up to 1 µm respectively. At 650°C the films were amorphous regardless of their thickness. At 700°C the 0.1 µm-thick films were amorphous, but the preferred orientation developed as the film thickness increased. Above 750°C 0.1 µm-thick films were seen to have a random orientation, and with increasing film thickness above 0.3 µm, the and orientations developed in the temperature ranges of 750 to 825°C and 825 to 850°C respectively. The influence of heating at elevated temperatures on film strutucres is also presented.

Structure and electrical properties of CdS and CdTe thick films for solar cell applications

Abstract: CdTe/CdS heterojunction solar cells show particular promise for large‐scale terrestrial use. To evaluate these cells, thick films of CdTe and CdS have been grown and their structure and electrical properties determined. These films have been deposited on both single‐crystal and fused‐quartz substrates and on each other by close‐spaced vapor deposition in H2 and by two‐source vacuum evaporation. The influence of growth parameters on epitaxy and crystallite size was determined by scanning electron microscopy, and the electrical transport properties were investigated by conductivity and thermoelectric power measurements. The electrical mobility of the CdTe films on fused quartz shows an exponential dependence on E/kT, indicating that grain boundaries dominate the bulk mobility in the film. To achieve large crystallite sizes and high conductivity in reasonable deposition times, temperature/time profiles have been used to control nucleation and growth of the CdTe films. Post‐deposition heat treatments in H2 ha...

Alternating ion plating—A method of high‐rate ion vapor deposition

Abstract: Under certain circumstances, alternating ion plating (AIP) results in the same effects as conventional ion plating (IP). These conditions are satisfied if vapor and ions alternately act on each point of the substrate at rates and action times that are mutually adapted within each period. Based on energy situations in the coating process, it is then shown that energetic activation of the condensate can be enhanced by an increase in ion energy only within a limited range. Proper selection of the ionization arrangement, however, allows alternation of the ratio of ion to vapor rates and thus to change energetic activation by some orders of magnitude. An experimental setup for AIP is given. After that, nickel films produced by vapor deposition, pressure plating, and alternating ion plating are investigated with respect to some applicative features; i.e., optical reflectivity, corrosion resistance to H2S vapor, and protective action as per the Hutschenreuter porosity test. With reference to the examined properties, AIP gives the best results. According to the Hutschenreuter test, protective action increases with growing ion rate. The variation of optical reflectivity of the deposits is the same with AIP and the conventional IP technique. Expanded industrial application of IP calls for high depostion and ion rates, low working pressure, and adequate facilities for large‐area coating. One way to approach this goal is AIP with an ionization arrangement of the planar magnetron type. The possibilities of this technique are then outlined by way of the following parameter example: deposition rate 200 kA/min; energetic activation about 100 times higher than with vapor depostion; alternating frequencies up to some thousand cycles per minute.

Study of the diffusion of Au and Ag in Be using ion beams

Abstract: The diffusion of Au and Ag in single−crystal α−Be has been studied using ion beam techniques. The time−dependent diffusion profiles were monitored by ion backscattering. Diffusion couples were created both by ion implantation and by vapor deposition, with consistent results. Diffusion data were obtained at two temperatures, 665 and 780 °C, for both c and a crystallographic directions. Because of the low solid solubilities of Au and Ag in Be, ≲0.1 at.% at the above temperatures, a surface layer of ∼ 1000 A thickness was always present in which the solubility was greatly exceeded. During annealing this layer served as a source from which the solute diffused into the underlying Be. The surface layer was characterized by transmission electron microscopy in the case of Au implantation. No evidence of precipitation was found following the room−temperature implantation, but subsequent annealing above about 300 °C caused regions of AuBe5 to form in the layer. In the underlying bulk, the observed diffusion behavio...

Planar insulation of conductive patterns by chemical vapor deposition and sputtering

Abstract: A method using a chemically vapor deposited (CVD) insulator to form a substantially planar layer of insulative material atop a conductive pattern on the surface of a substrate. The invention also features the use of a photoresist both as a mask for forming apertures in an underlying insulating layer as well as a lift-off material for a subsequently deposited conductive layer. In the method, a first insulating layer is deposited atop the substrate. Photoresist is then deposited; the resist pattern is exposed and developed; and the insulator is etched to expose selected areas of the substrate. A conductive film, preferably metal, is then deposited in blanket fashion in such quantity as to achieve the same height as the first insulator within the exposed apertures. The resist is lifted off, thereby leaving metal in the exposed apertures only. The pattern at this point consists of a single level of a conductive pattern and the insulator pattern with gaps between the conductors and the insulator. The gaps are the result of the unavoidable removal of a portion of the insulator below the photoresist during the etching process. Another insulating film is chemically vapor deposited (pyrolytically deposited) in blanket fashion. Notwithstanding the gaps between the conductors and first insulator, the second film is substantially planar if the thickness of this second insulating film equals or exceeds one-half the width of the largest of said gaps. The method is applicable to any level of conductive patterns (metallization) atop the substrate.

Thick semiconductor films for photothermal solar energy conversion

Abstract: Efficient and economical photothermal conversion of solar energy requires the use of spectrally selective surfaces for collection and retention of incident solar flux. This spectral selectivity can be obtained from an absorber–reflector tandem by overcoating an opaque metal film having high infrared reflectance with a thick film (1–5μm) of semiconductor having an appropriate band gap. The practical implementation of this design using films of silver and silicon on a variety of substrate materials is described. Chemical vapor deposition (CVD) is used for depositing the absorber and the antireflection layers. The spectral reflectance of coated samples has been measured at temperatures up to 500 °C and gives α/e values in the range of 12–15, with a solar absorptance of 75%. The solar absorptance increases with temperature, while the thermal emittance typically increases by 2%–4% at 500 °C. Both the film adhesion and the spectral reflectance have remained stable after over 2000 cycles to 450 °C.

Some properties of chemically vapor deposited films of AlxOyNz on silicon

Abstract: Transmission electron microscopy (TEM) studies of films prepared in the AlN-Al2O3 pseudobinary system by chemical vapor deposition (as described in a companion paper entitled, “Chemical Vapor Deposition of AlxOyNz Films”) indicates that four different phases can be obtained by altering the NH3/CO2 gas ratio and preparation temperature. Films prepared at 900°C yield three polycrystalline phases and an amorphous composition. From zero to 25 at. percent O an AlN phase is observed. Amorphous material is observed from 25 to 47 at. percent O. From 47 to 59 at. percent O an AlxOyNz spinel is observed. At 60 at. percent O (pure Al2O3) an alumina phase is observed (KI phase). For 770°C films the AlN phase is observed from zero to 8 at. percent 0; from 8 to 23 at. percent O the zeta-alumina phase is seen; and at 60 at. percent O the KI alumina phase is again observed. For both the 770 and 900°C films, the grain size of the AlN phase was found to decrease with increasing oxygen content.

Graphite fiber/metal composites

Abstract: A novel graphite fiber/metal composite material in which the graphite fibers have an adherent coating of silicon oxide and silicon carbide. The coating protects the graphite surface from attack by carbide forming matrix metals such as aluminum, titanium, magnesium and nickel. In a preferred embodiment of the invention the coating is formed by an intermediate temperature vapor deposition technique involving the reduction of silicon tetrachloride in the presence of hydrogen and an oxygen containing gas.