Showing papers on "Chemical vapor deposition published in 1980"

Dopant segregation in polycrystalline silicon

Abstract: Dopant segregation at grain boundaries in polycrystalline silicon has been investigated. Arsenic, phosphorus, and boron were ion implanted into low‐pressure, chemically‐vapor‐deposited polycrystalline‐silicon films. All films were then annealed at 1000 °C for 1 h, and some were subsequently further annealed at 800, 850, or 900 °C for 64, 24, or 12 h, respectively. For phosphorus and arsenic the room‐temperature resistivity of the films was found to be higher after annealing at lower temperatures. By successively annealing the same sample at lower and higher temperatures, the resistivity would repeatedly increase and decrease, indicating reversible dopant segregation at the grain boundaries. Hall measurements were used to estimate the number of active dopant atoms within the grains and the number of atoms segregated at the grain boundaries as a function of annealing temperature. A theory of segregation in systems of small particles has been developed. Using this theory, the heat of segregation of arsenic and phosphorus in polycrystalline silicon was calculated. For boron no appreciable segregation was observed.

Preparation of conducting and transparent thin films of tin‐doped indium oxide by magnetron sputtering

Abstract: High‐quality 800‐A‐thick films of tin‐doped indium oxide have been prepared by magnetron sputtering. It is shown that films with low resistivity (∼4×10−4 Ω cm) and high optical transmission (≳85% between 4000 and 8000 A) can be prepared on low‐temperature (40–180 °C) substrates with O2 partial pressures of (2–7)×10−5 Torr.

Chemical Vapor Deposition of Single Crystalline β ‐ SiC Films on Silicon Substrate with Sputtered SiC Intermediate Layer

Abstract: A single crystal of was grown by chemical vapor deposition using an system on a silicon substrate with a sputtered layer. The grown layer of 4 μm thickness was confirmed as a single crystal by examination with reflection electron diffraction and x‐ray diffraction. To reduce the large mismatch between and a silicon substrate, a sputtered layer was employed as a buffer layer. Even though the sputtered layer was polycrystalline, the subsequent layer deposited by CVD was a single crystal. The crystallinity of the deposited layer was strongly affected by the thickness of the sputtered layer, the substrate temperature during sputtering, and the temperature of chemical vapor deposition.

Structure and Properties of LPCVD Silicon Films

Abstract: Silicon films deposited by low pressure chemical‐vapor deposition over the temperature range from 525° to 725°C were investigated. It was found that polycrystalline films are formed above 600°C and are more stable than the amorphous films deposited at lower temperatures. Their crystal structure is a strong function of the deposition temperature and a weaker function of the deposition rate. Either the {110} or the {100} texture may dominate the structure, depending primarily on the deposition temperature. The electrical resistance obtained on doping the LPCVD films that are polycrystalline as deposited is maximum for films deposited at the lower temperatures (near 600°C), although this dependence on deposition temperature decreases after annealing at higher temperatures. Dopant atoms reversibly segregate to the grain boundaries during lower temperature heat‐treatments subsequent to doping and are dispersed at higher temperatures, with corresponding changes in resistivity. The oxidation rate is only a weak function of the deposition temperature, although the initially amorphous films may oxidize somewhat more rapidly. The index of refraction of amorphous films is significantly higher than that of polycrystalline films.

A technique for producing epitaxial films on reuseable substrates

Abstract: Using a new technique, which we have named the CLEFT process (cleavage of lateral epitaxial films for transfer), we have grown single‐crystal GaAs films by vapor phase epitaxy (VPE) on reusable GaAs substrates. A carbonized photoresist mask with narrow, widely spaced stripe openings is first deposited on a (110) GaAs substrate. Epitaxial growth initiated within the openings, followed by lateral growth over the mask, produces a continuous single‐crystal GaAs film. The upper surface of the film is bonded to a glass substrate, and the film is then cleaved from the GaAs substrate, leaving the surface of the latter in condition for repeating the procedure. The same GaAs substrate has been used for successive growth of four GaAs films, each about 4 cm2, ranging in thickness from 5 to 10 μm. The electrical properties of a CLEFT film were found comparable to those of conventional VPE layers. The CLEFT process should also be applicable to other semiconductors.

Growth of Epitaxial ZnO Thin Films by Organometallic Chemical Vapor Deposition

Abstract: Organometallic chemical vapor deposition of on sapphire, using the reaction of diethylzinc with , , and oxidizing gas systems, has been studied. Epitaxial films have been achieved at temperatures of 400° and 730°C, respectively, in the first two systems. The films have been characterized using scanning electron microscopy (SEM), reflection electron diffraction (RED), and surface acoustic wave techniques.

High current injection into SiO2 from Si rich SiO2 films and experimental applications

Abstract: Chemically vapor deposited (CVD) Si rich SiO2 layers on thermal or CVD SiO2 layers incorporated into metal‐insulator‐semiconductor (MIS) capacitor structures are shown to give very large injected electron currents at low to moderate negative gate voltage biases. The dependence of this injection mechanism on the Si rich SiO2 composition and thickness, temperature, capacitor area, annealing conditions, gate metal (Al or Au), and underlying SiO2 thickness is described. Photocurrent measurements are discussed and are shown to give similar barrier energies as seen for ’’uniform’’ internal photoemission into SiO2. From the experimental electrical and photoelectrical measurements described here and transmission electron microscopy (TEM) and Auger studies of others, a possible model to explain this phenomenon based on electric field distortion caused by a two phase mixture of amorphous Si and SiO2 is presented. Two experimental applications of these structures are described. In one application, an electrically al...

Thermophoretic Deposition of Small Particles in the Modified Chemical Vapor Deposition (MCVD) Process

Abstract: Thermophoresis is conclusively established as the particulate deposition mechanism in the MCVD process by comparing experimental measurements and quantitative theoretical predictions. The deposition efficiency, E, is defined as the fraction of the silica in the gas stream (initially as SiCl4) that is deposited. For normal MCVD operating conditions, the deposition efficiency is only a function of the equilibrium temperature, Te, at which the gas and walls equilibrate downstream of the torch and the temperature, Tr, at which reaction occurs. The deposition efficiency is ∼0.8[1-(Te/Tr)]. It is determined that Te is a strong function of the torch traverse velocity, the traverse length, the temperature of the ambient environment, and the tube wall thickness but only a weak function of the gas flow rate. At high gas flow rates, the efficiency is limited by incomplete reaction.

Low temperature process for depositing oxide layers by photochemical vapor deposition

Abstract: The specification discloses a low temperature process for depositing oxide layers on a substrate by photochemical vapor deposition, by exposing the substrate to a selected vapor phase reactant in the presence of photochemically generated neutral (un-ionized) oxygen atoms. The oxygen atoms react with the vapor phase reactant to form the desired oxide, which deposits as a layer on the substrate. The use of photochemically generated neutral oxygen atoms avoids damage to the substrate due to charge bombardment or radiation bombardment of the substrate. The deposited oxide layer may optionally incorporate a selected dopant material in order to modify the physical, electrical, or optical characteristics of the oxide layer.

Highly oriented zinc oxide films grown by the oxidation of diethylzinc

Abstract: Zinc oxide films, with a high degree of c‐axis orientation, have been grown on glass substrates by a chemical vapor deposition process involving the oxidation of diethylzinc. Film growth was carried out over the 200–500 °C temperature range; however, the maximum crystal orientation was found to occur with substrate temperatures between 325 and 400 °C. The effect of different substrate materials on crystallographic orientation is also described in this letter.

Silicon Deposition on a Rotating Disk

Abstract: A one‐dimensional model has been developed which describes the interactions among hydrodynamics, multicomponent heat and mass transfer, and reaction kinetics for the rotating disk system. The analysis includes variable physical properties and finite interfacial velocity and has provision for an arbitrary number of simultaneous homogeneous and heterogeneous reactions. The model has been applied to the chemical vapor deposition of silicon from silicon tetrachloride in excess hydrogen. Predictions for the dependence of silicon production rate on disk temperature and rotation rate are compared with available experimental data.

Method for producing devices comprising high density amorphous silicon or germanium layers by low pressure CVD technique

Abstract: Layers of controllably dopable amorphous silicon and germanium can be produced by means of low pressure chemical vapor deposition, at a reaction temperature between about 450° C. and about 630° C., for Si, and between about 350° C. and about 400° C. for Ge, in an atmosphere comprising a Si-yielding or Ge-yielding precursor such as SiH 4 or GeI 4 , at a pressure between about 0.05 Torr and about 0.7 Torr, preferably between about 0.2 and 0.4 Torr. For undoped Si and P-doped Si, the preferred temperature range is from about 550° C. to about 630° C., for B-doped Si, it is from about 480° C. to about 540° C. The material produced has a density in excess of 0.9 of the corresponding crystalline density, and contains less than 1 atomic percent of hydrogen. An advantageous doping method is addition of dopant-forming precursor, e.g., PH 3 or B 2 H 6 , to the atmosphere. The material produced can be transformed into high quality crystalline material, and has many device applications in amorphous form, e.g., in solar cells, vidicon tubes, photocopying, and in integrated circuits, either as a conductor or nonconductor. The layers produced show conformal step coverage.

Elastic stiffness and thermal expansion coefficient of BN films

Abstract: Room temperature stresses were found to be tensile for chemical vapor deposition films of the composition B2N and compressive for BN, with all films becoming more tensile with heating. Analyses of the stress‐temperature curves of identical films of BN deposited on two different substrate materials yield values of 1.3×1012 dynes/cm2 for the elastic stiffness parameter E/(1−ν) and 1.0 ppm/°C for the thermal expansion coefficient. This technique is of general applicability to thin films and it is believed to be the first practical (nondestructive) means of determining both the elastic stiffness parameter and thermal expansion coefficient of a film.

Energy distribution of trapping states in polycrystalline silicon

Abstract: The electronic density of states in the forbidden gap of polycrystalline silicon has been determined from an analysis of capacitance and conductance of a Metal/SiO2 (∼60 A)/polycrystalline silicon(∼250 A)/Si(111) (MOSS) structure. In this structure the thickness of the polycrystalline silicon is comparable to its grain size. Net density of trapped charges in the polycrystalline silicon is enough to terminate the electric field penetrating from the oxide layer. Then, two‐terminal admittance of the MOSS structure is dominated by charging or discharging of the trapping states in a wide range of applied gate bias. The U‐shaped distribution of trapping state density has been found for thin polycrystalline silicon films.

White photoluminescence of amorphous silicon‐carbon alloy prepared by glow‐discharge decomposition of tetramethylsilane

Abstract: An amorphous film of silicon‐carbon alloy with approximate composition Si0.1C0.9 was prepared on a fused‐quartz, a glass, or a silicon wafer by the glow‐discharge decomposition of tetramethylsilane. The film has an optical gap energy as large as 2.8 eV and shows white photoluminescence even at room temperature due to its broad emission band over the whole range of the visible spectrum. The photoluminescence is observable for the films deposited at substrate temperatures below 300 °C.

Modified chemical vapor deposition of an optical fiber using an rf plasma

Abstract: The modified chemical vapor deposition process is practiced using an rf source as the external heat source. An rf plasma is thus established within a glass tube through which appropriate glass precursor vapors are passed. As a result of the ensuing chemical reactions, particulate material is formed within the tube and deposits on it. The hot plasma zone may be used to consolidate this particulate material into a transparent glass, and onto the interior wall of the tube. The tube is subsequently drawn into an optical fiber.

Fabrication of optical waveguides by the outside vapor deposition process

Abstract: The outside vapor deposition process (OVD) represents one of the principle vapor deposition methods used to make glass fiber optical waveguides [1], [2]. In this brief review, each of the basic process steps (deposition, sintering, drawing) are described and the present performance capabilities are presented. Process improvements leading to hydroxyl removal, increased numerical aperture (NA), and long wavelength operation are discussed. Selected examples of fiber compositions and properties are tabulated which range from high-NA fibers suitable for short-distance applications through very-high-performance fibers for long-distance transmission.

Epitaxial alignment of polycrystalline Si films on (100) Si

Abstract: We demonstrate that fine‐grained polycrystalline Si films obtained by chemical vapor deposition can be aligned expitaxially with respect to the underlying (100) Si substrate upon furnace annealing at temperatures of 1000–1150 °C. The alignment proceeds basically by the formation of epitaxial columns which subsequently grow laterally to consume the remaining polycrystalline Si. The rates of alignment are measured to be 20–200 A/min in the temperature interval of annealing with an activation energy of 4.7 eV. The epitaxial layers so obtained are of reasonably good crystal quality and contains only a small amount of planar crystallographic defects.

Temperature dependence of stresses in chemical vapor deposited vitreous films

Abstract: Thermal stresses in chemical vapor deposited (CVD) vitreous silicate and phosphosilicate glass (PSG) films on Si substrates are measured in situ from room temperature (RT) to 900 °C. As‐deposited films grown at one atmospheric (APCVD) and lower pressures (LPCVD) are found to be inherently under a tensile and compressive stress at RT, respectively. On heating to 500 °C, the tensile component of the stress develops in both CVD films. Tensile stress increases with time at a given temperature. In the range 500–900 °C, the tensile component is reduced with temperature and time. During the cooling process from a temperature between 700 and 900 °C, the stress component of APCVD and LPCVD films changes from tension to compression. With APCVD film, the temperature dependence of the stress in the range RT–500 °C can be represented as a function of phosphorous concentration in mol % P2O5. Temperature and time dependence, and thermal hysteresis are attributable to water content, sintering, and viscoelastic properties of CVD film. These are explained from the viewpoint of glass annealing and softening temperature points.

Laser‐induced chemical vapor deposition of polycrystalline Si from SiCl4

Abstract: Polycrystalline Si films with average grain sizes of ∼8 μm have been grown by laser‐induced chemical vapor deposition from SiCl4. A cw CO2 laser operated at 10.6 μm was used to provide local heating of quartz substrates in an otherwise cool reactor to initiate the endothermic decomposition reaction. Deposition rates of 5.1 μm/min were obtained for films grown at an incident laser power of 18.9 W, resulting in sharply defined mesa structures due to the occurrence of the reverse reaction, etching of free Si, at cooler regions of the substrate surface closer to the edge of the 6‐mm irradiated zone. The diameter of the mesas was 1.4 mm with thicknesses up to 26 μm. Three modes of film growth, depending on the incident laser power, were observed.

Observation of amorphous silicon regions in silicon‐rich silicon dioxide films

Abstract: Raman scattering and optical transmission measurements have been made on chemically vapor‐deposited Si‐rich SiO2 films. The measurements show segregated regions of amorphous silicon in the as‐deposited films. Annealing the films at 1150 °C completely crystallizes the amorphous silicon. Annealing at lower temperatures produces films with both amorphous and crystalline regions.

Radiation heated reactor process for chemical vapor deposition on substrates

Abstract: A method of chemically vapor depositing a material on a plurality of stacked substrates comprising heating a tubular susceptor surrounding the stack to thereby heat the substrates by radiant heating.

Deposition rate and rate-limiting steps in the chemical vapour deposition of boron in a closed system

Abstract: The deposition rate of boron in a closed chemical vapour deposition system was investigated. Various methods for the determination of deposition rates are outlined. Values for the apparent activation energy of the deposition process were found to lie in the range 100–1000 kJ mol−1. An apparent activation energy value of 100 kJ mol−1 indicates that the deposition rate is controlled partly by diffusion and partly by surface kinetics. It is concluded that, in the range 121–218 kJ mol−1, the process is limited by two concurrent surface kinetics mechanisms. Apparent activation energy values higher than 218 kJ mol−1 indicate that nucleation becomes an important rate-limiting step. At approximately 1000 kJ mol−1 the process is completely controlled by nucleation. Finally, the origin of various morphologies of the boron deposit is discussed in connection with a schematic kinetics curve.

Electrical properties of polycrystalline GaAs films

Abstract: Electrical properties of Se‐ and Zn‐doped polycrystalline GaAs deposited by metalorganic chemical vapor deposition on substrates of polycrystalline alumina and glass were investigated. Hall‐effect and resistivity measurements were made over a wide range of temperature (77–420 K). The electrical activation energies were found by measuring the variation of resistivity and carrier mobility of the polycrystalline GaAs films with sample temperature. The resistivity and mobility were found to be temperature activated over a wide temperature range as exp(Eb /kT) and exp(−Eb /kT), respectively, with the same activation energy applying to both properties. The results have been interpreted in terms of a modified grain boundary trapping model.