Showing papers on "Chemical vapor deposition published in 1997"

Heat transport in thin dielectric films

Abstract: Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3ω method. SiO2 and SiNx films are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films >100 nm thick, the thermal conductivity shows little dependence on film thickness: the thermal conductivity of PECVD SiO2 films is only ∼10% smaller than the conductivity of SiO2 grown by thermal oxidation. The thermal conductivity of PECVD SiNx films is approximately a factor of 2 smaller than SiNx deposited by atmospheric pressure CVD at 900 °C. For films <50 nm thick, the apparent thermal conductivity of both SiO2 and SiNx films decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistance RI. At room temperature, RI∼2×10−8 K m2 W−1 and is equivalent to the thermal resistance of a ∼20 nm thick layer of SiO2 .

Growth of p-type Zinc Oxide Films by Chemical Vapor Deposition

Abstract: The growth of p-type ZnO film was realized for the first time by the simultaneous addition of NH3 in carrier hydrogen and excess Zn in source ZnO powder. The resistivity was typically 100 Ωcm. A model showing nitrogen incorporation suggests the possibility of realizing p-type ZnO film of low resistivity by optimizing thermal annealing.

Step-controlled epitaxial growth of SiC: High quality homoepitaxy

Abstract: Chemical vapor deposition (CVD) of silicon carbide (SiC) onto SiC{0001} substrates and its device applications are reviewed. Polytype-controlled epitaxial growth of SiC, which utilizes step-flow growth on off-oriented SiC{0001} substrates (step-controlled epitaxy), is proposed, and the detailed growth mechanism is discussed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layer. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the surfaces of SiC epilayers, nucleation, and step-dynamics are also investigated. The high quality of SiC epilayers was elucidated through low-temperature photoluminescence, Hall effect, and deep level measurements. Excellent doping controllability over a wide range was obtained by in situ doping of a nitrogen donor and aluminum/boron acceptors. Recent progress in SiC device fabrication using step-controlled epitaxial layers is presented. The intrinsic potential of SiC is demonstrated in the excellent performance of high-power, high-frequency, and high-temperature devices, which will develop novel electronics.

Correlation of cathodoluminescence inhomogeneity with microstructural defects in epitaxial gan grown by metalorganic chemical-vapor deposition

Abstract: We discuss the relationship between microstructure and luminescence efficiency for heteroepitaxial films of GaN grown on c-axis sapphire substrates by metalorganic chemical-vapor deposition. We directly characterize the correlation between threading dislocations as observed by transmission electron microscopy, surface morphology as observed by atomic force microscopy, and wavelength-resolved cathodoluminescence imaging. We show that the inhomogeneity in the luminescence intensity of these films near band edge can be accounted for by a simple model where nonradiative recombination at threading dislocations causes a deficiency of minority carriers and results in dark regions of the epilayer. An upper bound for average diffusion length is estimated to be 250 nm.

Growth and characterization of phosphorous doped {111} homoepitaxial diamond thin films

Abstract: An n-type semiconducting diamond thin film was obtained by microwave enhanced plasma chemical vapor deposition using phosphine (PH3) as a dopant source. A homoepitaxial diamond thin film with a thickness of about 300 nm was grown on the {111} surface of a type Ib diamond with a variety of dopant concentrations. Over a wide range of dopant concentrations (PH3/CH4: 1000–20 000 ppm), the n-type conduction was confirmed by Hall-effect measurements. The activation energy of carriers was 0.43 eV. The Hall mobility of about 23 cm2/V s has been obtained at around 500 K for the 1000 ppm sample. No significant increase of hydrogen has been observed by secondary-ion-mass-spectroscopy analysis for the phosphorous doped layers.

The dielectric response as a function of temperature and film thickness of fiber-textured (Ba,Sr)TiO3 thin films grown by chemical vapor deposition

Abstract: The temperature- and field-dependent permittivities of fiber-textured Ba0.7Sr0.3TiO3 thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness. These films display a nonlinear dielectric response under conditions representative of those encountered in dynamic random access memories or other integrated capacitor applications. This behavior has the exact form expected for a classical nonlinear, nonhysteretic dielectric, as described in terms of a power series expansion of the free energy in the polarization as in the Landau–Ginzburg–Devonshire approach. Curie–Weiss-like behavior is exhibited above the bulk Curie point (∼300 K), although the ferroelectric phase transition appears frustrated. Small-signal capacitance measurements of films with different thicknesses (24–160 nm) indicate that only the first term in the power series expansion varies significantly with film thickness or temperature. Possible origins for this thickness dependence are...

Apparatus and method for preventing the premature mixture of reactant gases in CVD and PECVD reactions

Abstract: A method and apparatus for depositing a film by chemical vapor deposition comprises a showerhead for dispersing reactant gases into the processing space wherein the showerhead has a first space therein operable for receiving and dispersing the first reacting gas, and has a second space therein, generally isolated from the first space, and operable for receiving and dispersing the second reactant gas separate from the first gas dispersion for maintaining segregation of reactant gases and generally preventing premature mixture of the gases prior to their introduction into the processing space to prevent premature deposition in the system.

Leakage currents in Ba0.7Sr0.3TiO3 thin films for ultrahigh-density dynamic random access memories

Abstract: (Ba,Sr)TiO3 (BST) thin films grown by chemical vapor deposition and with platinum (Pt) top and bottom electrodes have been characterized with respect to the leakage current as a function of temperature and applied voltage. The data can be interpreted via a thermionic emission model. The Schottky approximation accounts for superohmic behavior at higher fields, but the barrier lowering is stronger than expected from this theory. While the leakage mechanism is comparable to SrTiO3 thin films prepared by chemical solution deposition, the absolute values of the leakage current are significantly lower for the metalorganic chemical vapor deposition (MOCVD) prepared BST film. This is presumably due to a more homogeneous microstructure of the latter and may also be due to different electrode processing. The influence of the film thickness on the leakage in combination with additional findings is used to discuss the field distribution in the films under a dc voltage stress.

Room-temperature continuous-wave lasing from stacked InAs/GaAs quantum dots grown by metalorganic chemical vapor deposition

Abstract: We report on quantum dot (QD) lasers made of stacked InAs dots grown by metalorganic chemical vapor deposition. Successful growth of defect-free binary InAs/GaAs QDs with high lateral density (dl⩾4×1010 cm−2) was achieved in a narrow growth parameter window. The room-temperature photoluminescence (PL) intensity is enhanced up to a factor of 3 and the PL peak width is reduced by more than 30% when a thin layer of In0.3Ga0.7As is deposited onto the InAs QDs. A QD laser with a single sheet of such InAs/InGaAs/GaAs QDs exhibits threshold current densities as low as 12.7 and 181 A/cm2 at 100 and 300 K, respectively. Lasers with threefold stacked QDs show ground-state lasing and allow for cw operation at room temperature.

Deposition of three-dimensional Ge islands on Si(001) by chemical vapor deposition at atmospheric and reduced pressures

Abstract: This report summarizes observations of Ge island formation during growth on Si(001) by chemical vapor deposition from germane in the pressure range from 10 Torr to atmospheric pressure in a conventional epitaxial reactor. A four-step growth process is observed: (1) uniform pseudomorphic overlayer (“wetting’’ layer) formation; (2) three-dimensional island growth with a constant aspect ratio; (3) continued island growth with a constant diameter and increasing height; (4) rapid growth of larger, faceted islands. Ostwald ripening of the islands during continued heat treatment after terminating the deposition is slow compared to island formation and growth during deposition for the experimental conditions used.

Optical properties of hexagonal GaN

Abstract: Single-crystalline hexagonal GaN (α-GaN) films have been grown on (0001) sapphire substrates by metalorganic chemical vapor deposition at 1040 °C. The complex dielectric functions, e(E)=e1(E)+ie2(E), of the epitaxial films have been measured by spectroscopic ellipsometry (SE) for E⊥c in the region between 1.5 and 5.0 eV at room temperature. Previously published ultraviolet SE spectra of α-GaN are examined by considering the effects of surface roughness using an analysis based on an effective medium model. Ex situ atomic force microscopy is used to assess independently surface flatness. By mathematically removing the effects of surface roughness, the most reliable e(E) values for α-GaN are presented in the 1.25–10 eV photon–energy range. Theoretical dispersion analysis suggests that the E0 structure could be characterized by a three-dimensional M0 critical point and the E1α (α=A,B,C) structures by two-dimensional M1 critical points. To facilitate design of various optoelectronic devices, dielectric-functio...

Single-crystal Pb(ZrxTi1−x)O3 thin films prepared by metal-organic chemical vapor deposition: Systematic compositional variation of electronic and optical properties

Abstract: Single-crystal thin films of Pb(ZrxTi1−x)O3 (PZT) covering the full compositional range (0⩽x⩽1) were deposited by metal-organic chemical vapor deposition. Epitaxial SrRuO3(001) thin films grown on SrTiO3(001) substrates by rf-magnetron sputter deposition served as template electrode layers to promote the epitaxial growth of PZT. X-ray diffraction, energy-dispersive x-ray spectroscopy, atomic force microscopy, transmission electron microscopy, and optical waveguiding were used to characterize the crystalline structure, composition, surface morphology, microstructure, refractive index, and film thickness of the deposited films. The PZT films were single crystalline for all compositions exhibiting cube-on-cube growth epitaxy with the substrate and showed very high degrees of crystallinity and orientation. The films exhibited typical root mean square surface roughness of ∼1.0–2.5 nm. For tetragonal films, the surface morphology was dominated by grain tilting resulting from ferroelectric domain formation. We r...

16.0% Efficient Thin-Film CdS/CdTe Solar Cells

Abstract: High efficiency cadmium sulfide (CdS)/cadmium telluride (CdTe) solar cells have been developed using ultrathin CdS films having a thickness of 50 nm. CdS films deposited on indium tin oxide (ITO)/#1737 glass substrates by the metal organic chemical vapor deposition technique, and CdTe films subsequently deposited by the close-spaced sublimation technique were used for the fabrication of CdS/CdTe solar cells. A photovoltaic conversion efficiency of 16.0% under Air Mass (AM) 1.5 conditions has been measured by the Japan Quality Assurance Organization.

Method of surface treatment of semiconductor substrates

Abstract: This invention relates to methods for treatment of semiconductor substrates and in particular a method of etching a trench in a semiconductor substrate in a reactor chamber using alternatively reactive ion etching and depositing a passivation layer by chemical vapour deposition, wherein one or more of the following parameters: gas flow rates, chamber pressure, plasma power, substrate bias, etch rate, deposition rate, cycle time and etching/deposition ratio vary with time.

Investigation of the effect of hydrogen on electrical and optical properties in chemical vapor deposited on homoepitaxial diamond films

Abstract: We have investigated electrical and optical properties of the high-conductivity layers formed in both undoped and B-doped diamond films prepared by chemical vapor deposition. It is found that both hydrogenated undoped and B-doped diamond films have high-concentration holes of ∼1018 cm−3 at 297 K. These films exhibit little temperature dependence of the hole concentration between 120 and 400 K, while that of the oxidized B-doped film has a strong temperature dependence with an activation energy 0.38 eV. The Hall mobility of all the hydrogenated films of ∼30 cm2/Vs at 297 K is one to two orders of magnitude smaller than that of the oxidized B-doped film and increases with increasing temperature. The I−V characteristics of Al–Schottky contacts to the hydrogenated undoped film show excellent rectification properties and the temperature dependence of their forward characteristics is well explained by a junction theory inclusive of the tunneling process, i.e., thermionic-field emission theory, indicating that the depletion layer becomes thin due to high-density space charge in the depletion layer. We have also found a broad cathodoluminescence peak at around 540 nm in the hydrogenated films which disappears with subsequent oxidation treatment, indicating the existence of hydrogen-related gap states in the subsurface region of as-deposited homoepitaxial diamond films. High density hydrogen is detected in the subsurface region of the hydrogenated films by secondary ion mass spectroscopy. These experimental results suggest the existence of hydrogen-induced shallow acceptors in the surface region of as-deposited (hydrogenated) diamond films and that the difference between the hydrogenated and the oxidized films observed in both electrical and optical properties originates from hydrogen incorporated in the subsurface region.

Multi-step high density plasma chemical vapor deposition process

Abstract: A method for depositing dielectric material into gaps between wiring lines in the formation of a semiconductor device includes the deposition of three oxide layers using high density plasma chemical vapor deposition (HDPCVD). A first HDPCVD step is carried out while keeping the substrate unbiased to form an oxide layer over the lines and in the gap. A second HDPCVD step in which the substrate is biased deposits a second oxide layer over the first oxide layer. During the second HDPCVD step some etching occurs and a portion of the first oxide layer is removed. A third HDPCVD step is carried out at a greater etch and sputtering rate than the second step to complete filling of the gap with dielectric material. The first oxide layer acts to protect the underlying structures from etching damage during the third step. Gaps between wiring lines can be filled with dielectric material without forming voids, even for high aspect ratio gaps.

Digital chemical vapor deposition (CVD) method for forming a multi-component oxide layer

Abstract: A chemical vapor deposition (CVD) method for forming a multi-component oxide layer. There is first provided a chemical vapor deposition (CVD) reactor chamber. There is then positioned within the chemical vapor deposition (CVD) reactor chamber a substrate. There is then formed over the substrate a multi-component oxide precursor layer. The multi-component oxide precursor layer is formed from at minimum a first precursor reactant source material and a second precursor reactant source material introduced simultaneously into the chemical vapor deposition (CVD) reactor chamber in absence of an oxidant reactant source material. There is then oxidized with the oxidant reactant source material within the chemical vapor deposition (CVD) reactor chamber the multi-component oxide precursor layer formed over the substrate to form a multi-component oxide layer formed over the substrate. The oxidant reactant source material is introduced into the chemical vapor deposition (CVD) reactor chamber in absence of the first precursor reactant source material and the second precursor reactant source material.

Chemical vapor deposition of fluorocarbon polymer thin films

Abstract: Provided are methods for forming a fluorocarbon polymer thin film on the surface of a structure. In one method, a monomer gas, preferably hexafluoropropylene oxide is exposed to a source of heat having a temperature sufficient to pyrolyze the monomer gas and produce a source of reactive CF2 species in the vicinity of the structure surface. The structure surface is maintained substantially at a temperature lower than that of the heat source to induce deposition and polymerization of the CF2 species on the structure surface. In another method a pulsed plasma is used to produce reactive CF2 species. The monomer gas pyrolysis and plasma excitation methods can be carried out individually, sequentially, or simultaneously. Flexible thin films can be produced on wires, twisted wires, neural probes, tubing, complex microstructures, substrates, microfabricated circuits, and other structures. The films have a compositional CF2 fraction of at least about 50 %, a dielectric constant of less than about 1.95, and a cross-linking density of less than about 35 %.

Synthesis and electron field emission of nanocrystalline diamond thin films grown from N2/CH4 microwave plasmas

Abstract: Nanocrystalline diamond films have been synthesized by microwave plasma enhanced chemical vapor deposition using N2/CH4 as the reactant gas without additional H2. The nanocrystalline diamond phase has been identified by x-ray diffraction and transmission electron microscopy analyses. High resolution secondary ion mass spectroscopy has been employed to measure incorporated nitrogen concentrations up to 8×1020 atoms/cm3. Electron field emission measurements give an onset field as low as 3.2 V/μm. The effect of the incorporated nitrogen on the field emission characteristics of the nanocrystalline films is discussed.

Methods for filling trenches in a semiconductor wafer

Abstract: A method for filling a trench in a semiconductor wafer that is disposed in a plasma-enhanced chemical vapor deposition chamber. The method includes the step of depositing a protection layer of silicon dioxide over the wafer and into the trench while the wafer is biased at a first RF bias level. The protection layer has a thickness that is insufficient to completely fill the trench. Further, there is provided the step of forming a trench-fill layer of silicon dioxide over the protection layer and into the trench while the wafer is biased at a second RF bias level that is higher than the first bias level.

Activated Rate Theory Treatment of Oxygen and Water Transport through Silicon Oxide/Poly(ethylene terephthalate) Composite Barrier Structures

Abstract: Poly(ethylene terephthalate) substrates were coated with thin films of silicon oxide deposited by magnetically enhanced chemical vapor deposition. The rates of oxygen and water vapor transport through the coated and uncoated film systems were obtained as a function of temperature. Activated rate theory treatment of oxygen transmission rates revealed that the silicon oxide coatings were imperfect; the apparent free energies of activation (ΔEp) for transport through film substrates which were coated on a single side were statistically identical to uncoated controls. However, coating both sides of the polymer substrate with identical oxide layers resulted in a 54 kJ/mol increase in the ΔEp value. A simple empirical model for the change in transport mechanism is offered to explain this unanticipated result. Analogous treatment of water vapor transport rates for these same film systems showed no obvious change in transport mechanism. However, ΔEp values obtained for water vapor permeation through silicon oxide...

Progress in Low‐temperature Surface Passivation of Silicon Solar Cells using Remote‐plasma Silicon Nitride

Abstract: Using a remote-plasma technique as opposed to the conventional direct-plasma technique, significant progress has been obtained at ISFH in the area of low-temperature surface passivation of p-type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma-enhanced chemical vapour deposition system. If applied to the rear surface of the low-resistivity p-type substrates, the remote-plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s−1, which is by a clear margin the lowest value ever obtained on a low-resistivity p-Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct-plasma SiN films or thermally grown oxides, the remote-plasma films not only provide significantly better SRVs on low-resistivity p-silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote-plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus-diffused emitters which is comparable to high-quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV-stable inversion-layer emitter of outstanding electronic quality. Due to the low deposition temperature and the high refraction index, these remote-plasma SiN films act as highly efficient surface-passivating antireflection coatings. Application of these films to cost-effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p-n junction cells with efficiencies above 19%, by bifacial p-n junction cells with front and rear efficiencies above 18%, by mask-free evaporated p-n junction cells with efficiencies above 18% and by MIS inversion-layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass-encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.

Optimization of a low-stress silicon nitride process for surface-micromachining applications

Abstract: A detailed examination of the effects of deposition parameters, using LPCVD, and subsequent processing on the characteristics of silicon nitride is presented The properties investigated are deposition rate, refractive index, etch rate and intrinsic strain The chemical composition of the material is determined using XPS and EPMA A close relationship between the chemical composition and mechanical properties is observed The ratio of process gas flow (using NH 3 and SiH 2 Cl 2 ) is shown to have a strong effect on all properties with deposition pressure having a secondary effect As the gas-flow ratio NH 3 /SiH 2 Cl 2 is ranged from 0176 to 1 the silicon content changes from Si/N=095 to 086, yielding a change in strain levels from 350 μϵ to 3000 μϵ Further increase in NH 3 yields only minor changes in silicon to nitrogen ratio and thus only minor changes in the film characteristics Additional thermal processing is shown to have a considerable effect on the mechanical properties of the material X-ray studies suggest that this to be due to volume shrinkage of the layer and not phase transformations involving crystallographic changes Tuning of the film properties through the processing parameters is shown

Piezoelectric thin films for mems

Abstract: A short overview is given on deposition and integration of PZT thin films on silicon for MEMS applications. The application principles are explained and the piezoelectric coefficients are compared with the ones of AlN and ZnO. The Materials figure of merits are given for various applications and discussed. The coupling coefficient for ultrasonic applications is treated in more detail.