Refractive index properties of SiN thin films and fabrication of SiN optical waveguide

SiN thin films having excellent surface morphology for the optical device application were synthesized using a plasma enhanced chemical vapor deposition (PECVD) method at low temperature (350^°C) using silane (SiH₄) and nitrogen (N₂). The effects of the SiH₄/N₂ flow ratio, rf power and annealing on the SiN films were investigated. The optical and structural properties of SiN films were characterized using an ellipsometry, a fourier-transform infrared spectroscopy (FT-IR), and an atomic force microscope (AFM). The refractive index increased from 1.6 to 2.3 as the SiH₄/N₂ ratio was increased from 0.17 to 1.67. The rms surface roughness decreased from 14.1 to 3.6Å after post-deposition annealing process performed at 800^°C for 1hr in an air ambient. We could fabricate straight waveguides based on a three layer structure and have no problems with step coverage.     

PECVD低功率沉积氮化硅薄膜研究

为了减少太阳能电池氮化硅薄膜生产工艺中的缺陷、提高太阳能电池的转换效率,采用等离子增强化学气相沉积法在射频功率较低的条件下,对N型单晶硅片表面进行氮化硅沉积,获得与高射频功率沉积时相同膜厚和折射率的氮化硅膜,通过试验分析了低功率沉积工艺对电池电参数、对膜厚均匀性的影响。结果表明,在低功率沉积工艺条件下,有助于改善膜厚均匀性,使膜厚不均匀度由12%下降到6%,太阳能电池转换效率提高了0.05个百分点。     

Atomic Mixing Behavior of Co/Al(001) vs. Al/fcc-Co(001): Molecular Dynamics Simulation

Using molecular dynamics simulations, we investigated the interface structures and the growth behaviors of nano-scale Al/Co/Al multilayers. For Co on Al(001), interface mixing occurred irrespective of the incident energy (K_i). Interestingly, increasing the incident energy increased the thickness of the mixing layers and decreased the roughness of the Co surface. In the case of Al on Co(001), in contrast to the case of Co/Al, interface mixing could not be found, especially for low incident energy. From these investigations, an optimized deposition technique is proposed that improves the quality of the interface/surface of the deposited thin film by controlling the incident adatom energies.     

Spectroscopic ellipsometric determination of optical properties of V-Al co-doped ZnO films by rf magnetron sputtering

Zn_0.9?xV_0.1Al_xO aerogel nanopowders were prepared in thin film form on glass substrates using a rf magnetron sputtering system. The films were characterized by Scanning electron microscopy (SEM) and X-ray diffraction technique (XRD). The XRD results indicate that all the films have c-axis preferred orientation due to self-texturing mechanism. The ellipsometric spectra of the films were recorded in the photon energy range of 1 eV–5 eV. The SE spectra were analyzed with an appropriate model to accurately determine the thickness and optical constants of the ZnO:(V,Al) thin films. The profiles of refractive index and extinction coefficient with photon energy were extracted. The refractive index of the ZnO:(V,Al) film is decreased from 2.14 to 2.07 with increasing Al concentration and then is increased to 2.19 for x?=?0.04. A maximum band gap energy of ~3.57 eV was obtained for x?=?0.02. The optical band gaps of the films were found to vary from 3.57 eV to 3.41 eV, with Al content. It is evaluated that the optical constants of the ZnO:(V,Al) films can be controlled by Al content.     

Low-temperature synthesis of barium titanate thin films by nanoparticles electrophoretic deposition

The nanoparticles electrophoretic deposition (EPD) of barium titanate (BaTiO₃ or BTO) thin films was investigated. BTO nanocrystallites in a pseudocubic perovskite phase with an average particle size of about 10 nm were synthesized at a low temperature of 90°C by a high-concentration sol–gel process. By using a mixed solvent of 2-methoxyethanol and acetylacetone as dispersing medium, transparent and well-dispersed BTO nanocrystallites suspensions within the concentration range of 0.0125 to 0.20 mol/l was successfully prepared for nanoparticles EPD. A uniform microstructure and a smooth surface were observed on the deposited films. The film thickness of the deposited films increased rapidly with increasing EPD time in the initial period of EPD, and thereafter gradually increased to a limited thickness. With increasing applied EPD voltage, the limited film thickness increased. A near linear relation between the film thickness of films and the concentration of suspensions was observed under the same EPD conditions. The microstructures of the deposited BTO thin films were investigated.     

PREPARATION OF BaTiO3 FILMS FOR MLCCS BY DIRECT VAPOR DEPOSITION

ABSTRACT

BaTiO₃ films were deposited by the direct vapor deposition (DVD) technique to prepare thin dielectric layers for multilayer ceramic chip capacitors (MLCCs). The BaTiO₃ films were successfully prepared by co-evaporation of the BaTiO₃ ceramic and Ti metal source. The films deposited at room temperature and 600°C were amorphous and crystalline phases, respectively. The intensity of (110) and (111) peaks increased as Ba/Ti ratios were close to stoichiometric composition. BaTiO₃ films deposited with e-beam power of 700 W showed the deposition rate of 33 nm/min. The dielectric constant and dissipation factor of BaTiO₃ films measured at 1 kHz were 150～ 180 and 2～ 5%, respectively. The capacitance decreased with increasing the temperature and varied only between 787pF and 752pF in the temperature range 15～ 125°C.     

Growth and electrical properties of Pb(Zr,Ti)O3 thin films by sputtering using an alloy target

Abstract

Pb(Zr_x,Ti_1?x)O₃ thin films were deposited on Pt/SiO₂/Si substrates by the rf magnetron sputtering using an alloy target consisting of Zr-Ti alloy and Pb metal. The dependence of electrical properties on film thickness and sputtering gas pressure was investigated. The dielectric constant and the remanent polarization decreased and the coercive field increased with the decrease of the film thickness. In the dependence of gas pressure, the relative dielectric constant of the film with only a perovskite phase were in the range of 235–280, which were higher than those of the film with only a pyrochlore phase, 20. The asymmetry of hysteresis loops increased with the decrease of the gas pressure.     

Doping level-dependent dry-etch damage in n-type GaN

The electrical effects of dry-etch on n-type GaN by an inductively coupled Cl₂/CH₄/H₂/Ar plasma were investigated as a function of ion energy, by means of ohmic and Schottky metallization methods. The specific contact resistivity (ρ_c) of the ohmic contact was decreased, while the leakage current in the Schottky diode was increased with increasing ion energy due to the preferential sputtering of nitrogen. At a higher rf power, an additional effect of damage was found on the etched sample, which was sensitive to dopant concentration in terms of the ρ_c of the ohmic contact. This can be attributed to effects such as the formation of deep acceptors as well as the electron-enriched surface layer within the depletion layer. Furthermore, the thermal annealing process enhanced the ohmic and Schottky properties of the heavily damaged surface.     

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.     

Double antireflection coating layer with silicon nitride and silicon oxide for crystalline silicon solar cell

Anti-reflection coating (ARC) film effectively reduces the reflection of sunlight on the silicon wafer surface and then increases substantially the solar cell conversion efficiency. In this work, we carried out experiments to lessen the reflectance and thus improve the conversion efficiency with double AR coating layer with silicon nitride and silicon oxide by plasma enhanced chemical vapor deposition (PECVD) for the silicon solar cells. The optimized thicknesses and refractive indices of each ARC layer were calculated with Essential Macleod program and the theoretical method. The single antireflection layer of silicon nitride was applied with 800 Å thickness and its cell showed the conversion efficiency as 17.45 %. For the double layer AR coating (DLARC), silicon nitride layer was deposited first using SiH₄ and NH₃, and then, silicon oxide was deposited with SiH₄ and N₂O. The thicknesses of SiN_x and SiO₂ were 800 Å and 1400 Å for DLARC-1 and 500 Å and 1000 Å for DLARC-2, respectively. As a result, the reflectance of DLARCs was lower than single SiN_x and then yielded increase of short-circuit current and conversion efficiency. The completed solar cell with DLARCs showed conversion efficiencies of 17.57 % for DLARC-1 and 17.76 % for DLARC-2. This indicates that the double AR coating layer is effective to obtain the high efficiency solar cell with PECVD.     

Optical properties of RF-sputtered Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ?=?650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.     

Effects of the Ga-doping concentration on the characteristics of Zn<Subscript>0.7</Subscript>Mg<Subscript>0.3</Subscript>O thin films deposited by metal-organic chemical vapor deposition using an ultrasonic nebulization

Ga-doped Zn_0.7-xMg_0.3O thin films were deposited on glass substrates at 350 °C by metal-organic chemical vapor deposition using an ultrasonic nebulization technique to transport the source precursors, and the effects of the Ga-doping concentration were investigated. The films with Ga-doping concentrations less than 5 mol% grew with [001] preferred orientation perpendicular to the substrate surface and were composed of large crystallites. At Ga content greater than 5 mol%, the films grew with random orientation and very small crystallite size. The charge carrier concentration in the films increased rapidly up to 4 mol% Ga and then decreased gradually with further increases in the Ga-content. The film resistivity decreased with increasing Ga-content up to 4 mol% due mainly to the increase in charge carrier concentration. Then, the resistivity increased gradually with increasing Ga-content due to the decrease in mobility. The lowest resistivity of the Ga-doped Zn_0.7-xMg_0.3O thin film was 3.8?×?10^?1 Ωcm at the Ga doping concentration of 4 mol%. The mean transmittance in the visible range was more than 85% in all films. The optical band gap of the films increased with increasing Ga-doping concentration up to 5 mol% due to the Burstein-Moss effect.     

CHARACTERIZATIONS OF W-DOPED (Ba0.5Sr0.5)TiO3 THIN FILMS USING LaNiO3 ELECTRODE

ABSTRACT

The (Ba_0.5Sr_0.5)TiO₃ thin films were deposited onto LaNiO₃ by RF-magnetron sputtering at 550°C. The influence of W content on microstructure and electrical properties of BST films were investigated. The surface and grain size become smoother and smaller as the W content increased. Besides, the dielectric constant, tunability, dissipation factor, and leakage current decreased when the W content increased. The 1% W is the optimal doping concentration. The resultant BST film, with proper dielectric constant and leakage current, has a tunability of 32%, a dissipation factor of 0.006, a FOM value of 53.3 under applied field of 450 kV/cm.     

Liquid source chemical vapor deposition of high-dielectric-constant (Ba,Sr)TiO3 films

High-dielectric-constant (Ba, Sr)TiO₃ [BST] films were deposited by the liquid source chemical vapor deposition (CVD) method. The system consisted of a single-wafer, low-pressure thermal CVD reactor, a vaporizer for liquid source materials, and a shower-type gas nozzle head, giving stable BST film deposition on a 6-in. diam. substrate with uniform thickness and uniform chemical composition ratio. The source materials employed were Ba(DPM)₂, Sr(DPM)₂, and TiO(DPM)₂ dissolved in tetrahydrofuran (THF), resulting in conformal step coverage of BST films at lowered substrate temperatures, where DPM denotes dipivaloylmethanate. Moreover, the two-step deposition technique was developed to restart protrusions formed on BST film surfaces at low temperatures, where the BST films consisted of a buffer layer and a main layer; the buffer layer was a layer about 60 Å thick of CVD-BST film annealed in N₂. Thus, the two-step CVD deposition of BST films on Pt and Ru electrodes achieved an equivalent SiO₂ thickness of t_eq ∼ 0.5 nm, a leakage current of J_L ∼ 1.0 × 10⁻⁸ A/cm² (at +1.1 V), and a dielectric loss of tan δ ∼ 0.01 at a total film thickness of 250 Å, along with conformal coverage of 80% for a trench with an aspect ratio of 0.65. Then, for BST films deposited on patterned electrodes 0.24 μm wide, 0.60 μm deep, and 0.15 μm high (each spaced by 0.14 μm), the capacitance was demonstrated to be increased without significant deterioration of the leakage current: the capacitance was increased in comparison with that for films on flat electrodes, by a factor corresponding to the increase in surface area due to sidewalls of storage-node-like pattern features. This capacitance increase reflects the most characteristic advantage of CVD, an excellent step coverage on microscopic pattern features. These electrical properties satisfy the specifications for capacitors for Gb-scale dynamic random access memories (DRAMs), giving a storage capacitance of more than 25 fF/cell for a stacked capacitor having a storage node 0.2 to 0.3 μm high. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 47–54, 1998     

Relation between breakdown voltage and prebreakdown current in vacuum gap

Two different surface treatments (mechanical polishing, thin film deposition) were performed on cathode surfaces, and the field emission currents from the cathodes were measured with a microchannel plate. In order to discuss the relationship between the breakdown voltage and prebreakdown current in the vacuum gap, the breakdown voltage was measured after field emission measurement. The V–I characteristics of the field emission and breakdown voltage were influenced by surface treatment, and the breakdown voltages of mechanical polished cathodes were lower than those of the thin film deposited cathodes. It was found that the probability of breakdown increased when the field emission current reached 10^–11 A. Atomic force microscope (AFM) measurements showed numerous protrusions on the cathode surface in the case of thin film deposition treatment, but we estimated by the finite element method that these protrusions make the field enhancement effect low. It was inferred that the breakdown voltage in vacuum gaps could be increased by the thin film deposition method. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 11–18, 2000     

Influence of the growth temperature on the epitaxial quality of PbTiO3 films deposited in-situ by sputtering

Abstract

Thin films of lead titanate were prepared in-situ on SrTiO₃ substrates using radio-frequency magnetron sputter deposition. The epitaxial quality of the films has been studied as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range [550°C, 600°C]. The films deposited in the equilibrium zone have a high degree of c-axis oriented epitaxial crystalline structure as shown by X-ray diffraction in the 2θ/θ, θ, and ? scans configuration as well as by electron channeling pattern. The optimum conditions for growing epitaxial PbTiO₃ layers were determined. The crystallinity of films deposited at 550°C is suprior to those deposited at 600°C. The PbTiO₃ films grown at 550°C have a rocking curve full width at half maximum (FWHM) of 0.2°; Normaski optical and atomic force microscopy show that the surface is apparently free of grain boundaries and very smooth. The refractive index of these films has been evaluated from transmission spectra; it is very close to the bulk material value.     

Chemical Vapor Deposition of Ru Bottom Electrode for Ferroelectric Bi4 − x La x Ti3O12 Capacitors

Ruthenium films formed by metalorganic chemical vapor deposition were investigated, taking account of the application to the bottom electrode of ferroelectric capacitors. Ruthenium films were deposited using a liquid-type source of Ru[EtCp]₂ in a cold-wall type reactor with infrared lamps. A smooth and flat Ru film was successfully formed on a SiO₂-covered Si substrate without a seed layer. As the deposition temperature increased to 400°C, the crystallinity of the Ru film improved and the film exhibited high c-axis orientation. After forming a Bi_{4 ? x} La _x Ti₃O₁₂ (BLT) film by a sol-gel technique, a Pt/BLT/Ru capacitor was fabricated on the Ru film. Good hysteresis loops with 2P _r = 20 μC/cm² and 2V _c = 3.4 V were successfully obtained and the ferroelectric property did not depend on the deposition temperature of Ru in the temperature range from 325°C to 400°C. On the contrary, the leakage current density was significantly suppressed down to 1/100 as the deposition temperature of Ru increased from 325°C to 400°C.     

Phase formations and ferroelectric properties of PLT thin films by MOCVD

Abstract

La-modified lead titanate, Pb_1-x La _x TiO₃(PLT), thin films were prepared on Si[100] and Pt/SiO₂/Si substrates by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method with the hot-wall type. The PLT films were deposited at 500°C with the low-pressure of 0.1 Torr, and then annealed at 650°C with an oxygen ambient for 10 minutes. Irrespective of substrate properties and La molar fractions, the films revealed the [100] preferred-orientation. With increasing the La mole %(up to 34%) in the films, the surface morphology improved, and the ferroelectricity and the leakage current density decreased. On the other hand, up to the La 22 mole%, the relative dielectric constant increased from 900 to 1200.     

Asymmetrical single-mode silica waveguide deposited by PECVD

Silicon oxynitride (SiON) layer and SiO₂ buffer layer were deposited on silicon wafers by PECVD technique using SiH₄, N₂O and N₂. The refractive index of SiON films measured at a wavelength of 1552 nm using a prism coupler, could be continuously varied from 1.4480 to 1.4508. Optical planar waveguides with a thickness of 6 μm and a refractive index contrast (Δn) of 0.36% have been obtained. In addition, etching experiments were performed using ICP dry etching equipment on thick SiON films grown on Si substrates covered with a thick SiO₂ buffer layer. In order to measure optical properties, a polarization maintaining single-mode fiber was used for the input and a microscope objective for the output at 1.55 μ m. A low-loss and low propagation SiON-based waveguide was fabricated with easily adjustable refractive index of core layer.     

Improvement of heating characteristics of molybdenum silicide thin film electric heaters

Molybdenum silicide (MoSi₂) has an electrical conductivity as high as that of a metal, and greater chemical stability than that of, for example, SiC, in various atmospheres. Therefore, many kinds of MoSi₂ bulk‐type heaters are used in practical operations up to 1800^°C, which is higher than the temperature of SiC heaters. However, MoSi₂ is fragile at room temperature and has low creep resistance at high temperature. The purpose of this study is to fabricate heaters using thin films of MoSi₂ deposited on alumina substrates and crucibles by RF magnetron sputtering and to evaluate their characteristics. MoSi₂ thin film was deposited on the outside of an alumina crucible without heating the substrate and then Pt wire was attached using a Pt paste with sintering in a vacuum. This MoSi₂ thin film heater showed almost linear resistance–temperature (R–T) characteristics and a uniform heating state. It also showed good controllability of voltage and stability in the power–T characteristics for operations up to 1000^°C. However, at a heating temperature of 1300^°C, the heating area of MoSi₂ thin film decreased because of the reaction between Pt and MoSi₂ in the case of long‐term heating. Thus, Mo thin film was deposited as a buffer layer between Pt and MoSi₂ thin film to prevent such a reaction. This thin film heater showed good linear R–T characteristics up to 1200^°C. However, the temperature coefficient of resistance changed with repeated heating operation as a result of the diffusion of Mo atoms into MoSi₂. Thus, a thin film heater was fabricated with Mo₃Si, having a higher Mo content than MoSi₂. This heater showed a low degree of diffusion of Mo or Pt atoms into the thin film and had excellent practical characteristics up to 1000^°C. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(2): 11–19, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20806