Showing papers on "Silicon published in 1988"

Empirical interatomic potential for silicon with improved elastic properties.

Abstract: An alternative parametrization is given for a previous empirical interatomic potential for silicon. The new potential is designed to more accurately reproduce the elastic properties of silicon, which were poorly described in the earlier potential. The properties of liquid Si are also improved, but energies of surfaces are less accurate. Detailed tests of the new potential are described.

Bonding of silicon wafers for silicon‐on‐insulator

Abstract: Several aspects of a new silicon‐on‐insulator technique utilizing bonding of oxidized silicon wafers were investigated. The bonding was achieved by heating in an inert atmosphere a pair of wafers with hydrophilic surfaces contacted face‐to‐face. A quantitative method for the evaluation of the surface energy of the bond based on crack propagation theory was developed. The bond strength was found to increase with the bonding temperature from about 60–85 erg/cm2 at room temperature to ≂2200 erg/cm2 at 1400 °C. The strength was essentially independent of the bond time. Bonds created during 10‐s annealing at 800 °C were mechanically strong enough to withstand the mechanical and/or chemical thinning of the top wafer to the desired thickness and subsequent device processing. A model was proposed to explain three distinct phases of bonding in the temperature domain. Electrical properties of the bond were tested using metal‐oxide‐semiconductor (MOS) capacitors. The results were consistent with a negative charge de...

Silicon carbide semiconductor device

Abstract: PURPOSE: To prevent leakage currents even under severe conditions such as a high temperature, large power, etc., by forming a first electrode onto the surface of an silicon carbide semiconductor layer shaped onto one surface of a substrate, a second electrode onto the other surface of the substrate and a third electrode onto the side face of the silicon carbide semiconductor layer. CONSTITUTION: A nickel film formed onto the rear of an silicon substrate 1 is used as a drain electrode 7, and a titanium-aluminum film shaped onto the projecting end face of an silicon carbide growth layer 2 having mesa structure is employed as a source electrode 6. Currents flowing between the source electrode 6 and the drain electrode 7 are controlled by fluctuating voltage applied to gate electrodes 8 and changing the width of depletion layers 9 spreading in the silicon carbide growth layer 2. Accordingly, an silicon carbide semiconductor device, in which leakage currents are not generated even under severe conditions such as a high temperature, large power, etc., and which has excellent characteristics, can be acquired. COPYRIGHT: (C)1989,JPO&Japio

The formation of hydrogen passivated silicon single‐crystal surfaces using ultraviolet cleaning and HF etching

Abstract: We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin‐film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high‐purity level by scanning electron microscopy, reflection high‐energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.

A model for the discharge kinetics and plasma chemistry during plasma enhanced chemical vapor deposition of amorphous silicon

Abstract: A model for the plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon (a‐Si:H) in rf and dc discharges is presented. The model deals primarily with the plasma chemistry of discharges sustained in gas mixtures containing silane (SiH4). The plasma chemistry model uses as input the electron impact rate coefficients generated in a separate simulation for the electron kinetics and therefore makes no a priori assumptions as to the manner of power deposition. Radical densities and contributions to film growth are discussed as a function of gas mixture, electrode separation, and locale of power deposition, and comparisons are made to experiment. A compendium of reactions and rate constants for silane neutral and ion chemistry is also presented.

Amorphization and conductivity of silicon and germanium induced by indentation.

Abstract: We report the observation, by transmission electron microscopy, that single-crystal silicon and germanium are converted to an amorphous state at room temperature directly under both Vickers and Knoop indentations. The effect is seen for crystal orientations of [001], [011], and [111], and with applied loads between 0.1 and 0.5 N. We also observe that the materials become electrically conducting under load and that the process is reversible on subsequent unloading and reloading. Furthermore, the transformed phase is found to make Ohmic contact to the surrounding, untransformed, semiconductor.

Bonding and stabilities of small silicon clusters: A theoretical study of Si7–Si10

Abstract: Ab initio calculations have been performed to study the structures and energies of intermediate‐sized silicon clusters (Sin, n=7–10). All geometries have been optimized at the Hartree–Fock (HF) level of theory with the polarized 6‐31G* basis set. The harmonic vibrational frequencies have been evaluated at the HF/6‐31G* level of theory. Electron correlation effects have been included by means of fourth order Mo/ller–Plesset perturbation theory. The most stable structure for Si7 is a pentagonal bipyramid and the lowest energy calculated structures for Si8–Si10 correspond to capped octahedral or prismatic geometrical arrangements. The evolution of the cluster geometries with increasing size is discussed. Clusters containing four, six, seven, and ten atoms have been identified as ‘‘magic numbers’’ for small silicon clusters, both theoretically and experimentally. The hybridization and bonding in small silicon clusters is discussed. Our results are used to interpret the recent photoelectron spectra of negative...

Large grain polycrystalline silicon by low‐temperature annealing of low‐pressure chemical vapor deposited amorphous silicon films

Abstract: The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.

Experimental determination of the nanocrystalline volume fraction in silicon thin films from Raman spectroscopy

Abstract: The effect of crystallite sizes L smaller than 100 nm on the integrated Raman cross section Σc of the transverse optical (TO) mode of fcc silicon was studied experimentally in fully nanocrystallized thin films. The Σc/Σa (amorphous) ratio of this mode is shown to be 1 up to L=30 A, and to decay exponentially down to 0.1 at larger L. A systematic procedure taking into account both this effect and the experimental optical absorption coefficient αexp at the excitation wavelength is then proposed for the determination of the crystalline volume fraction in mixed phase (amorphous/nanocrystalline) silicon systems by Raman measurements.

Thermally excited silicon microactuators

Abstract: A cantilever-type micromachined silicon actuator based on the bimetal effect used extensively for the fabrication of temperature-controlled electrical switches is described. The silicon actuator consists of a Si-metal sandwich layer and an integrated poly-Si heating resistor as a driving element. Due to the low heat capacity of the transducer element, a high temperature increase per input power unit can be achieved. For a (Si-Au)-cantilever-type actuator, 500- mu m long and several micrometers thick, a specific deflection of approximately 0.1 mu m/K at the free end has been measured. The design considerations, fabrication process, and experimental results of the actuator are discussed. >

Structural, dynamical, and electronic properties of amorphous silicon: An ab initio molecular dynamics study.

Abstract: An amorphous silicon structure is obtained with a computer simulation based on a new moleculardynamics technique in which the interatomic potential is derived from a parameter-free quantum-mechanical method. Our results for the atomic structure, the phonon spectrum, and the electronic properties are in excellent agreement with experiment. In addition we study details of the microscopic dynamics which are not directly accessibly to experiment. We find in particular that structural defects are associated with weak bonds. These may give rise to low-frequency vibrational modes.

Silica-based single-mode waveguides on silicon and their application to guided-wave optical interferometers

Abstract: Low-loss silica-based single-mode waveguides and directional couplers are fabricated on silicon substrates. Their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated. Optical switches or tunable optical couplers are fabricated using the thermooptic effect. Asymmetrical Mach-Zehnder interferometers are successfully applied to multi/demultiplexers for optical FDM transmission systems. >

NMR confirmation of strained “defects” in amorphous silica

Abstract: Solid state 29 Si magic angle sample spinning nuclear magnetic resonance spectroscopy and Raman spectroscopy were used to investigate the local silicon environment and siloxane ring vibrations in amorphous silica gels. Our results unambiguously relate the 608 cm −1 Raman “defect” in a-SiO 2 with reduced SiOSi bond angles indicative of strained 3-membered rings of silicate tetrahedra.

The physics and technology of amorphous SiO[2]

Abstract: Structure: Theory and Experiment.- Current Models for Amorphous SiO2.- Structural Similarities and Dissimilarities Between SiO2 and H2O.- Geometrical Methods in the Theory of Glasses.- Low Lying Excitations in Silica.- New Methods of IR Spectroscopic Investigation of Amorphous Insulating Films.- Vibrational Studies of Amorphous SiO2.- Raman Spectra of SiO2 Fibers at High Tensile Strain.- A Comparison of the Structure of a-SiO2 Prepared by Different Routes.- NMR Studies of Neutron-Irradiated Crystalline and Vitreous SiO2.- Intrinsic and Extrinsic Defects: Theory.- Electronic Structure of Defects in Amorphous SiO2.- Electron and Hole Traps Related to ? Bonded Oxygen Vacancy Centers in SiO2.- Theory of Oxygen-Vacancy Defects in Silicon Dioxide.- Total Energy Calculations for Intrinsic Defects in Amorphous SiO2.- Boron Impurity Centers in Si02: a Tight Binding Consideration.- Intrinsic and Extrinsic Defects: Experiment.- Intrinsic and Extrinsic Point Defects in a-SiO2.- Self-Trapped Excitons in Amorphous and Crystalline SiO2.- Identification of Native Defects in a-SiO2.- UV and VUV Optical Absorption due to Intrinsic and Laser Induced Defects in Synthetic Silica Fibers.- Incommensurate Phase of Quartz: Microscopic Origin and Interaction with Defects.- Gamma Ray Induced 2 eV Optical Absorption Band in Pure Silica Core Fibers.- On the Decay of X-Ray Induced Luminescence of SiO2.- On the Role of O-2 in the Luminescence of Amorphous and Crystalline SiO2.- Transformation of Radiation Induced Defect Centers as a Probe of Molecular Diffusion in a-SiO2.- Observation of the Neutral Oxygen Vacancy in Silicon Dioxide.- New Insight Into the Structure of SiO2 Glass from a Point Defect Study.- Hydrogen Bonds Between Peroxy Radicals and Hydrogen Molecules in SiO2 Glass.- ESR Studies of111< Si/SiO2 Interface.- Structure and Hyperfine Interaction of Si ? Si* Defect Clusters.- On the Relationship Between Thermal Growth and Thickness Inhomogeneities in Very Thin SiO2 Films.- The Pb Center at the Si-SiO2 Precipitate Interfaces in Buried Oxide Materials: 29Si Hyperfine Interactions and Linewidths.- Metastable and Multiply-Charged Individual Defects at the Si:SiO2 Interface.- The Influence of Disorder on the Si2p XPS Lineshape at the Si-SiO2 Interface.- Si-SiO2 Interfaces - a HRTEM Study.- Electrical and Interface Properties of MOS Structures of Getter Treated Silicon.- Influence of Different Preparation Methods on Interfacial (Si/SiO2) Parameters of Very Thin Layers.- Oxidation, Oxynitrides And Deposited Films.- Thermal Oxidation of Silicon.- A Framework for Incorporating Memory Effects of Structural Relaxation in Models for Thermal Oxidation of Silicon.- Analysis of Stress Relaxation and Growth Kinetics for Two-Step Thermal Oxidation of Silicon.- Photo-Induced Oxidation Processes in Silicon.- Growth and Structure of Argon Laser Grown SiO2.- Transport Properties of Plasma Enhanced CVD Silicon Oxynitride Films.- Characteristics of SiO2 and SiOxNy Obtained by Rapid Thermal Processes.- Evidence for Oxygen Bubbles in Fluorine Doped Amorphous Silicon Dioxide Thin Films.- Low Temperature PECVD Silicon Rich Silicon Dioxide Films Doped With Fluorine.- Transport, Trapping and Breakdown.- High Field Transport in SiO2.- Hot Electrons in SiO2: Ballistic and Steady State Transport.- Electronic Charge Transport in Thin SiO2 Films.- The Role of Hole Traps in the Degradation of Thermally Grown SiO2 Layers.- The Influence of Temperature Nitrogen Annealing on the Electrical Properties of Plasma Nitrided Oxides.- High-Field Positive-Charge Generation and Its Relation to Breakdown in a-SiO2.- Breakdown Mechanisms of Thermally Grown Silicon Dioxide at High Electric Fields.- Field Dependence of Time to Breakdown Distribution of Thin Oxides.- Radiation Effects.- Radiation Effects in MOS VLSI Structures.- Relationship Between Hole Trapping and Interface State Generation in the Si/SiO2 System.- Radiation Induced Conductivity of Thin Silicon Dioxide Films on Silicon.- Interface Degradation in Short Channel MOSFETs: Comparison Between the Effects of Radiation and Hot Carrier Injection.- Buried Dielectric Layers and Novel Applications.- Synthesis of Buried Dielectric Layers in Silica by Ion Implantation.- Electrical Properties of SIMOX Material and Device.- Formation Mechanisms and Structures of Thin Buried Layers of SiO2 Fabricated Using Ion Beam Synthesis.- Low Temperature ESR Study of SIMOX Structures.- Defects in Silicon-on-Insulator Structures Formed by O+ Implantation: Their Dependence on Implantation Temperature.- Interface Properties and Recombination Mechanisms in SIMOX Structures.- Porous Silica Sol-Gel Coatings for Nd: Glass High Power Pulsed Laser Laser Uses.- Vacuum Re-Emission of Positrons from a-SiO2 Layers.- Author Index.

Thermal and stress analysis of semiconductor wafers in a rapid thermal processing oven

Abstract: Results are presented from studies of heat transfer in a rapid thermal processing (RTP)-type oven used for several semiconductor wafer processes. These processes include: (1) rapid thermal annealing; (2) thermal gradient zone melting; and (3) lateral epitaxial growth over oxide. The heat transfer studies include the measurement of convective heat transfer in a similar apparatus, and the development of a numerical model that incorporates radiative and convective heat transfer. Thermal stresses that are induced in silicon wafers are calculated and compared to the yield stress of silicon at the appropriate temperature and strain rate. Some methods for improving the temperature uniformity and reducing thermal stresses in the wafers are discussed. >

Method of fabricating back surface point contact solar cells

Abstract: A back surface point contact silicon solar cell having improved characteristics is fabricated by hydrogenating a silicon-silicon oxide interface where hydrogen atoms are diffused through silicon nitride and silicon oxide passivating layers on the surface of a silicon substrate. In carrying out the hydrogenation, the substrate and passivation layers are placed in a hydrogen atomsphere at an elevated temperature of at least 900° C. whereby hydrogen atoms diffuse through the two passivation layers. Self-alignment techniques are employed in forming small-geometry doped regions in the surface of the silicon substrate for the p-n junctions of the solar cell. Openings are formed through the passivation layers to expose first surface areas on the substrate, and a doped silicon oxide layer is then formed over the passivation layers and on the exposed surface areas. Portions of the first doped layer on the two passivation layers are removed and then second portions of the two passivation layers are removed, thereby exposing second surface areas. A second doped silicon oxide layer is then formed over the passivation layers and on the second exposed surface areas. Dopants from the two doped silicon oxide layers are then diffused into the first and second surface layers to form p and n diffused regions in the surface of the substrate. Thereafter, the first and second doped silicon oxide layers are removed by a preferential etchant which does not remove the silicon nitride layer, thereby exposing the first and second surface areas. A two-level metal interconnect structure is then formed for separately contacting the first surface areas and the second surface areas.

Production of high-quality amorphous silicon films by evaporative silane surface decomposition

Abstract: High‐quality hydrogenated amorphous silicon films (a‐Si:H) have been produced by decomposition of low‐pressure silane gas on a very hot surface with deposition on a nearby, typically 210 °C substrate. A high‐temperature tungsten filament provides the surface for heterogeneous thermal decomposition of the low‐pressure silane and subsequent evaporation of atomic silicon and hydrogen. These evaporated species (primarily) induce a‐Si:H growth on nearby substrates which are temperature controlled using a novel substrate holder. The light and dark conductivities, optical band gap, deposition rates, and light‐soaking effects of preliminary films are reported. The decomposition‐evaporation process has been examined using a mass spectrometer to directly detect the decomposition rate and the evaporated radical species. Based on this data and other information, a simplified model for the deposition process is suggested. The excellent film quality and the attributes of the deposition process make this technique, which was originally suggested by Wiessman, viable for the fast rate, large‐area deposition of a‐Si:H for solar cells and other applications.

Wettability and Work of Adhesion of Nonreactive Liquid Metals on Silica

Abstract: Wettability of silica by gold, silicon, and lead has been determined by the sessile-drop method. The contact angle, θ, and the work of adhesion, W, have been found to be 143° and 227 mJ·m−2 for gold at 1353 K, 87° and 869 mJ·m−2 for silicon at 1723 K, and 120° and 203 mJ·m−2 for lead at 1000 K. Thermodynamic adhesion between silica and nonreactive pure metals has been analyzed using models for metal-oxide bonds. Models based on the assumption that only van der Waals interactions and/or metal-oxygen chemical bonds exist at the metal-oxide interface are unsuited for explaining the relative variations in the W values. A valid model can be accomplished by using an empirical equation which takes into account both metal-oxygen and metal-oxide chemical bonds. It appears that chemical bonds exist at the interface even for nonreactive metal-ionocovalent oxide systems.

Electrically active point defects in amorphous silicon nitride: An illumination and charge injection study

Abstract: We observe a strong correlation between changes in the density of paramagnetic silicon ‘‘dangling‐bond’’ centers and changes in the space‐charge density in amorphous silicon nitride films subjected alternately to illumination and both positive‐ and negative‐charge injection. We demonstrate that ultraviolet illumination annihilates space charge and creates stable paramagnetic centers in silicon nitride. These centers can be passivated with a 1‐h anneal at 250 °C. Our results provide the first direct experimental evidence associating a specific point defect with the trapping phenomena in amorphous silicon nitride. We also demonstrate both directly and for the first time the amphoteric nature of the silicon nitride dangling‐bond center. Furthermore, our ability to cycle the defect between its paramagnetic neutral state and both its charged diamagnetic states suggests that the optical generation of dangling bonds in amorphous silicon nitride involves no complex structural rearrangement, but simply changes in ...

Raman scattering studies of chemical-vapor-deposited cubic SiC films of (100) Si

Abstract: Raman scattering studies for a series of CVD-grown cubic SiC single-crystal films with film thickness from 600 A to 17 microns are discussed. The results suggest that the crystalline orientations of the Si substrate and the 3C-SiC film are the same. It is found that the Si 522/cm phonon from a Si wafer is enhanced in intensity by a factor of 2-3 due to a CVD overlayer of cubic SiC, and that the 3C-SiC longitudinal optical phonon at the Gamma point from SiC/Si samples is enhanced by a factor of two or three following the removal of the Si substrate. The variation of the Raman spectrum with incident power is investigated, and a method for determining the Raman cross section for 3 C-SiC is proposed.

Method for etching silicon nitride

Abstract: A process for etching silicon nitride which utilizes free radicals from a remote plasma generated using a fluorine containing gas; and hydrogen; to produce an etch which is selective to selected materials, for example, silicon and silicon dioxide.

Microstructure and the light‐induced metastability in hydrogenated amorphous silicon

Abstract: Using a parameter obtained from infrared measurements of the silicon‐hydrogen stretch mode, the amout of light‐induced degradation in hydrogenated amorphous silicon (a‐Si:H) has been explored as a function of the amount of microstructure present in our samples. We find that samples with more microstructure, and also more bonded hydrogen, show an increased light‐induced effect. At the same time, the volume density of states in the initial (annealed) state remains virtually unchanged. We discuss how the present results relate to existing models proposed to describe the light‐induced effect.

Transient boron diffusion in ion-implanted crystalline and amorphous silicon

Abstract: Boron diffusion in ion‐implanted and annealed single‐crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1×1015 and 3×1015cm−2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distance. The samples were annealed by furnace or rapid thermal annealing to 900–1100 °C with or without a preanneal at 600 °C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single‐crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profi...