Showing papers on "Silicon published in 1972"

Dislocation Etch for (100) Planes in Silicon

Abstract: A new etch composed of a dilute aqueous solution of an alkali dichromate and hydrofluoric acid, for suitably revealing dislocations and other lattice defects in (100) planes of silicon, is reported. The etch is fast (typically 5 min), brings out both lineage (low angle grain boundaries) and slip lines, and works over a wide range of resistivities for n‐ and p‐type material. The application of the etch is not restricted to (100) planes; dislocation etch pits are formed on all crystallographic orientations. The same etching characteristics were found with dilute aqueous solutions prepared from various chromium compounds and hydrofluoric acid.

Study of the Homology between Silicon and Germanium by Thermal-Neutron Spectrometry

Abstract: The phonon dispersion relations in silicon and germanium are found to be nearly homologous with small but significant deviations. These results, which have been obtained by thermal-neutron spectrometry, are strongly supported by an analysis in which comparison is made with elastic constants, heat capacities, and Raman frequencies for these elements. Previously observed discrepancies between results obtained from shell-model calculations and from heat-capacity measurements are explained. Attempts are made to elucidate the origin of the observed differences between the dimensionless phonon frequencies of group-IV $B$ elements with the diamond-type crystal structure.

Formation of silicon oxide over gold layers on silicon substrates

Abstract: When a single‐crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100–300°C) in an oxidizing atmosphere, a silicon‐dioxide layer is readily formed over the gold layer. The mechanism and factors controlling this low‐temperature oxide formation have been investigated using backscattering of 2‐MeV He+ ions. The oxide layer is nonuniform in thickness and the initial growth of this layer is proportional to (time)1/2. Both oxidizing ambient and orientation of the substrate influence the growth rate, and the amount of gold determines the final thickness of oxide. A model is proposed to explain the oxide‐growth mechanism.

Etch Channel Formation during Anodic Dissolution of N‐Type Silicon in Aqueous Hydrofluoric Acid

Abstract: Anodic dissolution of n+‐, n‐, and n−‐type silicon in 5% aqueous hydrofluoric acid at moderate current densities results in the formation of etch channels which propagate in crystal‐oriented directions in the monocrystal. Density and depth of the channels are a function of the applied voltage, the donor concentration, and the exposure time of the electrolyte under anodic bias conditions. It is assumed that the channel formation originates at spots with a lower breakdown voltage of the depletion layer which exists on the surface of the crystal under reverse bias conditions. Channel formation in epitaxial n layers can occur during preferential electrochemical etching of the n+ substrate of structures. This is the case when the interface profile is not abrupt and when defects in the epitaxial layer are present. Some methods of restricting the influence of channels occurring during device processing are mentioned.

Growth Kinetics Observed in the Formation of Metal Silicides on Silicon

Abstract: Backscattering of MeV He ions has been used to investigate the composition and growth kinetics of metal silicides formed from thin films of Pd, Ti, Cr, and Mo evaporated onto Si. In each system studied, one silicide phase predominated (Pd2Si, TiSi2, CrSi2, and MoSi2). The thickness of the phase increased with (time)0.5 for Pd2Si and TiSi2, and linearly in time for CrSi2 and MoSi2. It was found that these two time dependencies correlate directly with the reaction sensitivity to a thin oxide interface (<100 A) and to the extent of the silicide formation in the neighborhood of a typical device contact region.

The Effect of HCl and Cl2 on the Thermal Oxidation of Silicon

Abstract: The addition of a few mole per cent of or to the oxidizing atmosphere has been found to significantly improve the electrical stability of dry‐grown films. The results reported here were obtained with 30 min oxidation at 1150°C. The process not only decreases the mobile ion contamination originating from the furnace tube, but to a large extent also passivates the films against ionic instabilities caused by contaminated metallization. The use of or apparently also reduces the number of surface states at the interface. No significant change between standard and or oxides was observed in oxide charge, dielectric strength, dielectric constant and index of refraction, but the oxidation rate of Si is considerably increased in the presence of or . The mixture of and dry was also found to be very effective for the "cleaning" of quartz furnace tubes.

Formation of Amorphous Silicon by Ion Bombardment as a Function of Ion, Temperature, and Dose

Abstract: The dose (fluence) of 200‐keV boron, phosphorous, and antimony ions required to produce a continuous amorphous layer in silicon is determined as a function of target temperature. EPR measurements are used to monitor the process which is also then related to annealing effectiveness. The continuous amorphous layer recrystallizes at 550°C, after which only the implanted ions within that layer are completely electrically active. Carrier concentration profiles indicate the position of the amorphous layer and allow an approximate determination of the distribution with depth of damage. At the low dose rates used, reasonable agreement with a simple model for the formation of amorphous silicon as a function of ion, temperature, and dose is obtained.

Technique for determining concentration profiles of boron impurities in substrates

Abstract: A new technique is described in detail which can be used to profile boron impurities in almost any substrate to a depth of a few microns. It uses the reaction 10B (n,4He)7Li to convert boron atoms to monoenergetic α particles which are detected after they leave the target. The technique is sensitive to boron at levels as low as 3 ppm, with a depth resolution of ±20/nm for boron in silicon. A new technique of deconvoluting this type of experimental data is described in detail. Methods are presented which eliminate the problem of spurious oscillations in deconvoluted data. Examples are shown in which the technique is used to analyze various distributions of boron in silicon.

Dielectric Breakdown in Silicon Dioxide Films on Silicon II . Influence of Processing and Materials

Abstract: The breakdown characteristics of thermally grown films on Si are shown to depend on oxide thickness, substrate doping concentration, sample preparation, presence of passivating layers, and testing temperatures. The maximum breakdown strength varies as [thickness]−0.21 below 800Aa, is essentially constant from 1000 to 2000Aa, and increases slightly (8%) with increasing testing temperature in the range −196° to +300°C. The breakdown strength is only moderately affected by the dopant‐type level in the starting silicon wafer: 1020 phosphorus atoms/cm3 in the silicon reduced the breakdown strength in 200Aa thick oxides by only 20%. The initial condition of the silicon wafer, cleaning procedure, oxidation temperature, passivation layer, and postmetalization anneal are important parameters in the control of defect‐related, low‐field breakdowns, while the oxidation ambient, substrate doping, oxide thickness, metalization, and measuring temperature have little or no influence on this process.

Structure and electrical characteristics of epitaxial palladium silicide contacts on single crystal silicon and diffused P-N diodes

Abstract: Pd2Si contacts to single crystal silicon have been made by depositing Pd at room temperature and annealing at a succession of elevated temperatures. The silicide initially formed is a single crystal, even at room temperature. Its crystal structure is uniquely related to that of the underlying silicon with the basal plane of Pd2Si making an excellent match, with respect to silicon atom positions, with the (111) plane of silicon. Understanding this epitaxy leads to an appreciation of the excellent electrical characteristics of these contacts which are shown to be superior to alloyed aluminum. For comparison, barrier height measurements reproduce earlier results of Kircher on Pd2Si formed during a high temperature (200°C) deposition of Pd.

Dependence of MOS Device Radiation-Sensitivity on Oxide Impurities

Abstract: The role of various impurities in the thermally grown silicon dioxide films of metal-oxide-semiconductor (MOS) structures has been investigated. It has been determined that aluminum and sodium within such films strongly influence the radiation-sensitivity of the corresponding MOS devices. The results of the present investigation indicate that much of the radiation-induced positive space charge accumulated within the silicon dioxide films is directly related to the drift and accumulation of ions such as those of sodium. Ionizing radiation, as fran cobalt-60 gamna rays, liberates sodium ions, which are bonded by coulombic forces to non-bridging oxygens, and consequently, the sodium ions drift in the applied gate fields. The space charge due to the accumulation of sodium near the silicon dioxide-silicon interface then causes a perturbation in the surface properties of the silicon. The insight afforded by the above model provides a basis for the fabrication of surface-controlled devices less sensitive to radiation, as well as for the fabrication of radiation dosimeters where the converse in radiation sensitivity is desired. Utilizing appropriate dopants in the silicon dioxide films the desired radiation hardening and dosimetry objectives can be realized.

Kinetics of Thermal Growth of Ultra‐Thin Layers of SiO2 on Silicon I . Experiment

Abstract: The rate of formation of very thin films thermally grown on [111] and [100] oriented silicon wafers was studied using ellipsometry to measure oxide thickness. Film thicknesses from 10–300Aa were obtained by varying oxidation time, oxidation temperature (700°–1000°C), and oxygen concentration in O2‐N2 mixtures at 1 atm total pressure. The applicability of ellipsometry for such a study is discussed. Reproducibility of oxide films grown to thicknesses of 20–30Aa was approx. ±1.0Aa. Under otherwise equal conditions the oxide thickness grown differs for [100] and [111] oriented wafers. The pressure and temperature dependence of the linear rate constant, klin, show that the growth reaction is more complicated than was suggested earlier. In particular, a different pressure dependence for the two substrate orientations used indicates that several oxygen species participate in the rate determining steps.

Thermally Stimulated Capacitance (TSCAP) in p‐n Junctions

Abstract: High‐frequency small‐signal capacitances of semiconductor junction vs temperature, from the initial conditions of filled and emptied traps in the junction depletion region, are used to determine the trap concentration and the thermal activation energies of trapped electrons and holes. Illustrations are given for silicon N + P diodes doped with gold impurity or irradiated with 1‐MeV electrons, showing the room‐temperature annealing for the latter.

Diffusion of Impurities in Polycrystalline Silicon

Abstract: The diffusion of electrically active impurities into polycrystalline silicon deposited by the thermal decomposition of silane has been studied. Both boron and phosphorus have been found to diffuse more rapidly into polycrystalline silicon than into single‐crystal silicon. The diffusivity is greatest in films deposited at about 1000°C although this maximum is a function of the deposition rate, film thickness, and substrate material as well as the deposition temperature. The maximum diffusivity is associated with a structure which has the maximum {110} texture. Although most of the films have been deposited onto amorphous SiO2, a nucleating layer of polycrystalline silicon has been found to influence the diffusion of impurities into a thick layer of polycrystalline silicon deposited over the nucleating layer. An optimum structure is obtained with a nucleating layer containing maximum {110} texture. The enhanced diffusion is tentatively attributed to diffusion down defects in the polycrystalline silicon. The...

Influence of Oxide Layers on the Determination of the Optical Properties of Silicon

Abstract: Experimental reflectance data for silicon are corrected for the presence of a surface oxide layer and analyzed using the Kramers‐Kronig relation to yield a set of optical constants for oxide‐free silicon. For etched silicon samples exposed to the atmosphere for ∼ 1 h, this layer is 12–15 A thick and has the approximate composition SiO. Absorption data are also given for epitaxial silicon on spinel and used as an aid in the analysis.

Kinetics of Thermal Growth of Ultra‐Thin Layers of SiO2 on Silicon Part II . Theory

Abstract: The thermally activated growth of oxide on silicon as a function of time obeys a linear‐parabolic relationship, the linear part of which stems from interface limited reactions. In Part I of this paper, it has been reported that this linear part cannot result from a single rate‐limiting reaction step, because the order of the over‐all reaction rate differs for different substrate orientations at a fixed temperature and varies for a given orientation as a function of temperature. A kinetic model for the reaction between silicon and oxygen at the interface is now presented to account for the experimental data . Two parallel, competing reactions are postulated to occur. In the first of these, molecular oxygen reacts directly with silicon to form silicon dioxide and atomic oxygen; the second reaction involves the dissociation of O2. The atomic oxygen thus formed, may either react with silicon or recombine to molecular oxygen. An analysis of the data shows that a difference in the activation energies (i.e., 1.91 vs. 0.58 eV) associated with these competing reaction steps is responsible for the shift in their relative importance as a function of temperature.

Low Energy Electron Spectroscopy—a Tool for Studies of Surface Vibrations

Abstract: Surface vibrations are investigated with a high resolution electron spectrometer (ΔE≈10 meV). For sufficiently low electron energies the electrons are scattered mainly by the extended electric dipole field associated with certain types of surface vibrations. The excitation of Fuchs-Kliewer surface modes in infrared-active materials is illustrated in zinc oxide. On the cleaved (111) silicon surface a surface phonon of ℏω=56 meV is found. Furthermore, the localized modes of oxygen adsorbed on a (111) silicon surface are discussed. The sensitivity of electron spectroscopy is several orders of magnitude higher than light spectroscopy.

Electron paramagnetic resonance of the lattice damage in oxygen‐implanted silicon

Abstract: The nature of the lattice damage produced at room temperature in ion‐implanted intrinsic and n‐type silicon has been studied as a function of 160‐keV O+ ion fluence using electron paramagnetic resonance (EPR). The known EPR spectra observed were the negative divacancy (Si‐G7), the neutral vacancy‐oxygen (Si‐S1), the neutral 4‐vacancy (Si‐P3), and the isotropic resonance at g = 2.0055 which is indicative of amorphous silicon. In addition, a new spectrum, labeled Si‐S2, was observed which may be the negative 4‐vacancy. Concentrations (number/cm2) for the various paramagnetic defects were determined as a function of ion fluence for fluences ranging from 1010 to 1017 O+/cm2. From these measurements we conclude that the lattice damage produced in crystalline silicon by individual ions whose maximum calculated energy density into atomic processes is ≲ 15 eV/A ion consists of simple defects such as observed in electron‐ and neutron‐irradiated silicon. Furthermore, overlap effects in the lattice damage produced b...

Gettering rates of various fast‐diffusing metal impurities at ion‐damaged layers on silicon

Abstract: High‐temperature gettering of Fe, Co, Ni, Cu, and Au by ion‐damaged surface layers on silicon wafers has been studied by Rutherford backscattering of 4He+ ions incident at 1.75 or 2 MeV. Analysis showed impurity levels in the damaged layers ranging from 1013–1017/cm2. The metals fall into two groups: those which are gettered slowly‐Fe, Co, and Au— and those gettered rapidly‐Cu and Ni. This trend is predicted by a simple diffusion model using published interstitial solubilities and diffusivities.

Interpretation of steady-state surface photovoltage measurements in epitaxial semiconductor layers

Abstract: Analysis of the steady-state surface photovoltage (SPV) method of measuring minority carrier diffusion length ( L ) has been extended to the case of an epitaxial layer on a thick substrate. In layers with thickness greater than four diffusion lengths, the measurement yields the bulk value of L . For layers thinner than 0.5 L , the measured value is that of the substrate. For intermediate thicknesses, the bulk value of L can be estimated. The method also provides a sensitive means of observing the influence of surface conditions on the absorption characteristics of silicon.