Showing papers in "Journal of The Electrochemical Society in 1972"

Kinetics of the Deposition of Inert Particles from Electrolytic Baths

Abstract: To explain the peculiarities shown by the codeposition of inert particles from electrolytic baths, a mechanism based on two successive adsorption steps is proposed. In the first step the particles are loosely adsorbed, and they are in equilibrium with the particles in suspension. In the second step the particles are irreversibly adsorbed. Making a few elementary hypotheses about the mechanism that governs the two steps it is possible to deduce a general expression relating the concentration of the embedded particles to the suspension concentration and the electrode overpotential. This relationship is verified experimentally.

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.

Contact Resistance and Contact Resistivity

Abstract: This paper mainly offers guidance to the technologist who has to characterize metal‐semiconductor contacts for process development and production control. To abolish confusion clear definitions are proposed for the terms contact resistance and contact resistivity. Based on these definitions, methods of determining contact resistivity are discussed, revealing the common source of error of the methods and making comparisons. New methods like the TLM method are described and included in the comparison. Results of contact resistivity measurements on Al‐Si contacts over a wide range of silicon surface doping are presented.

Double Layer Capacitance of Iron and Corrosion Inhibition with Polymethylene Diamines

Abstract: The effect of α,ω‐polymethylenediamines on the corrosion of iron in deaerated was investigated by polarization measurements and colorimetric analysis of solution. The adsorption of these inhibitors at the metal/solution interface was monitored by measurement of the double layer capacitance using the single pulse method. 1,3‐propanediamine was found to be a better inhibitor than ethylenediamine, but no further improvement in per cent inhibition resulted upon increasing the chain length from . Increased inhibitor efficiency for hydrocarbon chains longer than eight carbon atoms was attributed to the concomitant decreased solubility. On a relative solubility basis, the C6‐diamine was more efficient than the C12‐diamine, although both inhibitors produced 90% inhibition at a reduced concentration of 0.1. The double layer capacitance was approximately constant at 21 µF/cm2 for the C2‐ through C8‐diamines, and alternated between 6 and 14 µF/cm2 for the C9‐ through C12‐diamines. The constancy at 21 µF/cm2 suggets that diamines with up to 8 carbon atoms are adsorbed in the same configuration, probably the flat position. The subsequent reduction and alternation in capacitance is believed due to a structuring of the adsorbate similar to that in the bulk where certain physical properties oscillate with carbon number. Colorimetric analysis of solutions with and without additions showed the dissolution rates to be higher than those measured by the polarization technique, possibly due to the "chunk" effect, in which dislodged grains of metal contribute to the total but not faradaic corrosion.

Highly Conductive, Transparent Films of Sputtered In2 − x Sn x O 3 − y

Abstract: Highly conductive, transparent films of have been deposited by d‐c diode sputtering with Ar, O2, N2, Xe, and O2‐Ar mixtures. Sputtering targets with different ratios were utilized and the best results were obtained with pure Ar or Xe gas and targets containing 9–13 mole percent (m/o) . The lowest film resistivity achieved was , but routine films had resistivity values of about . The use of a very low sputtering gas throughput (10−2–10−1 Torr liter/sec) was found to be necessary to develop films with a slight oxygen deficiency. Targets differing in density (porosity) differ in their susceptibility to reduction so that sputtering conditions depend on target density. The films have excellent adherence and will tolerate cleaning, heating, polishing, and bonding without failure. They may be etched in heated acids with standard photoresist techniques used to define electrode geometry. Exposure of the films to temperatures of 500 °C in air will cause an approximate factor of 3 increase in resistance at room temperature. Sputtered films with sheet resistance of 1.6 ohms/square, 73% light transmission, and 14% reflection at 500 nm have been obtained. Suitable antireflection coated films of 5–7 ohms/square possessing over 97% light transmission appear feasible.

Luminescence and Structural Properties of Thiogallate Phosphors Ce+3 and Eu+2‐Activated Phosphors. Part I

Abstract: Thiogallate compounds represented by the formula were prepared by solid‐state reaction. Single crystals of the alkaline earth derivatives were also obtained by vapor transport of the corresponding polycrystalline material. X‐ray diffraction analyses of the single crystals show that is cubic belonging to space group while and are isomorphous belonging to the orthorhombic space group . X‐ray powder diffraction results on the other derivatives indicate that they are all isostructural with the Sr analogue. The alkaline earth thiogallates are the basis of a new type of sulfide phosphor. Rare earth ions readily substitute for the alkaline earth in the host lattice resulting in phosphors that fluoresce strongly under ultraviolet and cathode rays. The luminescence properties of the host compounds and the Ce+3 and Eu+2‐Activated phosphors are described.

On the Deposition and Dissolution of Zinc in Alkaline Solutions

Abstract: The zinc/KOH‐zincate electrode reaction was investigated under high purity conditions with galvanostatic and potentiostatic transient techniques in the 0.1–3.0M and 0.0001–0.5M zincate concentration range. The exchange current density was found to be between 8 and 370 mA/cm2, with 40 mV/decade anodic and 120 mV/decade cathodic nominal Tafel slopes; an overpotential range of ± 100 mV was covered. The cathodic reaction orders were 1 for zincate, and −1 for hydroxyl ions. A four‐step mechanism, consistent with the kinetic data, is suggested. It consists of four consecutive dissociation reactions of the zincate complex, with two of them incorporating a single electron charge transfer. The rate‐determining step is The mechanism of the anodic and cathodic reactions is the same. The transients indicate only double layer charging and charge transfer processes. No surface diffusion effects or intermediate build‐up was observed (no pseudocapacitance). A rationalization is given for the mechanism. The effect of zinc surface preparation is discussed.

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.

Electrochemistry of Cleaner Environments

Abstract: Until the late 1960s, there was little public concern about environmental pollution It was a matter of experience that pollutants (sewage, industrial wastes) were produced and rejected into what seemed to be the vast expanse of nature—air, rivers, and seas—wherein, somehow, they vanished Peaks of discontent remain registered,† but, by and large, environmental concerns had no place on political platforms

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.

Kinetics of Iron Corrosion in Concentrated Acidic Chloride Solutions

Abstract: The kinetics of active iron dissolution at 25°C has been studied in deaerated 1N and 6N chloride solutions for hydrogen ion concentrations of 0.1–6.0N. For 1N chloride solutions with , the dissolution reaction is described by anodic Tafel slope and electrochemical reaction order with respect to hydrogen ion activity . These parameters are characteristic of a dissolution mechanism in which chemisorbed halide ions interact with adsorbed hydroxyl ions in a two‐electron rate‐determining step. For 6N chloride solutions, this mechanism holds only over a narrower (H+) region up to 0.24N, in which . With increased ; and for , indicating that the hydrogen ion (and no longer the hydroxyl ion) catalyzed the dissolution reaction. A positive value of ensues for synergistic adsorption of hydrogen ions on the halide ion covered surface. A formal detailed dissolution mechanism is proposed, giving and , in agreement with experiment. Alternate dissolution mechanisms including one‐electron transfer schemes are discussed.

TiO2 Film Properties as a Function of Processing Temperature

Abstract: Thin film was produced at 150°C by chemical vapor deposition using hydrolysis of tetraisopropyl titanate. Films were amorphous as grown, but annealing in air caused crystallization, with anatase formed beginning at 350°C and rutile at 700°C. Density and index of refraction increased substantially with increasing anneal temperature, while etch susceptibility in and decreased. Comparison with literature data showed two groups of processes. One group yields films having properties that gradually approach those of rutile with increasing process temperature. The other group gives rutile directly at moderate temperatures. Deposition of amorphous film, followed by etching and annealing is suggested as a means for pattern definition.

On the Mechanism of Low‐Temperature Oxidation (23°–450°C) of Polycrystalline Nickel

Abstract: The oxidation of "clean" nickel has been investigated from 24° to 450°C at oxygen pressures of . Ultra‐high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. Oxygen uptake was measured manometrically with a capacitance gauge of submonolayer sensitivity. Initial rapid oxygen adsorption (and place exchange) on nickel was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8–30Aa. Growth of thicker films was in accord with a parabolic rate law, transport through the oxide occurring predominantly via easy diffusion paths. The value of 41 kcal·mole−1 calculated from an Arrhenius plot of the parabolic rate constants from 300° to 450°C is an approximate measure of the activation energy for growth via leakage paths. A p1/6 dependence of the parabolic growth rate on oxygen pressure was found at 450°C.

Heteroepitaxial Thermal Gradient Solution Growth of GaN

Abstract: The growth of single‐crystal epitaxial layers of onto (0001) oriented sapphire substrates from the liquid phase is shown to require three conditions:(i) the partial pressure of in the H2 ambient, greater than the equilibrium pressure, (ii) the growth melt positioned in a thermal gradient to transport the dissolved to the growth interface, and (iii) the control of nucleation by the addition of Bi to the growth melt. Studies of growth at temperatures from 850° to 1050°C show that the layer thickness, , is approximately linear in time and varies with growth temperature and atom fraction of Ga, in the growth melt. When , internal cracks in the basal plane hexagonal directions develop at the layer‐substrate interface and for they propagate to the surface and are thermally etched. A description is given of the interaction of liquid Ga with as a function of and . The low solubility of in Ga ( fraction at 1150°C) prevents useful growth by slow cooling of the melt. The inability to change the electron concentration, , with Zn doping and the decrease of with in the growth melt support but do not unambiguously confirm the model that the native donor is a nitrogen vacancy

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.

Thermally Stimulated Currents and Voltages and Dielectric Properties

Abstract: Experimental techniques for charging and observing thermally stimulated currents and voltages (TSC and TSV) in polymers and crystals are described and an outline is given of the theory of the processes. The polymers are corona charged, and trapping takes place near one surface. In an attempt to determine the microscopic nature of the traps, a study is made of a polyolefin series of ten polymers. Charge storage is shown to take place mainly along the chains themselves and through caging between neighboring molecules. In addition, the corona itself may produce changes in the polymers to create primary trapping sites. Charge storage stability is a function of electronegativity of the ions, symmetry along the chains, and packing density. The crystal work consists of a study of impurity‐vacancy (I – V) dipoles in doped alkali halides, such as , Eu++, Yb++, and Ca++. The dipoles are field polarized. Analysis of the thermally stimulated dipolar peaks yields relaxation times, activation energies, and dipole concentrations. Other I – V dipole phenomena that may be studied with these techniques are described. A comparison is made between information obtainable from TSC and the more normal dielectric constant‐loss tangent measurements, and we conclude that TSC is a valuable aid in the characterization of insulators. These studies also yield information on the basic electrical conduction mechanisms in insulators. The paper concludes with suggestions for further work and practical applications.