Showing papers in "Journal of The Electrochemical Society in 1975"

The Standard Thermodynamic Functions for the Formation of Electrons and Holes in Ge, Si, GaAs , and GaP

Abstract: The forbidden energy gaps of Ge, Si, , and have been used to obtain the standard Gibbs energy, enthalpy and entropy of formation of electrons and holes for each semiconductor up to the melting points. The forbidden energy gap is the standard Gibbs energy of formation of electrons and holes and the enthalpy and entropy have been obtained from the energy gap as a function of temperature and familiar thermodynamic relationships. Energy gaps as a function of temperature, available in the literature, have been fit to the semiempirical equation of Varshni and used to extrapolate the energy gaps and thereby the three thermodynamic functions to the melting points. It is well known that the energy gaps, i.e., the Gibbs energies, decrease with increasing temperature but it is not well known that the enthalpy of formation increases with temperature and that it is proportional to the slope of the familiar logarithmic plot of the intrinsic carrier concentration over vs. . Examples of the utility of the enthalpy function are given. It is the entropy that leads to the decrease in energy gap with increasing temperature and its magnitude is large near the respective melting points (10–13 cals/deg, i.e.,) arising from the interactions of electrons and holes with the lattice. The intrinsic carrier concentrations were calculated from the forbidden energy gaps and the average effective masses which were estimated for the higher temperatures.

Doped Ceria as a Solid Oxide Electrolyte

Abstract: Ceria doped with divalent or trivalent cations is a mixed conductor; conduction occurs predominantly by the motion of oxygen vacancies or by electrons, depending on the departure from stoichiometry. In order to establish the electrolytic domain at which behaves primarily as an ionic conductor with transference number , a careful study was made of the conductivity, σ, as a function of temperature and oxygen partial pressure, covering the range of 100;–10−22 atm in small steps. From these data the electrolytic domain was determined; it extends to about 10−13 atm at 600°C. When compared to calcia‐stabilized zirconia (CSZ), doped ceria shows a higher conductivity, lower activation energy (0.76 eV) for anion vacancy migration, and absence of polarization effects to lower temperatures. These results indicate that doped ceria may be an attractive candidate for fuel cells and other applications at temperatures below those at which CSZ is useful.

Electrochemical and Spectroscopic Properties of Cation Radicals III . Reaction Pathways of Carbazolium Radical Ions

Abstract: Previous work had elucidated the anodic oxidation pathways of carbazole and several N‐substituted derivatives. These studies have now been extended to seventy‐six ring‐substituted carbazoles using electrochemical and spectroscopic techniques to study the reactivity of the various substituted carbazole cation radicals. Generally, it was found that 3, 6, and 9 (N) positions are extremely reactive; if these sites are not blocked by inert substituents the cation radicals generated by electrolytic oxidation react rapidly via coupling‐deprotonation. In some cases, substituents are eliminated from the 3 and 6 positions in the cation radicals followed by coupling to form substituted bicarbazyls. In other cases, relatively stable cation radicals were obtained and their EPR and visible absorption spectra were recorded. It was found that the reactivities of substituted carbazole cation radicals are considerably greater than those of analogous di‐ and triphenylaminium ions due to the planarity of the carbazole aromatic rings.

Catalytic Decomposition of Nitric Oxide on Zirconia by Electrolytic Removal of Oxygen

Abstract: Zirconia stabilized with 8 mole per cent of scandia has a very high oxygen ion conductivity and can "pump" oxygen from oxygen‐bearing gases thus decomposing them In this study the rate of decomposition of the air‐pollutant species, nitric oxide, to harmless species (via the reaction: ) was found to be markedly catalyzed when a potential above 1V was applied across a zirconia disk coated with either a porous platinum or porous gold electrode It is known that platinum can both form oxides and catalyze the decomposition of ; whereas, gold does neither The catalytic decomposition of on platinum metal is inhibited by , such behavior being attributed to preferential chemisorption of over as well as the possible formation of an inhibiting platinum oxide surface The original rationale for this investigation was the possibility that the decomposition of might be enhanced if were electrolytically "pumped" away from a platinum electrode deposited on zirconia, keeping the platinum oxygen‐free However it was not anticipated that at high potentials dissociation rates a thousandfold that on nonporous platinum electrodes occur in the presence of either a platinum or gold porous electrode No reactivity at all was observed on a nonporous gold electrode These results suggest that catalysis occurs mainly on a surface other than the platinum or gold, namely, on the zirconia surface itself It is proposed that F‐centers on the zirconia surface formed by the applied potential are primarily responsible for the observed enhanced catalysis

Magnetic Properties of Anodic Oxide Coatings on Aluminum Containing Electrodeposited Co and Co‐Ni

Abstract: Cobalt and Co‐Ni alloy were electrodeposited into the micropores of various kinds of anodic oxide films on aluminum. Fine granular metals precipitated on the barrier layer and formed columnar structures. Although the films of cobalt or nickel showed remarkable magnetic anisotropies perpendicular to the surface, the alloy films which consisted of approximately 50% cobalt showed a strong anisotropy along the horizontal direction. Coercive forces ranged from about 500 to about 1100 oe and the density of residual magnetization rose above 1000 gauss. The films may have applications in magnetic memories and recording devices.

Rare Earth Doped Vitroceramics: New, Efficient, Blue and Green Emitting Materials for Infrared Up‐Conversion

Abstract: New, efficient, vitroceramic hosts for rare earth luminescence are discussed. Their applications to infrared up‐conversion are emphasized. Optimized compositions lead to an efficiency nearly twice as high as commercially available . As for infrared to blue efficiency, these vitroceramics are among the best compounds obtained so far. The easy preparation in air atmosphere is described. The excitation spectra have the advantage of being broader than usual for up‐conversion phosphors. Kinetic studies present some puzzling behavior with respect to sample geometry; e.g., the rise time increases fourfold with sample thickness between 0.1 and 4.5 mm. Segregation of rare earths in the microcrystalline phase rather than in the glassy one is clearly shown which explains the high efficiencies.

Properties of Sn‐Doped In2 O 3 Films Prepared by RF Sputtering

Abstract: An rf sputtering process was used without postdeposition annealing to prepare Sn-doped In/sub 2/O/sub 3/ films with low electrical resistivity (down to 2 x 10/sup -4/ ohm-cm), high visible transmission, and high infrared reflectivity (up to 93 percent at 10 ..mu..m) for applications as transparent conductors and heat mirrors. Substrate heating is accomplished entirely by the electron bombardment intrinsic to rf sputtering, rather than by using an auxiliary resistance heater. The film properties improve with increasing substrate temperature up to 650/sup 0/C, the maximum employed, and are relatively independent of other sputtering parameters. The electrical and optical properties of the films do not depend significantly on the crystallographic orientation, degree of texture, or substrate material.

Formation and Properties of Porous Silicon and Its Application

Abstract: Preparation, properties, and applications of porous silicon film were investigated. Silicon single crystal is converted into porous silicon film by anodization in concentrated hydrofluoric acid at currents below the critical current density. When an n‐type silicon was anodized, the silicon surface was illuminated to generate holes which were necessary for this anodic reaction. The growth rate of the film, from n‐type silicon, was larger than that from p‐type silicon in this experimental condition. The crystalline structure was the same as that of silicon single crystal. A new isolation technique for bipolar integrated circuits was proposed by making use of the properties of the film such that it can be formed several microns thick and oxidized easily to form an insulator. The main feature of the technique is that it provides a means to form thick insulating film inlaid through the n‐type epitaxial layer without prolonged heat‐treatment. A preliminary experiment was carried out to test the practical usage of the technique.

Low Temperature Deposition of Metal Nitrides by Thermal Decomposition of Organometallic Compounds

Abstract: Decomposition reaction of dialkylamides of boron, silicon, tin, titanium, zirconium, niobium, and tantalum was investigated. The amides of transition metals decomposed to the corresponding nitrides at 300~176 whereas those of boron, silicon, and tin yielded elemental deposits at higher temperatures. In the deposition of titanium nitride from titanium tetrakis(dimethylamide), two optimum temperatures at 400 ~ and at 800~ in nitrogen or hydrogen atmosphere were found, but in argon only low temperature deposition was possible. The low and high temperature processes are discussed in relation to mass spectral analysis of the exhaust gases formed at various decomposition temperatures of titanium amide. Metal nitrides are well known to have outstanding physical and chemical properties and have been prepared by the reactions of metal halides or hydrides with nitrogen + hydrogen or ammonia, or of metals with nitrogen (1). These reactions usually require temperatures higher than 1000~ which have limited the application of the nitrides as the useful coatings on many materials. Therefore, their preparation at lower temperature, where deformation of substrate materials can be avoided, should be important.

Thermal Oxidation of Silicon In Situ Measurement of the Growth Rate Using Ellipsometry

Abstract: The formation of oxide films on resistively heated silicon in dry oxygen was followed in situ using a computer controlled ellipsometer. For (111) silicon surfaces two distinct growth regions were observed. Our results on the growth above 300A were found to agree with previous investigations. For films 200A or less (for which little previous data exist) the kinetics did not obey any existing model of the growth process. The rate of growth of the oxide on (111) surfaces in the 20–200A region was investigated from 700° to 950°C and at oxygen pressures between 50 and 1200 Torr. A possible explanation of the thin film kinetics is given and its relation to the thick film data is discussed.

Developer Characteristics of Poly‐(Methyl Methacrylate) Electron Resist

Abstract: We report on the solubility characteristics of poly‐(methyl methacrylate) electron‐resist for developer combinations of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA). The solubility rate is determined in terms of the fragmented molecular weight which is a function of original molecular weight and the energy absorbed by the polymer in degrading to a lower molecular weight. An empirical formula for the solubility rate is , where is the fragmented molecular weight, , β, and α are constants characteristic of a given developer. The temperature dependence is characterized by an activation energy, , for a given developer. The solubility kinetics are discussed showing a rate limited process for most developer conditions. From the solubility rate and the characteristic energy absorption in the resist, the development time and contrast are defined and calculated for a variety of exposure parameters including beam energy, resist thickness, developer, developer temperature, and original molecular weight. Compared to the standard developer, 1:3 MIBK:IPA, an improved sensitivity of 10–50 times is obtained using MIBK at the expense of increased development time. For a given contrast level the development time is greatly reduced by increasing the developer temperature. A lower original molecular weight also reduces the required development time.

Diffusional Effects in Simulated Localized Corrosion

Abstract: The importance of diffusion was investigated under potentiostatic dissolution conditions with wire electrodes contained in inert supports. The artificial cavities created simulated localized corrosion conditions. Current-time behavior at voltages in excess of the critical pitting potential (>0.5V (SCE)) was examined for nickel and stainless steel specimens in concentrated chloride solutions. The effect of changing the concentration or activity gradient of the dissolving metal cations within the artificial cavity was studied by alternating the composition of the bulk solution. Solutions of FeCl/sub 2/, NiCl/sub 2/, CrCl/sub 3/, LiCl, NaCl, MgCl/sub 2/, and CeCl/sub 3/ ranging from 0.5 to 10M were used. Mass transfer models were developed for the observed transient and quasi steady-state periods of dissolution. (auth)

Optimization of the Hydrazine‐Water Solution for Anisotropic Etching of Silicon in Integrated Circuit Technology

Abstract: Anisotropic etching of silicon with the hydrazine‐water mixture is studied and characterized for its practical use in integrated circuit technology. The solution is applied to {100} wafers where the etch presents a v‐shaped cross section limited at the side‐walls by {111} planes and at the bottom by a {100} plane. The etching process is evaluated in terms of the etch rate of the {100} plane, quality of side‐walls and bottom surface, and corner rounding. It is shown that the results are both concentration and temperature dependent. The optimal temperature for the etching process is found to be 100°C for both simple temperature control and high quality etching. It is also shown that the optimal mixture concentration must be choesn according to the particular use of the anisotropic etching. The optimal volume concentrations of hydrazine for the various applications are: 65% for VMOS devices and for v‐groove isolation rings, 70–80% for two‐level structures with flat bottom surface, and for electrode and sensor fabrication.

On the Kinetics of the Breakdown of Passivity of Preanodized Aluminum by Chloride Ions

Abstract: The kinetics of passivity breakdown and nucleation of pitting of preanodized aluminum by chloride ions has been investigated using aluminum supporting oxide films of reasonably well‐known thickness and structure. The kinetics of passivity breakdown at the steady‐state, critical pitting potential is influenced by chloride ion concentration, temperature, and oxide film thickness; it was found to be independent of solution pH in the range 5–10. It is postulated that passivity breakdown and nucleation of pitting at the critical pitting potential occurs by a process of Cl− adsorption (assisted by the field at the oxide‐solution interface) on the hydrated oxide surface and formation of a soluble, basic chloride salt with the lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble, basic, aluminum chloride salt once initiated is likely to continue in an "autocatalytic" fashion until the oxide is locally "penetrated" and dissolution of the substrate metal begins.

Growth and Structure of Nickel Oxide on Nickel Crystal Faces

Abstract: The structures of films of 300A‐15μ thick formed on (100), (110), and (111)Ni crystal faces at temperatures in the range 500°–800°C were investigated by electron microscopy and x‐ray diffraction. The oxide was initially polycrystalline but rearranged as the oxide thickened to major epitaxial relationships with the metal substrate. These relationships were characterized by coincidence between the close‐packed directions of the metal and oxide; the number and type of oxide orientations were correlated with the number of close‐packed directions in the metal faces. Oxide thicker than 1μ exhibited preferred {100} and {111} orientations. The oxide on (100) and (111)Ni exhibited the highest preferred orientation and a duplex layer structure consisting of equiaxed crystallites in the inner layer and columnar ones in the outer layer. These findings are rationalized in terms of a diffusional model for the growth of these oxide layers in which the reaction rate is determined by boundary and lattice diffusion of nickel through nickel oxide.

The Diffusion of Ion‐Implanted Arsenic in Silicon

Abstract: In order to characterize implanted‐diffused As layers in Si and to develop general processing information, impurity profiles were determined by secondary ion mass spectrometry (SIMS) and differential conductivity measurements. An analysis of these profiles is given which has yielded information regarding the diffusion of As and the electrical quality of these implanted‐diffused layers. It is shown that implanted‐diffused As profiles with can be described by a Chebyshev polynomial approximation to the diffusion equation with concentration‐dependent diffusivity. The diffusion of As is not dependent upon the furnace ambient, but As pile‐up within 200–400A of the Si surface does occur during diffusion in an oxidizing atmosphere. It is also shown that implanted‐diffused As layers show higher electrical activity for diffusion temperatures below 1100°C than layers diffused from chemical sources. For implanted As layers in which the peak concentration is greater than the solubility limit, the fraction of electrically active As increases at a rate proportional to .

Boron Diffusion in Silicon‐Concentration and Orientation Dependence, Background Effects, and Profile Estimation

Abstract: Boron is almost universally used as a p‐type dopant in Si devices. Since this dopant is introduced into the Si lattice under a wide range of diffusion conditions, effects are often observed which appear anomalous because the mechanism of B diffusion is not completely understood. Anomalous effects that have been observed include a concentration‐dependent diffusion coefficient, orientation‐dependent diffusion under oxidizing conditions, and retarded or accelerated diffusion in the presence of n‐type impurities. This paper discusses a model of B diffusion which can be used to explain these observed effects. Data and arguments are presented which show that B diffuses via a monovacancy mechanism when the diffusion is performed in a nonoxidizing ambient. A donor‐type vacancy is responsible which has a presumed energy level of as suggested from the quenching experiments of Elstner and Kamprath. High concentration B diffusions into Si over a 550°C temperature range in neutral ambients result in profile data that fit a normalized universal curve which is a polynomial approximation to the solution of the diffusion equation with concentration‐dependent diffusivity. From this result, useful curves of surface concentration vs. resistivity and junction depth are presented.