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Nov 1974

Volume 11, Issue 6, pp. 935-1195


Phenomenology of metal-semiconductor electrical barriers

T. C. McGill

J. Vac. Sci. Technol. 11, 935 (1974); http://dx.doi.org/10.1116/1.1318709 (8 pages) | Cited 10 times

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The phenomenological rules governing the values of electrical barriers between metals, and semiconductors or insulators are reviewed. The barrier energies on ionic insulators are shown to vary strongly with metal electronegativity, while in the case of covalent semiconductors, the barrier energies are relatively independent of the metal. The barrier energy from the metal Fermi level to the conduction band of the semiconductor is shown to be approximately two thirds of the semiconductor band gap with certain exceptions. The success of a simple barrier model in accounting for the properties of the barrier are reviewed. The variation of barrier energy with electrical field is reported for Al-SiO2, Al-GaSe, and Al-GaAs and compared with simple theory including image-force lowering and field penetration into the metal. Transport through interfacial barriers is illustrated by discussing transport through metal-GaSe-metal structures and metal-InAs Schottky barriers.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.-c Electronic transport in interface structures

Schottky barriers and plasmons

J. C. Inkson

J. Vac. Sci. Technol. 11, 943 (1974); http://dx.doi.org/10.1116/1.1318710 (4 pages) | Cited 7 times

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The changes in the electron exchange and correlation potential are related to the collective excitation at the interface of a metal semiconductor junction. They are shown to change discontinuously across the band gap, and the possible effects on the barrier formation are discussed. The possibility of surface superconductivity through exciton and plasmon exchange is considered briefly.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Chemical bonding at metal-semiconductor interfaces

J. C. Phillips

J. Vac. Sci. Technol. 11, 947 (1974); http://dx.doi.org/10.1116/1.1318711 (4 pages) | Cited 10 times

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Trends in the I–V characteristics of metal-semiconductor interfaces can be analyzed in terms of the atomic configurations at interfaces as well as the redistribution of electronic charge which occurs because of chemical bonding at the interface. The atomic configurations, in turn, depend on the thermal history of the interface, which can be discussed from several points of view. The chemical bonding picture can be contrasted with the more traditional approach based on surface states, such as those associated with dangling bonds on free semiconductor surfaces.
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73.40.Ns Metal-nonmetal contacts
73.20.At Surface states, band structure, electron density of states

A simplified self-consistent model for image force and interface charge in Schottky barriers

C. R. Crowell

J. Vac. Sci. Technol. 11, 951 (1974); http://dx.doi.org/10.1116/1.1318712 (7 pages) | Cited 18 times

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Some qualitative features are shown for an electrostatically self-consistent solution, initially without correlation and exchange forces, for the effect of electrons which tunnel from the metal of a Schottky barrier into the energy band gap of the semiconductor. The effect of an incremental electric field in the bulk semiconductor is deduced from a simple analytical treatment. In covalent semiconductors most of the incremental electric field terminates in the semiconductor in a manner almost independent of the nature of the metal, i.e., the effective “metal” electrode exists inside the bulk semiconductor. This is not true for ionic semiconductors. When the “metal” electrode location is used as the origin for the image force, a normal square root of the field dependence of the Schottky image force lowering is predicted at low electric fields and a linear dependence is predicted at high electric fields, both as reported recently by Andrews. The model also predicts the order of magnitude of the very small barrier variation between p- and n-type semiconductors. Interface contamination is predicted to have a very small effect on the barrier height provided the dopant occurs within the range of the tunneling electrons. If the dopant is deeper, however, and converts the semiconductor type, the effective barrier height, charge storage and photosensitivity are radically changed. It is shown that this phenomenon creates effective Schottky barrier configurations that have softer reverse current-voltage characteristics than an uncontaminated barrier. These conclusions are reinforced by measurements on Hf-n-type-Si Schottky barriers.
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73.30.+y Surface double layers, Schottky barriers, and work functions

Properties of carriers at the Si-SiO2 interface in MOSFET structures

P. J. Stiles

J. Vac. Sci. Technol. 11, 958 (1974); http://dx.doi.org/10.1116/1.1318713 (4 pages)

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A description of the electrical properties of carriers in inversion layers in a Si-SiO2 system at low temperatures is given. An attempt is made to relate the observed properties to the properties of the host interface.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Evidence for a mobility edge in inversion layers. II

Frank Stern

J. Vac. Sci. Technol. 11, 962 (1974); http://dx.doi.org/10.1116/1.1318714 (3 pages) | Cited 2 times

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Potential fluctuations in inversion layers at semiconductor-insulator interfaces are expected to give rise to a mobility edge separating localized from delocalized states. Recent experimental and theoretical work on this subject is briefly described.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electron beam probe studies of semiconductor-insulator interfaces

W. R. Bottoms and D. Guterman

J. Vac. Sci. Technol. 11, 965 (1974); http://dx.doi.org/10.1116/1.1318715 (7 pages)

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An electron beam of diameter as small as 100 Å may be employed to study MOS structures, providing information about the surface topography (secondary electron imaging), surface chemical composition (Auger electron spectroscopy), bulk chemical composition (x-ray fluorescence), as well as the structure of interface regions with high spatial resolution. The penetration depth of the beam and therefore of the excited volume can be altered by adjusting the accelerating voltage and the incident angle. Images of the internal surfaces of MOS structures are formed due to variatons in the metal-insulator barrier height, the semiconductor-insulator barrier height, defects within the oxide or at the interfaces, and topography causing localizing high-field conditions. These mechanisms give rise to small ac signals in the current induced across the structure by the electron beam. These signals may then be amplified and used to modulate the intensity on a CRT. Several different structures have been observed at the interfaces in MOS systems using this technique. Electrical measurements and bias thermal stressing experiments have been used to determine the nature of the structures responsible for observed images.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling

The role of the metal-semiconductor interface in silicon integrated circuit technology

J. M. Andrews

J. Vac. Sci. Technol. 11, 972 (1974); http://dx.doi.org/10.1116/1.1318716 (13 pages) | Cited 31 times

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A typical medium-scale integrated (MSI) circuit requires hundreds of metal-semiconductor (M–S) junctions that are utilized for rectification, interconnection of device elements, and termination to external circuits. Comparison has been made between two metallization technologies, based upon the possible metallurgical reactions with Si: (1) nonreactive, such as evaporated aluminum, and (2) reactive, such as PtSi. Ohmic and rectifying contacts have been contrasted on the basis of the dominant current conduction mechanisms at the M–S interface. Current transport has been characterized in terms of the height and thickness of the potential energy barrier arising from thermal equilibrium among charge carriers between dissimilar conductors. Thermionic emission of electrons and holes provides the first illustration of conduction over a thick potential barrier (≫100 Å), resulting in a rectifying contact (Schottky barrier diode). Thus, Schottky diode currents are exponentially dependent upon potential barrier height and inverse temperature. The contrasting illustration deals with a thin barrier (≪100 Å) that conducts electrons and holes by quantum mechanical tunneling and forms ohmic contacts with resistance controlled only by contact size and underlying silicon resistivity. The final section covers two possible problems associated with silicon integrated circuit (SIC) fabrication. In the first example, a layer of oxide, too thin to be visible by optical interference (<500 Å), can prevent proper contact formation. A method of observation, which makes use of hydrostatic surface tension, has been presented with experimental results on SiO2 films. Successive etching has revealed a detection limit of 11–13 Å. The second deleterious phenomenon to be treated is the electrical degradation of Schottky barrier rectification associated with nonplanar penetration of metals into silicon. The destruction of the planar M–S interface could result from either undesired alloy eutectics or metallic precipitation.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Ns Metal-nonmetal contacts

Some recent studies of very thin SiO2 films

Y. J. van der Meulen

J. Vac. Sci. Technol. 11, 985 (1974); http://dx.doi.org/10.1116/1.1318717 (5 pages) | Cited 2 times

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An overview is given of some recent studies involving characterization of thin SiO2 films. Topics discussed include the stoichiometry of not intentionally contaminated films, the impurity distribution of phosphorus at the Si-SiO2 interface, and some methods of studying these films in a dynamic mode, i.e., while changes occur in their structure or thickness.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology

Atom movements occurring at solid metal-semiconductor interfaces

J. O. McCaldin

J. Vac. Sci. Technol. 11, 990 (1974); http://dx.doi.org/10.1116/1.1318718 (6 pages) | Cited 10 times

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Solid metal-semiconductor interfaces often undergo chemical reaction at rather low temperatures, in some cases not much above room temperature. After some general discussion of these reactions, more detailed consideration is given to simple noncompound-forming systems, and, in particular, to the Si-Al, Ge-Al, and Si-Au systems. Diffusive transport of Si or Ge in these solid metallizations is very rapid, though the converse process, diffusion of metal in solid Si or Ge, is usually so slow as to be negligible. The interface reaction itself is less well understood but is becoming controllable in intrinsically favorable cases like Ge-Al and in other cases by more sophisticated means.
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68.35.Fx Diffusion; interface formation

Tunneling in thin MOS structures

J. Maserjian

J. Vac. Sci. Technol. 11, 996 (1974); http://dx.doi.org/10.1116/1.1318719 (8 pages) | Cited 71 times

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Recent results on tunneling in thin MOS structures are described. Thermally grown SiO2 films in the thickness range of 22–40 Å have been shown to be effectively uniform on an atomic scale and exhibit an extremely abrupt oxide-silicon interface. Resonant reflections are observed at this interface for Fowler-Nordheim tunneling and are shown to agree with the exact theory for a trapezoidal barrier. Tunneling at lower fields is consistent with elastic tunneling into the silicon direct conduction band and, at still lower fields, inelastic tunneling into the indirect conduction band. Approximate dispersion relations (E-k, E-κ) are obtained over portions of the silicon-dioxide energy gap and conduction band.
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73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Surface polaritons—propagating electromagnetic modes at interfaces

E. Burstein, W. P. Chen, Y. J. Chen, and A. Hartstein

J. Vac. Sci. Technol. 11, 1004 (1974); http://dx.doi.org/10.1116/1.1318673 (16 pages) | Cited 43 times

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Surface polaritons are interface electromagnetic modes whose propagation constants depend on the dielectric constants and magnetic permeabilities of the interfacing media. We discuss here (i) the nature of the modes which exist at single-interface and at slab (two-interface) configurations, (ii) the methods for coupling bulk polaritons and surface polaritons, and (iii) the use of surface polaritons as electromagnetic probes of surfaces and interfaces.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

The influence of sodium on the Si-SiO2 interface

T. H. DiStefano and J. E. Lewis

J. Vac. Sci. Technol. 11, 1020 (1974); http://dx.doi.org/10.1116/1.1318674 (5 pages) | Cited 16 times

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Internal photoemission and thermionic emission are used to determine the dipole polarization layer produced by sodium ions at a Si-SiO2 interface. The electronic energy barrier at the interface is reduced by the sodium ion dipole from 4.25 eV for a clean Si-SiO2 interface to a saturation limit of 2.6 eV for a sodium coverage of 1.3×1015 Na∕cm2. The interface is quite sensitive to the presence of sodium, since only about 0.01 monolayer of sodium is sufficient to cause an appreciable reduction of the threshold for internal photoemission.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
79.40.+z Thermionic emission

Behavior of ions in SiO2

R. Williams

J. Vac. Sci. Technol. 11, 1025 (1974); http://dx.doi.org/10.1116/1.1318675 (3 pages) | Cited 5 times

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Several methods that have been used to inject ions into layers of thermally grown SiO2 are reviewed and compared. We have studied the injection of various ionic species through the free surface of the oxide. A thin layer of a salt containing the desired ion is coated on the surface which is then charged with a corona discharge of the proper polarity. Some positive ions move through the oxide under these conditions while others do not. The determining factor is apparently the ionic radius. The smallest negative ion is F− and this shows some mobility under these conditions, though less than the smaller positive ions.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films

Metal powder production by vacuum atomization

J. M. Wentzell

J. Vac. Sci. Technol. 11, 1035 (1974); http://dx.doi.org/10.1116/1.1318676 (3 pages) | Cited 1 time

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The problems inherent in metal atomization have spurred the development of vacuum atomization, a process showing much promise. In this process, the potential energy for atomization can be stored within the molten metal, which increases the efficiency. Also, the higher tap densities of vacuum-atomized powders, as compared with argon-atomized powders, is a distinct advantage. Alloy powders based on Ni, Co, Fe, Cu, Al, and misch metal have all been made successfully by this process. Powder metallurgy will play a significant role in this era of conservation and cost reduction, and vacuum atomization has shown that the unconventional approach may offer the most practical solutions to some of our current problems.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys

Trace-element effects in vacuum-melted superalloys

William B. Kent

J. Vac. Sci. Technol. 11, 1038 (1974); http://dx.doi.org/10.1116/1.1318677 (9 pages) | Cited 3 times

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The effects of lead, bismuth, silver, and selenium additions (at three levels each) on the workability and mechanical properties of Unitemp 718 are reported. Findings of this study include: (i) no significant effects on room temperature or 1200 °F tensile or yield strength were observed; (ii) 1200 °F stress rupture lives, and stress rupture and tensile ductilities decreased sharply with increasing content of all four trace elements: (iii) only selenium additions had a detrimental effect on workability. The lack of correlation of analytical data among laboratories noted in this study underscores the need to improve the reliability and reproducibility of analytical data through the establishment of standards for trace elements analyses.
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81.05.Bx Metals, semimetals, and alloys
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Electrical and magnetic interactions in vacuum-arc remelting and their effect on the metallurgical quality of specialty steels

R. Schlatter

J. Vac. Sci. Technol. 11, 1047 (1974); http://dx.doi.org/10.1116/1.1318678 (8 pages)

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The principal interactions between melting current, self-generated magnetic fields, and structural parts of the vacuum arc furnace, and the effect of unsymmetrical stray fields on arc characteristics, pool behavior, and metallurgical quality are briefly reviewed. Various macrosegregation defects are caused by unbalanced electromagnetic interactions affecting pool rotation and the solidification process. The procedure for measuring magnetic-flux density is described, and the results obtained on a large vacuum arc furnace with different bus-bar arrangements are presented. These results, along with extensive operational observations, strongly pointed out the importance of properly located current connections and coaxial current flow on furnace operation and ingot quality. Corrective actions and modifications of the current transmission system to eliminate nonuniform magnetic stray fields from the arc and melting zone are outlined. A coaxial, electromagnetically “clean” configuration of the entire current circuit to and within the furnace is a most important requirement for consistent consumable-electrode melting operation and reliable avoidance of macrosegregations in specialty steels and alloys. A discussion of controlling electromagnetic interactions by careful engineering of the current supply layout and incorporation of these concepts into an advanced furnace design concludes the paper.
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81.20.-n Methods of materials synthesis and materials processing
81.05.Bx Metals, semimetals, and alloys

Kinetics of solute removal during electron-beam and vacuum-arc melting

R. J. Andreini and J. S. Foster

J. Vac. Sci. Technol. 11, 1055 (1974); http://dx.doi.org/10.1116/1.1318679 (5 pages)

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A steady-state, nondiffusional control model has been derived which describes the kinetics of dilute metallic-solute removal from molten alloys using electron-beam or consumable vacuum-arc-refining techniques. Although the model is developed in terms of a binary alloy, good agreement between theory and experiment was found for the removal of minor components from a complex automotive steel scrap. The model can also be used to predict the melt-stock solute concentration required to attain a desired solute concentration in the final ingot for a given melt rate. Conditions under which calculated results from the model are valid are also discussed.
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81.20.Ym Purification

The effects of nonconsumable melting on the quality of Ti 6Al∕4V

G. Douglas Willette

J. Vac. Sci. Technol. 11, 1060 (1974); http://dx.doi.org/10.1116/1.1318680 (7 pages)

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A nonconsumable electrode-skull casting process designed to remove refractory inclusions by gravity separation is described. Examples of potential advantages are: (i) All forms of raw materials can be melted in any desired ratio; (ii) there is no vaporization find loss of volatile alloy elements, and thus no need for extensive chemical testing and adjustments before remelting; (iii) cast remelt electrodes are produced directly, without prior compacting, welding, and consumable melting. With this process, better chemical homogeneity was obtained, and nitride-type as well as high-density inclusions were removed.
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81.20.Ym Purification
81.05.Bx Metals, semimetals, and alloys

Casting of metallic filament and fiber

Robert E. Maringer and Carroll E. Mobley

J. Vac. Sci. Technol. 11, 1067 (1974); http://dx.doi.org/10.1116/1.1318681 (5 pages) | Cited 18 times

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The production of metallic fiber and filament directly from the melt has been practiced for some years. However, the application of these techniques has been limited due to materials-compatibility problems. Two new fiber-casting methods have been developed: Crucible Melt Extraction and Pendant Drop Melt Extraction. Both methods involve bringing the edge of a rotating disk into contact with a source of molten metal. Molten metal solidifies on the periphery of the disk, adheres there for a short time as it is removed from the melt source, and is then spontaneously released from the disk in the form of solid fiber. Both methods significantly reduce the technical difficulties heretofore associated with fiber casting and are amenable to operation in air, inert atmosphere, or vacuum. Metals as diverse as tin and niobium have been fiberized successfully.
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81.10.Fq Growth from melts; zone melting and refining

Centrifugal casting of misch-metal liners for the 105-mm projectile

W. H. Pfeifer and D. P. Moak

J. Vac. Sci. Technol. 11, 1072 (1974); http://dx.doi.org/10.1116/1.1318682 (12 pages)

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Centrifugal casting was investigated as a process to place an integral liner of misch metal within the standard 105-mm projectile body. Vacuum induction-melting equipment enabling molten misch metal to be poured into a vertically rotating projectile body that can be heated to temperatures up to ≈1600 °F was employed. Analytical solidification studies were made to help establish experimental guidelines. These included calculations of rotational velocity required to provide the desired misch-metal distribution, a simple heat balance to denote mold-heating effects from the heat content of the misch metal, and estimation of solidification times as a function of both misch metal and projectile-body temperatures. Both the misch metal employed and the as-received projectile bodies were thoroughly characterized to provide baseline data, and an annealing study of the AISI Type 1018 steel projectile body was made to determine the temperature at which serious degradation of the yield strength (provided by extensive cold working) occurs. Casting experiments were conducted to establish process parameters and demonstrate feasibility of the centrifugal casting technique. Most castings were destructively examined to determine the liner quality, the bond between the liner and projectile body, and the final properties of the projectile body. These experiments revealed that projectile-body temperatures of 1100–1150 °F are critical in effecting a compromise between retention of the cold-worked properties of the steel and attainment of the desired casting profile and liner-projectile body bonding.
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81.10.Fq Growth from melts; zone melting and refining

The application of transmission electron microscopy through the use of thin foils

D. M. Moon

J. Vac. Sci. Technol. 11, 1084 (1974); http://dx.doi.org/10.1116/1.1318683 (3 pages)

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Basic procedures of TEM are described, and the recent advances in the technique and in its application are reported. Among the most recent developments are: (i) high-voltage electron miscroscopy, which lessens the stringement requirement for producing foils as thin as 2000−500 A; and (ii) scanning transmission electron microscopy, which offers benefits over conventional TEM, e.g., an increase in penetrating powder by a factor of about 3, and a time-resolved image. The application of these techniques, as well as energy analysis, will become widespread as more instruments become available, enlarging further the number and types of problems capable of solution with TEM.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Some applications of Auger electron spectroscopy to metallurgical problems

T. W. Haas and D. J. Pocker

J. Vac. Sci. Technol. 11, 1087 (1974); http://dx.doi.org/10.1116/1.1318684 (6 pages) | Cited 2 times

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The requirements for applying Auger electron spectroscopy (AES) are relatively simple: (i) a vacuum environment to maintain a stable, surface condition during the measurement interval and to avoid electron-gas collisions; (ii) excitation sources to induce Auger transitions in surface atoms; (iii) an electron spectrometer; and (iv) specimens sufficiently small to fit into the vacuum system and of such geometry that the spot of interest can be properly located with respect to the spectrometer. The applications of AES discussed herein are depth profiling of the chemical composition in the near-surface region, investigation of chemical environment of elements in surface regions, determination of changes in the chemistry of surface atoms, quantitative surface analysis, investigation of grain-boundary segregation and its effect on embrittlement and subsequent fracture. Auger spectra are shown for a fractured Ti-6Al-4V specimen, a René-alloy-specimen surface, an alumina particle imbedded in a René alloy, and an embrittled tungsten material.
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81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Secondary-ion mass analysis: Instrumentation, data interpretation, and applications

Bradway F. Phillips

J. Vac. Sci. Technol. 11, 1093 (1974); http://dx.doi.org/10.1116/1.1318685 (7 pages) | Cited 2 times

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The field of secondary-ion mass analysis is discussed starting with the historical events leading up to present-day instrumentation. The two principal types of instruments are described in some detail, as well as anticipated new developments. Problems in data interpretation and quantitative treatment of data are discussed as a background for the presentation of several examples of the technique's usefulness.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
07.75.+h Mass spectrometers

Electron-probe microanalysis—a capsule survey

Harvey Yakowitz

J. Vac. Sci. Technol. 11, 1100 (1974); http://dx.doi.org/10.1116/1.1318686 (5 pages)

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A brief overview of the way in which electron-probe microanalysis can be used to obtain information from microvolumes comprising 10−12 g or less of specimen material is presented. Elemental identification, distribution, and quantitative analytical procedures are outlined. Energy-resolving detectors and wavelength-dispersive spectrometers are compared; analysis of elements with atomic number < 11 is also briefly considered in this context. An example of the solution of a service failure by means of elemental-distribution mapping is offered. Finally, an indication is given of the accuracy which can be expected from quantitative electron-probe microanalysis.
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82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Vacuum heat treatment today

Herbert W. Westeren

J. Vac. Sci. Technol. 11, 1105 (1974); http://dx.doi.org/10.1116/1.1318687 (4 pages)

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Vacuum heat-treating equipment is defined as “controlled-atmosphere” equipment—controlled in quality and in quantity with special emphasis on partial pressures as well as total pressures. This concept is substantiated by a brief review of vacuum heat-treating equipment from pioneer studies by a leading vacuum furnace manufacturer, the development of fibrous graphite furnaces, vacuum oil-quench equipment, and vacuum water-quench through vacuum carburizing equipment.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
07.30.-t Vacuum apparatus

Abstract: Production electron-beam-welding equipment

Fred H. Samuelson

J. Vac. Sci. Technol. 11, 1109 (1974); http://dx.doi.org/10.1116/1.1318688 (1 page)

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Design considerations for production electron-beam equipment, such as power level, filament lifetime, improved beam characteristics, and stability of beam location are briefly reviewed. The main features and requirements of three types of electron-beam-welding systems (partial vacuum, nonvacuum, and high vacuum) developed by Hamilton Standard are described in detail. Of particular note is their telefocus electron gun which is claimed to provide focus control that is independent of beam current.
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81.20.Vj Joining; welding

Vacuum sintering of stainless steel

George Otto

J. Vac. Sci. Technol. 11, 1110 (1974); http://dx.doi.org/10.1116/1.1318689 (4 pages)

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The vacuum-sintering operation at The Maytag Company is discussed in detail; work with several types of stainless steels is described. The focus is chiefly on type 304-L, since the bulk of Maytag’s experience has been with this material. A typical vacuum-sintering cycle is also described. Photomicrographs showing normal and abnormal microstructures of as-sintered 304 stainless, as well as the microstructure of 410 stainless with carbon additions are summarized.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Bx Metals, semimetals, and alloys

Space-related composite-material experiments

S. Kaye

J. Vac. Sci. Technol. 11, 1114 (1974); http://dx.doi.org/10.1116/1.1318690 (4 pages) | Cited 4 times

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The preparation of composites in space depends on the immersion of reinforcements in a liquid-metal matrix and their uniform, stable dispersion in the bulk products until solidification occurs. The chief problem in achieving the composite is associated with the “wetting” of the reinforcements. A study of the theory of wetting revealed that wetting is prevented by the presence of gaseous and oxide contaminants at the interface between the pure liquid and pure solid. Experiment then confirmed that the use of a vacuum environment, cleaning of all surfaces, elevated temperature, ion bombardment, and vigorous mechanical agitation enabled the immersion and dispersion of candidate reinforcements. The technique is limited by the increased tendency for reaction if the time at elevated temperature is extended.
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81.10.Mx Growth in microgravity environments
81.20.-n Methods of materials synthesis and materials processing

Highly undercooled alloys: Structure and properties

T. Z. Kattamis and R. Mehrabian

J. Vac. Sci. Technol. 11, 1118 (1974); http://dx.doi.org/10.1116/1.1318691 (5 pages) | Cited 8 times

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Iron, nickel, and cobalt-base alloy melts can undercool by reproducible amounts, up to approximately 300 °C, prior to nucleation of the solid, provided that high-purity materials are used, and metling and solidification are conducted in vacuum or under reduced inert atmosphere, using crucibles made of amorphous materials (fused silica) or crystalline crucibles (alumina) coated with a fluid glass slag. Highly undercooled alloys exhibit microstructural uniformity and compositional homogeneity. With increasing amount of undercooling, the dendrite morphology, and hence the microsegregation pattern, change drastically. Beyond a critical undercooling of about 170 °C for all the alloys investigated, the grains become very fine and the dendritic growth is replaced by a spherical growth accompanied by a substantial reduction in microsegregation. Mechanical-property evaluation conducted on as-cast Ni-30% Cu and Fe-25% Ni and fully heat-treated AISI 4330 low-alloy steel and Ni-20% Cr indicated a substantial improvement of room-temperature ductility with undercooling. Typically, percent reduction in area of fully heat-treated AISI 4330 was tripled and fracture toughness was increased by about 40% by a 200 °C undercooling.
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81.05.Bx Metals, semimetals, and alloys
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Abstract: Effect of pool temperature gradients on the composition of electron-beam vapor-deposited alloys

R. C. Krutenat

J. Vac. Sci. Technol. 11, 1123 (1974); http://dx.doi.org/10.1116/1.1318692 (1 page)

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The common requirement of a water-cooled hearth for continuous electron-beam evaporation of alloys with a rod-fed source introduces a temperature gradient in the evaporating surface. A spatial heterogeneity of alloying constituents can be shown to result from evaporation in this gradient. Application of thermodynamic considerations to the equilibrium evaporation at constant rate from an alloy-rod-fed electron-beam vapor-deposition source provides an explanation of the spatial heterogeneity of alloy constituents in the vapor cloud. Consideration of these effects offers some direction for improved electron-beam gun/hearth design for utilization in vapor-deposition processing of complex alloys.
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81.05.Bx Metals, semimetals, and alloys
81.15.Jj Ion and electron beam-assisted deposition; ion plating

Thick deposits of ultrahigh-purity aluminum

R. B. Love and W. K. Bower

J. Vac. Sci. Technol. 11, 1124 (1974); http://dx.doi.org/10.1116/1.1318693 (4 pages)

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Films of ultrahigh-purity aluminum 150-μ thick were vacuum deposited on nickel ribbon as a technique for fabricating strip conductors. These films were deposited from an electron-beam gun which was mounted in an oil diffusion pumped vacuum system. Sources of film contamination were isolated analytically and the techniques used to eliminate them are described and verified analytically.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Abstract: High-rate physical vapor deposition of refractory metals

Max A. Sherman, Rointan F. Bunshah, and Harry A. Beale

J. Vac. Sci. Technol. 11, 1128 (1974); http://dx.doi.org/10.1116/1.1318694 (1 page)

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Molybdenum, niobium, and vanadium bulk deposits produced by high-rate physical-vapor-deposition techniques (HRPVD) were characterized by impurity content, grain size and morphology, yield strength, hardness, and bend ductility. Yield strengths of molybdenum and niobium were comparable to those of wrought material having equivalent grain sizes, when the yield strength of vapor-deposited vanadium was superior to that of wrought vanadium because of its ultrafine (0.7 μ) grain size. Ultrafine-grained refractory metals, such as the vanadium deposits produced in this study, may greatly reduce void formation and growth which causes dimensional changes and degradation of mechanical properties in reactor structural components, by removing excess vacancies (produced by the neutron irradiation). For the vanadium of this study, at a typical operating temperature of a controlled thermonuclear reactor first wall (973 K), calculations show that up to 92% of the excess vacancies can be trapped at the boundaries for a dislocation density of 108 cm−2. It is suggested that HRPVD techniques may be used to prepare fine-grained materials having superior resistance to swelling induced by fast-neutron irradiation.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Bx Metals, semimetals, and alloys

A technique for the vacuum deposition of alkali metals

W. Y. Shiu, S. L. Ezer, D. J. Young, B. Rao, and M. J. Dignam

J. Vac. Sci. Technol. 11, 1131 (1974); http://dx.doi.org/10.1116/1.1318695 (2 pages)

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An ultrahigh vacuum technique for the evaporation of sodium and potassium is described. Metal ions are generated within a gaseous plasma. These migrate through the glass envelope containing the plasma, are then discharged at a gold or platinum film cathode deposited on the far side of the envelope, and enter the vacuum space as a gas. Design and operating characteristics of several units are presented.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.05.Bx Metals, semimetals, and alloys

The effects of preadsorbed oxygen contaminant on the adsorption of Al on Si (111)

J. J. Bellina

J. Vac. Sci. Technol. 11, 1133 (1974); http://dx.doi.org/10.1116/1.1318696 (8 pages)

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The effects of preadsorbed oxygen on the ordering of aluminum atoms deposited upon the (111) surface of silicon single crystals were investigated by low-energy electron diffraction and Auger electron spectroscopy. The extent of ordering of the Al atoms and the orientation of the adsorbate relative to the Si lattice were determined as functions of temperature from 200 to 1000 °C. Deposition of Al upon clean Si (111) at 25 °C produced a partially ordered Al (111) adlayer, whereas deposition upon an oxygen-contaminated surface resulted in the formation of a completely disordered Al layer. Upon subsequent heating to higher temperatures, the adlayer irreversibly converted to an epitaxial (111) films. The temperature for epitaxy was higher for increased oxygen preexposure. The results indicated that this conversion was not caused by oxygen desorption or the formation of an oxide phase.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology

The influence of vacuum specific time constants on thermal desorption experiments

D. Edwards

J. Vac. Sci. Technol. 11, 1141 (1974); http://dx.doi.org/10.1116/1.1318697 (3 pages) | Cited 1 time

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A method is described in which the temperature shift in the maxima of thermal desorption transients due to vacuum-related effects can be evaluated. Is is applied to finite pumping speed and finite conductance corrections to the desorption peak temperatures. Particularly simple expressions are found for the temperature shift in lowest order and are seen to be applicable whenever the measured desorption transient (p or dp∕dt) closely approximates the sample desorption rate (dns∕dt).
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Controlled rf-sputter etching using atomic absorption spectroscopy

H. J. Bauer and E. H. Bogardus

J. Vac. Sci. Technol. 11, 1144 (1974); http://dx.doi.org/10.1116/1.1318698 (4 pages) | Cited 1 time

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An apparatus is described based on the principle of atomic absorption spectroscopy to monitor the removal of metallic layers in an argon glow discharge. The apparatus is shown to be particularly advantageous for rf-sputter etching process control of composite metal films, such as in pattern formation for semiconductor device interconnection. Experimental results of the monitoring of the chromium removal while sputter etching CrAgCr “sandwich” films are presented.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Single-source evaporation of gadolinium-cobalt alloys

R. C. Taylor

J. Vac. Sci. Technol. 11, 1148 (1974); http://dx.doi.org/10.1116/1.1318699 (3 pages) | Cited 1 time

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A study was made of the feasibility of using single-source electron gun evaporation for the preparation of amorphous Gd-Co alloy films. The sources used covered the compositional range from Gd0.20Co0.80 to Gd0.60Co0.40. The films deposited from each source were analyzed and the results compared with those expected for ideal alloys based on calculations using Raoult's law and Langmuir's equation. It was found that real alloys gave films with compositional gradients more than twice as severe as would be expected from ideal alloy calculations. In order to obtain films with compositional variations of one percent or less, the evaporation must consume no more than one percent of the source material.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.Nq Composition and phase identification

Higher zones of stability for the quadrupole mass filter

P. H. Dawson

J. Vac. Sci. Technol. 11, 1151 (1974); http://dx.doi.org/10.1116/1.1318700 (3 pages) | Cited 4 times

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Matrix methods based on phase-space dynamics are used to examine the feasibility of operating a quadrupole mass filter using one of the higher zones of stability. Ion transmission efficiencies are calculated for various modes of operation. By using lower rf, performance may approach that of the conventional mass filter under certain conditions, but instrument apertures are generally somewhat smaller.
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07.75.+h Mass spectrometers

A new approach for computing diode sputter-ion pump characteristics

H. Hartwig and J. S. Kouptsidis

J. Vac. Sci. Technol. 11, 1154 (1974); http://dx.doi.org/10.1116/1.1318701 (6 pages) | Cited 7 times

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By using theoretical considerations combined with experimental results, a general approach for computing sputter-ion pump characteristics is given. This approach can be successfully applied to optimal design of distributed sputter-ion pumps in high energy accelerators. The deviation between computed and measured pumping speed values is less than 30%.
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07.30.Cy Vacuum pumps

A miniature extractor gauge for the UHV

D. Blechschmidt

J. Vac. Sci. Technol. 11, 1160 (1974); http://dx.doi.org/10.1116/1.1318702 (6 pages) | Cited 1 time

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The design and performance of a miniaturized hot filament ionization pressure gauge, specially developed for the CERN intersecting storage rings, is described. It is mounted on a standard metal flange with ceramic feedthroughs and fits into an aperture of 15.7 mm. The gauge is of the extractor type and has a sensitivity factor for nitrogen of about 5 Torr−1. Its low pressure limit, about 5×10−12 Torr nitrogen equivalent, is mainly due to x rays. These two characteristic figures have been obtained, in spite of the gauge's smallness, by an optimization of most of the geometrical and electronical parameters. Some problems, seriously affecting the gauge’s performance, and particularly arising from its size, such as space charge effects and thermal outgassing, are discussed.
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07.30.Dz Vacuum gauges
29.20.db Storage rings and colliders

Ultrahigh vacuum system for the study of the mechanical and electrical properties of metallic surfaces

Robert E. Cuthrell

J. Vac. Sci. Technol. 11, 1166 (1974); http://dx.doi.org/10.1116/1.1318703 (4 pages) | Cited 2 times

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A bakeable ultrahigh vacuum system was constructed for the study of the mechanics of deformation, contact resistance, bonding, friction, and high-resolution topography of metallic surfaces in contact. The instrument consists of a work chamber which is isolated from building vibrations and in which metallic samples may be cleaned by sputtering, annealed by electron bombardment, and brought together with precise control of mechanical and environmental variables. Facilities are provided for load and contact resistance measurements. A laser interference fringe microscope, which is mounted in the work chamber, is used for quantitative surface topography determinations and the measurement of load-bearing areas. This system has been used for electrical contact and solid-phase bonding studies.
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07.30.Kf Vacuum chambers, auxiliary apparatus, and materials
73.40.Cg Contact resistance, contact potential
68.35.Gy Mechanical properties; surface strains

The effect of magnetic fields on substrate temperature and film texture in an rf sputtering system

E. L. Paradis

J. Vac. Sci. Technol. 11, 1170 (1974); http://dx.doi.org/10.1116/1.1318704 (7 pages) | Cited 1 time

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Data are presented which show that the substrate temperature in a sputtering system can be greatly affected by the shape and strength of an imposed magnetic field. Deposition rate, thickness uniformity, and surface texture of the film are also affected by the fields. A sputtering system is described in which low substrate heating, uniform deposition over a reasonable area, and smooth film growth are simultaneously achieved with a particular magnetic field configuration. The role of the magnetic field is discussed.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Low-voltage triode sputtering and backsputtering with a confined plasma: Part IV. Heat transfer characteristics

B. E. Nevis and T. C. Tisone

J. Vac. Sci. Technol. 11, 1177 (1974); http://dx.doi.org/10.1116/1.1318705 (9 pages) | Cited 1 time

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A theoretical and experimental investigation of the heat transfer processes encountered in sputtering and backsputtering systems have led to a method of cooling which does not involve clamping a wafer or substrate to a liquid cooled holder. The basic philosophy of the new method is to take full advantage of radiative cooling of the wafer by: (a) designing the holder so that the wafer has an unobstructed view of the water-cooled bell jar and is thermally isolated from the holder; (b) increasing the emittance of the side of the wafer facing the bell jar by the application of a black body coating. In addition to the above two modes, it is shown that tilting the wafer from a horizontal plane up to 45 °, although introduced primarily to reduce step problems, results in a decreased heating rate and subsequent lower wafer temperatures. Whether one would use one, two, or all three modes depends upon the heating rate (sputtering or backsputtering level), and the maximum temperature the wafer could stand without device damage. For example, if one does not wish to exceed 250 °C in a backsputtered silicon wafer, and at the same time it is desired to maximize the backsputtering rate, then, by employing a properly designed holder, tilted at 45 ° with the top side of the silicon of a black body, one could backsputter at a level corresponding to a heating rate of 0.6 W∕ cm2. This corresponds, conservatively, to a removal rate of gold of 2500 Å∕min. Design curves are presented which permit the prediction of steady state silicon wafer temperatures as a function of heat rate and silicon top side emittance. These theoretical predictions are corroborated by experiments. This study indicates that much of the present sputtering and backsputtering of silicon wafers can be accomplished without clamping the wafer to a liquid-cooled holder.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
44.10.+i Heat conduction

Nodular growth in thick-sputtered metallic coatings

T. Spalvins and W. A. Brainard

J. Vac. Sci. Technol. 11, 1186 (1974); http://dx.doi.org/10.1116/1.1318706 (7 pages) | Cited 10 times

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Thick-sputtered S-Monel, silver, and 304 stainless steel coatings were deposited on mica and metal substrates with various surface finishes to investigate the nodular growth in the coating by scanning electron microscopy. The geometry and the surface structure of the nodules are characterized. Compositional changes within the coating were analyzed by energy dispersive x-ray analysis. Defects in the surface finish (i.e., scratches, inclusions, etc.), act as preferential nucleation sites and form isolated and complex nodules and various surface overgrowths in the coating. The nodule boundaries are very vulnerable to chemical etching and these nodules do not disappear after full annealing. Further, they have undesirable effects on mechanical properties; cracks are initiated at the nodules when the coating is stressed by mechanical forces. These effects are illustrated by micrographs. Nodular growth within a coating can be minimized or eliminated by increasing the surface smoothness.
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81.05.Bx Metals, semimetals, and alloys
81.15.Cd Deposition by sputtering

Relative work function of clean molybdenum single-crystal planes determined by field emission microscopy

G. Bergeret, M. Abon, B. Tardy, and S. J. Teichner

J. Vac. Sci. Technol. 11, 1193 (1974); http://dx.doi.org/10.1116/1.1318707 (2 pages)

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A probe-hole field emission microscope has been used to determine the work function of clean molybdenum single crystal planes relative to the average work function of the field emitter, assumed to be 4.20 eV. Results obtained are compared with other available data. (AIP)
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.37.Vj Field emission and field-ion microscopy

A device for making electronmicroscopic replicas of annealed hygroscopic crystal surfaces

D. Knoppik and H.-Ch. Bartscherer

J. Vac. Sci. Technol. 11, 1195 (1974); http://dx.doi.org/10.1116/1.1318708 (1 page)

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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
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