Ag Si Research Articles

Measurement of Sputtering Rate for 10 keV O2+ Ions with Ion Microanalyzer

The sputtering rates of single-crystal Si and polycrystalline Ag, Cu, Ni and Al were measured. The target materials were bombarded with oxygen ions accelerated at 10 kV. The sputtering rates of the target materials were a fifth of those obtained with an argon ion beam. The difference was larger than the difference between the masses of the oxygen and argon ions used for the incident beams. However, the sputtering rates with oxygen ions were related to the strenght of the bonds between the atams of the target material by the following expression, from analogy with an argon ion beam. Sr=4(I/D)(Ec/Mt)-1.4, where Sr is the sputtering rate, I is the current density of the incident ions, and D, Mt and Ec are the atomic density, mass number and cohesive energy of the target material, respectively.

Ion-beam mixing of metal-semiconductor eutectic systems

A study has been made of the ion-beam mixing of four metal-semiconductor eutectic systems (AuSi, AuGe, AlGe and AgSi). Two sample configurations were used: (1) unlimited supply where a single metal layer was deposited on a semiconductor substrate, and (2) limited supply where multiple layers of metal and semiconductor of a fixed composition were deposited onto an inert substrate. Inert gas ions were used to cause mixing between the metal and semiconductor. The ion-beam mixing behavior of the four systems can be categorized into two groups.For AuSi and AuGe (group A), the mixing is efficient. For Al-Ge and AgSi (group B), the mixing is much less compared with that of the group A systems. In the case of samples with an unlimited supply configuration, group A systems exhibited a mixed layer of well-defined composition (Au 71Si 29 and Au 50Ge 50) which is formed initially at the metal-semiconductor interface. The thickness of the mixed layer increases with the square root of the ion dose. The structure of the mixed layer is metastable in nature. The efficiecy of mixing and the uniformity of the mixed layer improve with an increase in the substrate temperature from cryogenic to room temperatures. For group B systems, the mixing is limited to the interfacial regions even at elevated substrate tempertures (up to ∼ 200°C). At higher substrate temperatures, solid-phase reactions (similar to solid-phase epitaxial growth) take place even without the influence of an ion beam. In the case of multiple layered samples (limited supply), mixing is pronounced for group A systems. For group B systems, relatively uniform mixed layers can be obtained if the individual layer thickness is similar to the interfacial concentration spread caused by ion beams in samples with a single deposited metal layer (unlimited supply configuration). These results are compared with those obtained by laser melting aand quenching experiments as well as splat-cooling experiments.

Ion-beam-induced reactions in metal-semiconductor and metal-metal thin film structures

Ion-induced reactions in thin film systems have been used to form equilibrium and metastable compounds, amorphous layers, and solid solutions. Samples were prepared by depositing metal films on Si or Ge substrates or by depositing multiple-layer films on inert substrates. Ar, Kr, or Xe ions at energies between 100 and 300 keV and dose of a few times 10 15 ions/cm 2 were used. In compound-forming systems, such as silicides, where chemical driving forces are significant, the substrate temperature during ion bombardment plays an important role. At substrate temperatures above 25–50°C, equilibrium phases are generally formed at growth rates that depend strongly on substrate temperature. At lower temperatures, intermixed layers are formed; the thickness of the layers is relatively insensitive to temperature. In both temperature regimes, the thickness of the intermixed layer depends on ion dose and species. In AuSi and AuGe eutectic systems, metastable phases were formed. With AgSi and AlGe eutectic systems, only limited intermixing was found. In metal-metal systems, solids solutions of extended solubility have been formed. Single-phase fcc solid solutions were formed across the entire composition range of AgCu and AuCo multiple-layer structures. With heat treatment, the single-phase solutions transform to equilibrium two-phase mixture. In near-immiscible systems, such as AgNi, an extension of the solubities was found. In general, ion-beam mixing provides a wider range of composition of solid solutions that can be obtained by splat-cooling or high dose plantation.

Ion bombardment induced interface mixing in the AgSi system

High resolution Rutherford backscattering has been used to investigate the ion-beam-induced intermixing of silver films deposited onto silicon under increasing fluences of 40 keV Ar + ions. The onset of atomic mixing in the interface occurs when the Ag layer has been sputtered down to about 300 A ̊ (∼ R p + ΔR p for 40 keV Ar +→ Ag ). The composition in the mixed layer varies in a uniform, almost linear way, and the layer spreads laterally with increasing fluences towards a constant value. There is no evidence for the formation of regions of specific composition, in contrast to other Simetal systems (e.g. SiPt, SiPd, SiAu). For higher doses, the amount of Ag remaining decays more or less exponentially. The width of the mixed layer and the exponential decay of residual Ag are shown to correspond reasonably with theoretical predictions of atomic mixing processes.

Electronic and atomic structure of Si(111) Al, Ag, and Ni metal overlayer induced surface reconstructions

The electronic structure of the ordered metal overlayers Si(111) √3× √3: Al and √3×√3: Ag and Si(111) √19×√19: Ni prepared from Si(111)7×7 surfaces has been studied with angle-resolved photoelectron spectroscopy. On all these surfaces we find dangling bond derived bands which for Al and Ag overlayers have a dispersion of 0.4 eV. We also report a new Si(111) √7×√7: Al structure at ?0.5 monolayer coverage of Al. A new structural model for the √19×√19: Ni surface is proposed.

Estimation of sputtering rate by bombardment with argon gas ions

The sputtering rates of single-crystal Si and polycrystalline Ag, Cu, Ni, Ti, and Al were measured. These target materials were bombarded with argon ions accelerated at 10 kV. The sputtered depth after a given interval of bombardment was greatest for Ag, and decreased for the other materials in the following order: Cu, Ni, Ti, Si, and Al. The difference in the sputtering rates of these target materials was investigated on the basis of their binding energies, and the following expression for sputtering rate was obtained experimentally, Sr=K (I/D)(M/Ec)k, where Sr is the sputtering rate, I is the current density of incident argon ions, and D, M, and Ec are the atomic concentration, mass number, and cohesive energy of a target material, respectively. K and k are constants. Sputtering yield (Sy) can be written Sy=K′ (M/Ec)k. The result was compared with experimental data of many target materials already reported. These results were used to estimate the sputtered depth after a given interval in the practical analyses using ion bombardment.

Characterization of the interface states at a Ag/Si interface from capacitance measurements

From the variation of the quasi-Fermi levels at the interface of a Ag–Si diode under forward bias, we present a new way to characterize the interface states of such an interface from capacitance and conductance measurement. We obtained the density, the time constant, and the capture cross section of the interface states. The relative energy distribution of the interface states is in close agreement with those deduced from our photoelectric measurements. Such a determination implies that interface states are in equilibrium with silicon, in agreement with Heine's theory.

A study by X-ray diffraction of the deformation of AGSI alloys

Abstract : The deformation of two-phase Ag-Si alloys has been studied by X-ray line broadening. Equiaxed and needle Si morphologies were examined. The Si particles do not deform. The dislocation densities in the Ag matrix are higher with the needle morphology, in agreement with Ashby's predictions. (Author)

Generation of chemical potentials by analysis of phase diagrams part III: Eutectic systems

The method of determination of thermodynamic properties of alloys from phase equilibria data 1 is extended and applied to several different types of eutectic systems: AgSi, AgCu, CdZn and PbSn. Good agreement with experimental data (when available) is shown in all cases.

Appraisal of semiconductor-metal-semiconductor transistor

This paper considers the basic limitations of a semiconductor-metal-semiconductor transistor (SMST) and evaluates its performance in practical microwave circuits. The low frequency common-base current gain α 0 for SiAuGe and SiAgGe transistors is about 0.3. Discussion is presented suggesting that it is unlikely that materials combinations exist capable of substantially higher α 0. Thus the transistor shows current loss and can attain power gain only by means of impedance gain. In coaxial-line and waveguide structures both high and low impedance levels require very small mechanical dimensions and tolerances. With present technology, attainable impedance ratios appear to be limited to about 100. The technological problems associated with the fabrication of the SMST are discussed. The greatest obstacle is the deposition of device-quality semiconductor material on thin metal films. For a SiAuGe structure with a collector epitaxial layer 1 μ thick, base-metal thickness of 100 Å, emitter stripe width of 1 μ, and at a current density of 3000 A/cm 2, the calculated values at 10 GHz are: 26 db for the unilateral gain, 29 db for the maximum stable gain with a resistance ratio of 10 4 and about 10 db for the transducer gain with a stripe length of 1000 μ and a resistance ratio of 100, where no parasitic losses were included in the above figures and optimum adjustments were assumed for reactive components of generator and load immitances. For an α 0 of 0.3 the minimum noise figure in an SMST is 7.9 db.