Menachem Nathan

Epitaxial films of semiconducting FeSi2 on (001) silicon

Epitaxial thin films of the semiconducting transition metal silicide, beta‐FeSi2, were grown on (001) silicon wafers. The observed matching face relationship is FeSi2(100)/Si(001), with the azimuthal orientation being FeSi2[010]‖‖Si〈110〉. This heteroepitaxial relationship has a common unit mesh of 59 A2 area, with a mismatch of 2.1%. There is a strong tendency toward island formation within this heteroepitaxial system.

Granular Fe in a metallic matrix

Ultrafine Fe particles with coercivities in excess of 500 Oe have been obtained by rapid annealing of sputtered metastable FexCu1−x alloys. The enhanced magnetic properties of these phase‐separated materials are typical of single‐domain Fe grains, and can be controlled by the annealing temperature. The Cu matrix, however, is highly conducting, unlike conventional granular materials where the matrix is generally insulating. The evolution of the magnetic properties and microstructure during annealing are described.

Epitaxial orientation and morphology of β‐FeSi2 on (001) silicon

Epitaxially aligned films of β‐FeSi2 were grown on (001) silicon by reactive deposition epitaxy (RDE), molecular‐beam epitaxy (MBE), and solid‐phase epitaxy (SPE). Although the matching crystallographic faces, FeSi2 (100)/Si(001), remained invariant throughout this study, two different azimuthal orientations predominated, depending on the deposition mode and growth temperature. Films with the FeSi2[010]∥Si〈110〉 orientation (grown by RDE at typically 500 °C) were of a genuine large‐area single‐crystal structure; however, the surface morphology was rough due to islanding which always preceeded the formation of a continuous film. Films of the alternative azimuthal orientation FeSi2[010]∥Si〈100〉 (which were grown by SPE at typically 250 °C or by MBE at temperatures as low as 200 °C on top of an SPE‐grown template) have a much smoother surface morphology. However, there was some loss of purity in the epitaxial alignment at these extremely low temperatures. Excellent RHEED (reflection high‐energy electron diffr...

On the unusual electromigration behavior of copper interconnects

The present uncertainty in the ability of Cu to substitute for Al as the conductor material in very large scale integration arises from the perplexing electromigration behavior of Cu interconnects: the electromigration activation energy in multigrained lines is often about two times lower than for grain‐boundary diffusion, while the pre‐exponential factor in the electromigration rate expression is several orders of magnitude smaller than that characteristic of electromigration along grain boundaries. Using literature data, in particular those of drift velocity experiments, we show that regardless of these unusual facts, grain boundaries are still most likely the major electromigration diffusion pathways in Cu interconnects. Based upon recent progress in the theory of grain‐boundary grooving with an arbitrary grain‐boundary flux [Klinger et al. J. Appl. Phys. 78, 3833 (1995)], and the specific model applying the general theory to electromigration [Glickman, Phys. Low‐Dim. Struct. 11/12, 69 (1994)], we expl...

SnO2 transparent conductor films produced by filtered vacuum arc deposition

Thin films of SnO2 were prepared using an Sn cathode vacuum arc deposition system, operated with a low pressure O2 atmosphere. The plasma flux emerging through an annular anode passed into a magnetized quarter torus, which bent the plasma beam, separating it from macroparticle contaminants. Within a time of 5–15s after arc ignition, the initial background pressure Pi in the system was rapidly pumped by the plasma jet to a working pressure Pw that was two orders of magnitude lower. For 4 12 mTorr, the arc pump-down time was very long and the deposition rate was very low. The films were analyzed by X-ray diffraction, transmission and scanning electron microscopy (TEM, SEM), Auger electron spectroscopy (AES), and resistivity and transparency measurements. The changes in the films under thermal treatment in vacuo and in Ar were also examined. According to the X-ray and TEM diffraction data, as-deposited films on non-heated substrates and substrates heated to 200°C consist of an amorphous phase. Crystallization of the amorphous phase prepared at Pw=6 mTorr to tetragonal SnO2 occurs at 450°C. At Pw<3 mTorr, however, the films deposited crystallize to SnO after annealing. The AES results show that the films consist of only Sn and O, and that the shape of the Sn spectra changes with the Sn oxidation states. Ar annealing and rapid thermal annealing at a temperature of 300°C decreased the resistivity of the films deposited at Pw=6 mTorr to 8 × 10−4ohms cm, while the film structure remained amorphous. These films have resistivities equivalent to the best values obtained by any method for undoped SnO2, while the deposition time is less for the same film thickness.

Ultrasensitive displacement sensing using photonic crystal waveguides

We present an ultrasensitive displacement sensor and sensing technique based on photonic crystal waveguides (PCWG), useful for integration with microelectromechanical system (MEMS) structures. The sensor consists of two PCWGs aligned along a common axis, one mounted on a moving part and the other fixed to a stationary substrate. A gap between the fixed and moving PCWGs creates an intersection with a third, perpendicular PCWG, which has two branches. The intensity exiting each PCWG changes when the suspended PCWG moves in plane relative to the fixed one. The difference in intensities exiting the two perpendicular PCWG branches can be correlated with the relative displacement between the fixed and moving PCWGs. Numerical simulations predict a sensitivity of ∼1[μm−1] using a light source of 9.02μm.

On the kinetic mechanism of grain boundary wetting in metals

The thermodynamic condition characteristic of grain boundary wetting (GBW) causes an imbalance between grain boundary (GB) and solid–liquid interphase surface tensions γGB and γSL. This creates in turn a force acting at the root of the GB groove, and pointing into the solid. The “indentation” action of this force is suggested to cause stress-driven self-diffusion into the GB. This process removes the solid atoms from the groove cavity and causes their deposition along the GB (“internal solution”). Assuming that the GB acts as a perfect sink, this “self-indentation-internal solution” mechanism can account for a number of GBW features: the non-Mullins grooving morphology and linear kinetics, the origin of the singular stress field at the wetting front, the expansion of the solid under GBW, the influence of external stress on GBW, the GBW transitions with temperature, and the fast atomic penetration of the liquid metal ahead of the groove root.

Annealing and Sb-doping of Sn—O films produced by filtered vacuum arc deposition: structure and electro-optical properties

Abstract Tin oxide films were deposited using a filtered vacuum arc at rates up to 10 nm s−1. Optimal results were obtained with a 160 A arc when the deposition pressure was in the range 6–9 mTorr. The structure of the films was amorphous if the deposition temperature, or the post-deposition annealing temperature, was less than 350°C, while films containing orthorhombic, tetragonal, and amorphous phases were obtained at higher temperatures. Annealing or substrate heating with temperatures within the amorphous range improved the conductivity considerably, and was accompanied by increases in the optical gap, carrier density, and carrier mobility. The improvements are attributed to greater short-range ordering. Annealing or substrate heating into the crystalline range yielded higher resistivity films. Sb doping did not decrease the resistivity of the amorphous films. The lowest resistivities obtained, (5–7) × 10−4ωcm, were equal to or less than any reported in the literature for undoped Sn—O films, and were obtained at deposition rates considerably higher than with other techniques.

Monolithic rare-earth doped sol-gel tapered rib waveguide laser

We report the design, fabrication, and characterization of a monolithic tapered rib waveguide laser made of Nd doped silica hafnia sol-gel. The laser has a 604nm thick guiding layer. CW pumping was coupled in via a grating which also coupled out the lasing signal output, while reflection gratings supported the feedback. A lasing threshold of 20mW and an output power of 2.45mW were measured in a 3cm long device.

Numerical simulation of grain-boundary grooving by level set method

A numerical investigation of grain-boundary grooving by means of a level set method is carried out. An idealized polycrystalline interconnect which consists of grains separated by parallel grain boundaries aligned normal to the average orientation of the surface is considered. Initially, the surface diffusion is the only physical mechanism assumed. The surface diffusion is driven by surface-curvature gradients, while a fixed surface slope and zero atomic flux are assumed at the groove root. The corresponding mathematical system is an initial boundary value problem for a two-dimensional equation of Hamilton–Jacobi type. The results obtained are in good agreement with both Mullins analytical “small-slope” solution of the linearized problem (W. W. Mullins, 1957, j. Appl. Phys. 28, 333) (for the case of an isolated grain boundary) and with the solution for a periodic array of grain boundaries (S. A. Hackney, 1988, Scripta Metall. 22, 1731). Incorporation of an electric field changes the problem to one of electromigration. Preliminary results of electromigration drift velocity simulations in copper lines are presented and discussed.