A comparison of the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics of thermal and low temperature ion beam grown films of silicon oxide was made. The oxides were in the thickness range between 5 nm and 10 nm. The ion beam oxides were grown at room temperature. The bulk resistivities of the thermal oxides were about 1017 ohm cm and were about 5 orders of magnitude lower for the ion beam oxides. The interface charge densities at the Si-SiO2 interface were about an order of magnitude higher in the case of the ion beam oxides. The oxide properties were also measured after current stressing at constant voltages. The thermal oxides showed an increase in the interface trap density at the Si-SiO2 interface after stressing with a distinct trap appearing above mid-gap. The ion beam oxides showed very little increase in the interface trap density after stressing. The higher conductivity of the ion beam oxides may have lead to discharging of the interface traps generated during stressing.

Silicon wafers with and without protective1Ahermil oxide were implanted with oxygen at 150keV with doses 1.6 – 2.0×1018 cm−2. Transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) were used to study the top silicon layer remaining above the implanted buried oxide. regular array of spheroidal voids filled with oxygen gas was observed only in the samples that were not protected by the oxide. The voids were aligned into individual columns whose crystallographic orientation with respect to the host silicon lattice matched the direction of the implantation. The origin and the kinetics of their formation are discussed.

We review and discuss the main structural phenomena inherent in epitaxial multilayer semiconductor growth: lattice mismatch, misfit dislocation generation, two-dimensional vs. threedimensional growth, interface abruptness and planarity and the local atomic structure of semiconductor alloys. The prevalence of metastable structures, often a function of crystal growth temperature, is discussed. We also investigate the effect of Si ion implantation and subsequent rapid thermal annealing of AlGaAs/GaAs and InGaAs/GaAs multilayer structures, with reference to strain relaxation, layer planarity and enhanced Al, In and Si diffusion.

Subsequent to the implantation of certain ions, the thermal stability of AlGaAs/GaAs superlattices can be reduced, enabling mixing of the layers at temperatures where they would otherwise be stable. The mixed layers have intermediate alloy composition and are of good crystalline quality. As a result this process is of great value in device fabrication where a high degree of vertical and lateral bandgap control is desirable. This paper reviews our work in understanding the mechanism of diffusion, its dependence on varilous process parameters, and potential applications in device fabrication.

We have characterized damage production in both (InGa)As/GaAs and Ga(AsP)/GaP strained-layer superlattices for silicon implants at 80 K, 300 K or 673 K at fluences sufficient to induce compositional disordering of the superlattice layers. Implants at low temperatures (80 K for the (InGa)As/GaAs system, 300 K and below in the Ca(AsP)/GaP system) are characterized by well-defined amorphous layers at depths consistent with the predictions of ion range codes. Implants at higher temperatures are characterized by greatly reduced damage levels with substantial densities of extended defects located near the mean ion range. Point defect clusters are preferentially located in the ternary layers in the (InGa)As/GaAs SLS at the deepest part of the implanted zone. Despite the absence of amorphous layer formation, precipitous stress relief still occurs for the Si-implanted (InGa)As/GaAs SLS.

The interdiffusion mechanism in Hg(l-x)X(x)Te/CdTe superlattices where X is Cd, Mn, or Zn can be deduced from the magnitude of the interdiffusion activation energy. By comparing in-situ x-ray diffraction measurements (our work) with results from Tang and Stevenson (J. Vac. Sci. Technol. AS, 1987), it is found that anionic and cationic Frenkel pairs represent the most likely interdiffusion mechanism in Hg(l-x)X(x)Te/CdTe superlattices. This model mixes vacancies and interstitials, as well as maintaining the conduction type and the electronic mobility. It is further shown that interdiffusion sets in as soon as the growth starts.

In the most commonly used form of ellipsometry, a monochromatic collimated linearly polarized light beam is directed at an angle φ to the normal of a sample under study. The specularly reflected beam is, in general, elliptically polarized, and the state of polarization is analyzed using a second polarizer and photodetector.1 Figure 1 shows a schematic of the rotating analyzer automated spectroscopic ellipsometer used at the University of Nebraska. The angle of incidence can be set over a wide range of angles, with a precision and repeatability of ±0.01 angular degrees. A computer controls the monochromator, the azimuth of a stepper motor driven polarizer, a shutter, and the digitization of the detector signal. There are several other schemes used for acquiring ellipsometric data, and these are discussed in several sources.

Bilayer samples of Ti/C and Fe/C have been ion beam mixed with 400 keV Xe ions to a dose of 1 × 1016 ions/cm2. Mixing experiments were performed at 77, 300, 573, and 723 K. The transition between the temperature independent and temperature dependent mixing occurred between 300 and 573 K in Fe/C samples and between 573 and 723 in Ti/C sample. In the temperature independent mixing regime mixing is reasonably well explained by a thermodynamic model of ion mixing while at higher temperatures a radiation enhanced diffusion mechanism is evident.

Ion mixing experiments using Xe ions at temperatures ranging from 77K to about 450K were conducted on Al/Ni and Al/Pt couples. Evaporated polycrystalline Al films and large-grained Al crystals were used as substrates. Xenon irradiation of Al/Pt bilayers achieves considerable intermixing and a temperature dependence is observed. Only moderate interfacial mixing with little temperature dependence is observed in Al/Ni bilayers. The mixing efficiency of Al/Ni is consistent with the phenomenological model of thermal spike mixing, and so is the absence of a pronounced temperature dependence below 450K. No significant difference is noted in ion mixing of evaporated and large-grained Al substrates. In contrast to ion mixing, Al/Pt and Al/Ni samples behave similarly upon thermal annealing and form well-defined compounds. The results are also compared with Si/metal systems, where silicides can be formed readily by low temperature thermal annealing as well as by ion mixing of bilayer samples.

Multi-layered films of Ti-Au of linearly varying composition were produced by ion irradiation using 600 KeV Ar++ ions. Rutherford Backscattering Spectrometry showed that mixing was complete. The microstructure observed by transmission electron microscopy consisted of a combination of crystalline and amorphous phases at the Ti-rich end and of a crystalline fcc Au solid solution at the Au-rich end. Corrosion testing in a simple immersion cell revealed remarkable corrosion resistance of the ion beam mixed sample compared to that of pure titanium or as-deposited Ti-Au samples (from 100%Au to 60%Ti-40%Au). Wear and friction testing was performed using a reciprocal sliding apparatus with a polytetrafluoroethylene (PTFE) pin. A composition of 60%Ti-40%Au was chosen as optimal for improved corrosion resistance without appreciable degradation in wear and friction properties.

The relationship between growth rate of CrSi2 and dose rate during Xe ion irradiation at 500K is investigated. Dose raies difffering by up to a factor of 40 have been utilized to study the relationship. For a fixed total dose, a lower dose rate results in a thicker silicide layer compound to a higher dose rate. The results are explained from radiation-enhanced diffusion theory.

A low-energy ion beam deposition system has been developed at Oak Ridge National Laboratory and has been applied successfully to the growth of epitaxial films at low temperatures for a number of different elements. The deposition system utilizes the ion source and optics of a commercial ion implantation accelerator. The 35 keV mass- and energy-analyzed ion beam from the accelerator is decelerated in a four-element electrostatic lens assembly to energies between 10 and 500 eV for direct deposition onto a target under UHV conditions. Current densities on the order of 10 A/cm are achieved with good uniformity over a 1.4 cm diameter spot. The completed films are characterized by Rutherford backscattering, ion channeling, cross-section transmission electron microscopy, and x-ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning have been studied. Epitaxial overlayers which show good minimum yields by ion channeling (3–4%) have been produced at temperatures as low as 375°C for Si on Si(100) and 250°C for Ge on Ge(100) at growth rates that exceed the solid-phase epitaxy rates at these temperatures by more than an order of magnitude.

Our experiments show that ionized cluster beams (ICB) can form epitaxial Al films on Si(111) and Si(100) substrates. This is unique because the lattice misfit of this material combination is more than 25%. Al can also be epitaxially grown on CaF2 films deposited on Si substrates. The initial stage of the film formation is measured by in-situ electron diffraction. In the case of Al(111) growth on Si(111) and CaF2, growth of mixed layers of different epitaxial islands of approximately 20–50 Angstrom thickness on the substrate surface is observed. With increase of thickness, the film shows the single crystal state with a flat surface, which indicates the epitaxial single crystal film formation on CaF2 or on Si substrates. It should be noted that in the Al/CaF2/Si (MIS) structure, the epitaxial CaF2 is a good insulating layer, which can be used to prepare three dimensional devices. These results show that the kinetic energy and the ionic charge of cluster ions have much influence on surface and interface modification, and that ICB is capable of producing films of good quality at low substrate temperatures.

The distribution of charged gold clusters and micro droplets emitted from liquid gold ion source as a function of charge to mass ratio has been investigated using three complementary techniques: transverse magnetic deflection, quadrupole mass spectrometry, and single particle detection scheme. The measurements have been made as a function of total beam current and angle of emission. The above three methods have some overlap range that was used for comparison and verification of data gathered by each technique. The magnetic deflection results indicate that for the source structure used in this study, clusters are present along the axis of the beam, over the entire current range under investigation. However, their relative abundance is significantly increased as total current is increased. The quadrupole data exhibits a broad peak which is centered around 104 Coul/Kg corresponding to a cluster of ≈ 1000 atoms charged to ≈20+. The position of the peak moves slightly toward lower mass (higher Q/m ratio) as the total beam current is increased. The biggest cluster detected so far using single particle detector has a charge to mass ratio of 17 Coulomb/Kg corresponding to a droplet of 108 Au atoms having a radius of ≈ 740Å atoms charged to ≈ 9000+. Several experimental observations point to the fact that cluster dominated emission mode might be qualitatively different from ion emission mode. Based on experimental observations a qualitative model for cluster emission is proposed.

We report an investigation of Al films deposited on Si(100) surfaces by a partially ionized beam. By controlling the Al ion to atom ratio in the beam and the bias potential applied to the substrate, two different orientations, namely, the Al(110) and the Al(111) faces, can be formed on the Si(100) substrate.

If the thermal adatom mobility is limited during film growth, the kinetic energy delivered to the film surface by arriving species is the key parameter which determines the resulting film microstructure and properties. Kinetic models and growth simulations of nonequilibrium film growth have been used to study the influence of incident kinetic energy of adatoms and energetic ions on the film microstructure, microporosity, density, stoichiometry and epitaxy. Deposition processes like vapor, sputter, ion-assisted and ionized cluster beam deposition, could be examined in detail with particular emphasis on optical coatings. The theoretical descriptions used are based on the solid-gas, thermal spike, collision cascade and molecular dynamics model.

The properties of plasmas generated by the interaction of a pulsed CO2 laser with several solid evaporation targets were studied and the films deposited from such plasmas were characterized. A large flux (˜ 1014/cm2/s) of ions at high velocities (2 − 10 × 106 cm/s) was measured in these plasmas. ZrO2 thin films deposited by laser-assisted evaporation on room temperature substrates had crystalline-oriented structures. Low optical absorption and high refractive index values (2.15 at 632.8 nm) indicated the stoichiometric and dense nature of these films.

The implantation of Ti into LiNbO3 has been studied as a means of altering the optical index of refraction to produce optical waveguides. Implanting 2 × 1017 atoms/cm2 of 360-keV Ti at liquid nitrogen temperature produces a highly damaged region extending to a depth of about 4000 Å. Solid-phase epitaxial regrowth of the LiNbO3 can be achieved by annealing in a water-saturated oxygen atmosphere at 400°C, though complete removal of the residual damage usually requires temperatures in excess of 800°C. The solid-phase epitaxial regrowth rate exhibits an activation energy of 2 eV at doses below 3 × 1016 Ti/cm2, but both the regrowth rate and activation energy decrease at higher doses. At doses above 1 × 1017 Ti/cm2, the solid-phase epitaxial regrowth occurs only at temperatures above 800°C.

Conventional chemical vapor deposition (CVD) has historically utilized high melting temperature substrates. Recently there has been an increased desire to coat temperaturesensitive materials such as aluminum, glass, steel, and even plastic. Thus “cold” CVDprocesses, most using plasma excitation, have been developed. In these processes gas molecules or atoms are excited by dc or ac glow discharge, thereby allowing the possibility of keeping substrates at room temperature.

This paper describes plasma CVD reactors using capacitive coupling of r.f. voltage to an asymmetrical arrangement of electrodes. Using organic or metal-organic process gases and mixtures of them with inorganic gases, deposition takes place on the reactor walls, the anode, and the cathode. In this paper the emphasis is on deposition on negatively selfbiased substrate holders. Physical and chemical properties of plasma-CVD grown layers depend on about six process parameters, the most important of which are cathode voltage, gas pressure, choice of gases, and mixing ratio of gases. Map-like representations show the dependence of coating properties on deposition parameters. Layer materials discussed include amorphous hydrogenated carbon (a-C:H). WCx, SiOx:H, SiCxOy:H. and SnOx:H.

Aluminum nitride thin films have been deposited by ion-assisted deposition. Aluminum was electron-beam evaporated onto substrates with simultaneous nitrogen ion bombardment. Rutherford backscattering spectrometry showed that nitrogen-to-aluminum ratios of one or greater could be achieved with sufficient nitrogen ion fluxes. This excess nitrogen apparently degrades the optical properties of the films in the visible. Annealing at 500°C improves the optical properties drastically at the expense of a slight oxygen diffusion into the films. Finally, aluminum oxynitride films were deposited by adding an oxygen backfill to the vacuum chamber during deposition. These films had very similar optical properties to the annealed nitride films.