J. Gyulai

Ion‐induced amorphous and crystalline phase formation in Al/Ni, Al/Pd, and Al/Pt thin films

Amorphization by ion beam irradiation of multilayered samples of Al/Pt, Al/Pd, and Al/Ni has been investigated by selected area diffraction and Rutherford backscattering. With a dose of 2×1014 Xe ions/cm2, uniform mixing is achieved in the Al/Pt system and the amorphous phase is produced over a large composition range. In the Al/Pd and Al/Ni systems, amorphous phases or the equilibrium, crystalline phases are formed depending on the composition of the films. The same results were found when the samples were annealed to form crystalline phases before bombardment. For thin films of these fcc metals, only the simplest intermetallics, NiAl and PdAl, (primitive cubic structures with 2 atoms/cell) were formed in crystalline form by ion‐beam irradiation.

Kinetics of TiSi2 formation by thin Ti films on Si

Silicide formation with Ti deposited on single crystal Si and Ti deposited on amorphous Si layers sequentially without breaking the vacuum was investigated using backscattering spectrometry and glancing-angle x-ray diffraction. For Ti deposited on amorphous Si, TiSi2 was formed with a rate proportional to (time)^1/2 and an activation energy of 1.8±0.1 eV. For Ti deposited on single crystal Si, the reaction rate was slower and the silicide layer was nonuniform in thickness. We attribute the difference in behavior to the presences of interfacial impurities in the case where Ti was deposited on single crystal Si.

Improvement of crystalline quality of epitaxial Si layers by ion-implantation techniques

We demonstrate that the crystalline quality of Si layers grown on sapphire substrate (SOS) by the CVD method can be greatly improved through the use of implantation of Si ions and subsequent thermal annealing at relatively low temperatures (∼550 °C). This method utilizes an amorphous layer created by ion implantation near the sapphire/Si interface. Subsequent regrowth of this amorphous layer starting from the relatively perfect Si surface region leads to a much improved Si crystalline layer, as evidenced by MeV 4He+ channeling and TEM measurements. When the implantation‐formed amorphous layer is located at the outer portion of the Si layer, thermal annealing leads to only a small reduction in the amount of defects in the regrown layer as compared to the unimplanted sample. In these layers, epitaxial regrowth occurs with the same rate and activation energy observed in self‐ion‐implanted 〈100〉 Si.

Alloying Behavior of Au and Au–Ge on GaAs

Although Au–Ge has often been used in making Ohmic contacts to GaAs, the alloying behavior of this system has not been well characterized and understood. In this paper the behavior of Au and Au–Ge layers on GaAs was investigated as a function of processing temperature (400–600°C) and time by backscattering and channeling‐effect measurements with 2‐MeV 4He ions. Scanning electron microscopy and current‐voltage evaluations were also made. Similarities are found in both systems: There is a deeply penetrating component of Au into the GaAs that remains essentially unaltered once the surface Au has been consumed; a disordered region near the surface is found, the amount of which increased with increased process times. No significant amount of Au is found on substitutional or tetrahedral interstitial sites within about 3000 A of the surface. The presence of the Ge does have a significant effect: Complete alloying occurs at lower temperatures, and Ohmic contacts are formed. Scanning‐electron‐microcope displays in...

OUTDIFFUSION THROUGH SILICON OXIDE AND SILICON NITRIDE LAYERS ON GALLIUM ARSENIDE

Backscattering of MeV 4He ions has been used to analyze the Ga and As content in SiO2 and Si3N4 dielectric layers deposited on single‐crystal GaAs substrates. Changes in impurity concentrations and distributions are seen after isothermal annealing at both 750 and 800°C. Evidence for Ga outdiffusion is clear.

Analysis of amorphous layers on silicon by backscattering and channeling effect measurements

Abstract Backscattering and channeling of MeV 4He ions in single crystals covered with amorphous layers are discussed with the particular purpose of employing this nondestructive method to determine depth dependence of the composition, density and the total thickness of such layers. The analysis shows that the ratio of concentrations (and a relative depth scale) can be found directly from the experimental curves. To determine the absolute concentrations and depth scale independent measurement of stopping powers or layer thickness is required. Oxide layers grown on single crystal Si were used to verify the analytical results and, furthermore, we show illustrative analyses for samples with unknown characteristics. This technique may be applied rather extensively to the analysis of thin films.

Comparative study of surface roughness measured on polysilicon using spectroscopic ellipsometry and atomic force microscopy

Abstract Polysilicon layers prepared by low-pressure chemical vapor deposition at 560°C, 620°C, 660°C, and 700°C were measured by Atomic Force Microscopy (AFM) and Spectroscopic Ellipsometry (SE). Morphology, cross-sectional profile, roughness spectral density, and roughness of the surfaces were investigated by AFM using window sizes of 1×1 μm2, 10×10 μm2, and 50×50 μm2. The layer structure and the surface roughness were determined by SE using the Bruggemann-Effective Medium Approximation (B-EMA). The Root Mean Square (RMS) and mean square (Ra) roughness values measured by AFM were compared to the thickness of the top layer of the SE model describing the surface roughness. Although AFM results depend on the used window size, good correlation was found between the roughness values determined by AFM and SE for each window sizes. The results show that SE calibrated with AFM could be used for quantitative surface roughness determination.

Nondestructive determination of damage depth profiles in ion‐implanted semiconductors by multiple‐angle‐of‐incidence single‐wavelength ellipsometry using different optical models

Several‐parameter fitting of multiple‐angle‐of‐incidence ellipsometry data is developed to characterize near‐surface layers on semiconductors damaged by implantation. The damage depth profiles were described by either rectangular, trapezoid‐type, or coupled half‐Gaussian (realistic) optical models. The rectangular model has three parameters: the average damage level and effective thickness of the implanted layer, plus the thickness of the native oxide. The trapezoid‐type model is enhanced with a fourth parameter, the width of the back (a/c) interface. The realistic optical model consists of a stack of layers with fixed and equal thicknesses and damage levels determined by a depth profile function (presently the coupled half‐Gaussians). Five parameters were used: the center, the height, and two standard deviations of the profile, plus the thickness of the native oxide. The complex refractive index of each layer is calculated from the actual damage level by the Bruggeman effective medium approximation. The ...

Influence of Cu as an impurity in Al/Ti and Al/W thin‐film reactions

Thin‐film reactions of Al/Ti and Al/W with 3 at. % Cu in Al were investigated by glancing‐angle x‐ray diffraction and Rutherford backscattering for vacuum annealing in the temperature range 300–500 °C. In the Al/Ti system, the intermetallic phase Al3Ti grows as (time)1/2. The presence of Cu in Al retards the growth rate by an order of magnitude at 400 °C and increases the activation energy from 1.8±0.1 to 2.4±0.1 eV. In the Al/W system, the presence of Cu retards the penetration of W into Al.

Continuous carbon nanotube production in underwater AC electric arc

Abstract A simple, low cost and continuous growth method for the production of well graphitized multi-wall carbon nanotubes is described. The growth takes place in an AC arc in water between two carbon electrodes. At a voltage of 40 V the arc is stable in the range of 85–45 A, lower current values help in increasing the fraction of carbon nanotubes in the product.