Electron-beam and sputter-deposited Ta silicides on GaAs were annealed in an As2 overpressure ambient to temperatures as high as 920°C for 20mim. The films were then characterized with RBS, cross-sectional TEM and both electron and x-ray diffraction. The morphology of sputtered TaSi2/GaAs interfaces did not change, however, some interaction was detected at electron-beam deposited GaAs/silicide interfaces. Arsenic in-diffusion was detected at temperatures above 800°C and it was found to be dependent on the stoichiometry of the films. Arsenic diffusion into Si-rich electron-beam and sputter deposited films was low, whereas significantly more As diffused into the Ta-rich silicide. Some indium (3×l015atoms/cm2), from the InAs used as the source of As2overpressure, was observed to accumulate at all GaAs/silicide interfaces at temperatures above 800°C.

The performance of TiN as a diffusion barrier in Au/TiN/InP structures has been studied and compared with Cr and Pt under identical conditions. In order to sensitively monitor interdiffusion, a novel SEM-EDX technique has been used to determine interdiffusion coefficients and activation energies in the temperature range 250–700°C. Extensive intermixing for Cr and Pt was indicated by the SEM-EDX technique and this was confirmed by Auger depth profiling. In addition the heterogeneous formation of the brittle intermetallic phase Au4 in was detected by XRD, and marked the catastrophic failure of the metallization due to delamination. These interfacial reactions and copious interdiffusion may be controlled by a TiN diffusion barrier which remains impervious for periods in excess of 24h at 500°C.

The effect of Cu on the kinetics of compound formation between Al and transition metals such as Hf and Ti has been studied by resistivity measurement and Rutherford backscattering (RBS) in the temperature range of 325°C to 450°C. Thin film couples consisting of 150nm-thick transition metal film and 600nm-thick Al-Cu film were used, in which the Cu content was varied from 0 to 9 wt%. The intermetallic phases were found to grow as (time)1/2. Most interestingly, the reaction rate constants were found to decrease significantly with increasing Cu content, but to level off for Cu contents greater than about 2 wt%. The corresponding activation energy for a given Altransition metal reaction was found to increase with increasing Cu for Cu contents up to 2wt%. For example, when 4 wt% Cu is added to Al, the rate constant at 400°C for HfA13 is reduced by about a factor of 5, while the activation energy increases from 1.5 eV to 2.0 eV. RBS results indicate that the Cu addition seems to inhibit the diffusion of Hf into Al. Diffusive intermixing in the Al/Ti system is much smaller and, consequently, the effect of Cu additions in preventing Ti diffusion into the Al is also much smaller.

X-ray diffraction (XRD) and Rutherford backscattering analysis (RBS) have been used independently to study the interface reaction of copperaluminum thin film couples during in-situ annealing in the temperature range 157°–220°C. For the X-ray studies a high vacuum annealing system was constructed on a Huber-Guinier thin film goniometer base1. This system enabled us to monitor the thin film interface reaction via changes of integrated X-ray intensities during the annealing treatment. RBS analysis was carried out with an existing in-situ heating stage. Using both techniques isothermal annealing experiments were carried out for four different temperatures. For this study 900Å Cu/1600Å Al and 1800Å Cu/3200Å Al thin film couples were prepared by sequential evaporation onto water cooled oxidized <111> silicon and MgO substrates.

Implantation range parameters and diffusion characteristics of As, B, and P in TaSi2 have been investigated, mainly by SIMS. It is shown that dopant diffusion in the silicide is much faster than in polycrystalline Si. Significant outdiffusion is observed for P, segregation effects are seen with B only. No dopant penetration through gate oxide is detected.

We have shown that the irradiation of a wide variety of thin film-substrate combinations with MeV/amu ions leads to greatly enhanced adhesion. The systems studied include metal films on dielectric, semiconductor, and metal substrates. For metal coatings on semiconductors the electrical contact which is originally diode-like becomes ohmic. Metal films on metal or polymeric substrates generally require the lowest dose irradiations. For Au on Ta the threshold dose to achieve a constant level of adhesion (“Scotch Tape” test) is consistent with a model of the process in which the dose threshold varies with the electronic excitation part of the energy loss in the material as (dE/dx + Q)−2 . The value of Q obtained corresponds to an exothermic reaction due to the increased binding that liberates ˜70 eV at the interface. This model and a variant of it based on the production of K-shell vacancies in low Z elements in the target will be discussed.

Ion beam enhanced adhesion has been studied for the case of thin Cu films deposited on substrates of alumina, fused quartz and glass-ceramic. Beams of He+ (200 keV) and Ne+ (280 keV) were used, in order to test the respective roles of nuclear and electronic interactions in this process. Peel tests were used to produce the first quantitative studies of adhesion strength as a continuous function of ion dose. Bond strengths improved after irradiation at modest doses, sometimes by a factor of 20. Subsequent heating in a helium furnace produced as much as an order of magnitude further adhesion improvement in irradiated samples. Similar tests for Cu on Teflon produced excellent bonding for ion doses of ∼ 1014/cm2. The results indicate bond breaking and reconstruction at a sharp interface, with no significant metalsubstrate intermixing. The new bond is stable under heat cycling.

Helium ions of 2 MeV energy and electrons of 5 to 30 keV energy have been used to irradiate a variety of thin (10–330 nm) metal films after deposition on semiconductor and insulator substrates. Dose thresholds for increased adhesion were found following irradiation with either type of particle. It is argued that the stronger bonding arises from an electronic, rather than a collisional, process. Representative results are presented and discussed within the framework of a recent model for heavy ion-induced effects.

The effect of γ-ray and electron irradiation on the adhesion of gold films to PTFE has been ascertained. The film adhesion has been found to undergo a sharp increase at a γ-ray dose of 5 × 106 to 1 × 107 rads. Qualitative ‘Scotch tape’ tests also show an increase in adhesion when the films are irradiated with electrons (250 eV - 3 keV).

Examination of the interface region of very thin (∼ 20 Å) gold films on PTFE by X-ray photo-electron spectroscopy indicates the increase in adhesion results from radiolytic processes and consequent chemical interaction with the gold.

The influence of electron and ion irradiation on the adhesion at chromium-copper thin film interfaces has been studied. The measurements were carried out with different types and thicknesses of well-characterized oxides at the interfaces. The electron energies were varied between 5 and 10 keV, with doses up to 10 18cm −2. lons of He +Ne+and P+ were used in the range of energies between 150 keVand 1.0 MeV, with fluences ranging from 1015 cm−2 to 6× 10 16cm−2 . Substantial improvement of the adhesion is observed in cases where the beam has a significant nuclear stopping power component. Electronic processes may also play a role in improving adhesion, although they are not dominant in the case of the present films.

Recent results on the effects of high energy ion beam irradiation in polymer films are reviewed in this paper. High energy ions (>10 keV/amu) deposit a large amount of energy (∼several cV/atom) in ionizing the electrons of the target atoms. This results in significant destruction of bonds in the films as a result of which polymers undergo rapid dissociation. Using a quadrupole mass spectrometer the study of transient emission of molecular species produced by an ion pulse has been shown to yield information about the diffusion and reaction kinetics of various molecules in the polymer. The fact that polymers undergo dissociation and those atoms which form volatile species are selectively depleted from the film could be utilized in producing useful inorganic composites by ion bombardment of polymers. For example, hard SiC composite films have been produced by ion beam irradiation of organo-silicon polymers. Eventually, polymer dissociation leads to a predominately carbon containing film which exhibits interesting electronic transport properties. Experiments on ion irradiated, pure carbon films indicate that a metallic form of carbon is produced from the polymer films at high irradiation doses.

Electronic excitation in thin polymer films by MeV ion beams and on-line transient mass spectroscopy together provide a new opportunity for measuring the diffusion of molecules in polymers even when the diffusion coefficients are <∼ 10−10 cm2 s−1.With a quadrupole mass spectrometer, we have obtained transients of several molecular species from a variety of polymers bombarded by 2 MeV helium and argon ions.We have measured, for example, transient emission of D2, CO, CO 2, CD3OD, etc., from deuterated Poly(methyl methacrylate), PMMA.The beam fluences required for the measurements are sufficiently small that they cause minor perturbation in the structure of the film. The exciting ion pulse is typically 15 seconds wide with fast (<msec) rise and fall times. However, the emission signal of m−46 (COOD), for example, shows a slow build-up with a gradual fall after the beam is turned off with a tail lasting several seconds. The experimental data for the above molecule has been fitted to a one-dimensional diffusion model and the diffusion coefficient deduced from three different film thicknesses is ∼8−±2×10−11 cm2S−1 Since very thin films can be used in these experiments, still smaller D values are measurable. The sample requirements are simple and even the presence of pinholes will not affect the measurements significantly. Techniques that completely avoid any possible effects of ion damage tracks and an example where chemical reaction is the rate limiting step will be discussed.

Ion beam modifications to thin film, polycrystalline Ni-Al alloys have been investigated using high resolution (0.1 eV FWHM) transmission electron energy loss spectroscopy (EELS). The ion induced modification of Ni3 AI,NiAI, Ni2Al3, and NiAl3 as measured by EELS, are compared to concurrent electron microscope diffraction analyses. The EELS coresub level spectra corroborate the NiAI3 to amorphous phase transition observed by diffraction, while the EELS valence spectra provide a signature for the Ni2Al3 to NiAl phase transformation. These results reflect the changes in the electronic states caused by changes in the crystal structure. In addition, perturbations to the electronic states are measured even when no change appears in the diffraction pattern (irradiated NiAl). Thus, high resolution EELS is shown to be a sensitive analytical technique for studying ion irradiated materials.

Variations in the valence and core level electron energy loss spectroscopy (EELS) peaks are studied as a function of nickel silicide composition.Analysis of the EELS spectra in comparison with the electron diffraction patterns show the plasmon energies fingerprint the silicide phases. The EELS core level spectra reflect the Si bonding and the electronic density of states in each phase.Irradiated Ni 2Si becomes amorphous causing a change in the plasmon peak energy and the Si L23peaks.

The ion beam induced reactions at Fe-Si interface are studied for the first time using a novel interface-sensitive Mössbauer probe.The samples used in these studies are prepared by depositing a thin layer (<450A°) of enriched Fe57 isotope (95.45% by composition) on a freshly cleaned silicon (111) substrate followed by a deposition of a 150Ao film of natural iron (Fe 57 only 2.2%).These samples are subjected to Xetion bombardment at an incident ion energy of 100 keV and a dose of 6 × 1015 ions/cm2 The technique of Conversion Electron Mössbauer Spectroscopy (CEMS) is used to characterize the formation and growth of different phases as a function of annealing treatment. The spectra are leastsquare fitted using the MOSFIT programme.The MHssbauer lines for as-deposited and ion bombarded samples show a considerable broadening, which is a clear signature of a large concentration of defects formed at the interface due to ion beam induced collision cascades. As the samples are annealed the resonance lines are sharpened indicating recovery of stoichiometrically well-defined phases from an initial defective state. The present study indicates formation of FeSi and Fe3 Si phases after the annealing treatment-RBS measurements are used to confirm the mixing.These results are analyzed in terms of the non-equilibrium features of the directed energy processing of interface.

The physical processes associated with the formation of various normal as well as metastable phases at an ion beam mixed Fe-Al interface are studied by using a novel interfacesensitive Conversion Electron Mbssbauer Spectroscopic (CEMS) technique.This technique which has been introduced and used for the first time in these investigations, is based on the deposition of a thin (less than 50 A°) layer of enriched Fe 5 7 isotope (95.45% by composition) at the interface between the aluminium substrate and a post-deposited 250A° film of natural iron (only 2.2% of Fe 57), leading to a considerably enhanced spatial selectivity of the M~ssbauer information regarding the reactions occurring at the interface.A number of samples prepared in the manner mentioned above are subjected to an argon ion bombardment at an incident ion energy of 100 keV and a dose of ≃ 2 × 1016 ions/cm2 The ion beam mixed samples are annealed at different temperatures in the range between 300°C to 600°C for twenty minutes, to provide the thermal energy for the growth of different Fex Aly phases at the interface.Conversion Electron Mössbauer Spectroscopy is employed at each stage of the ion beam processing and annealing of the samples, to characterize the phases formed. All the Mbssbauer spectra are least square fitted using the MOSFIT programme to obtain the best-fit values of Mössbauer parameters. The results indicate a substantial broadening of the Mössbauer lines for the as-implanted samples, a fact which can be attributed to the beam induced radiation damage. Subsequent annealing of the samples at different temperatures leads to annealing of damage and further to the formation of Fe3 Al and FeAl solid solution. Mössbauer spectra of the samples annealed at 500°C indicate segregation of Fe at the interface along with the formation of Fe3Al phase, while annealing at 600°C results in the formation of Fe-Al solid solution phase with traces of effectively unreacted metallic Fe. The unimplanted composites heat-treated in an identical manner do not show these features. These results which are supported by RBS measurements, are interpreted and discussed in terms of the non-equilibrium nature of the ion beam processing of the interface.

Rutherford backscattering and channeling techniques, transmission electron microscopy and Auger electron spectroscopy have been combined to investigate the reordering of implanted amorphous Si in the presence of an Al surface layer and the interdiffusion between these two elements. Recrystallization took place at 200°C and proceeded as the temperature increased. At 350–400°C, better epitaxial layers were obtained and channeling effects became observable. Substantial concentration of residual damage was observed in the regrown layer and persisted to high annealing temperatures. The concentration of Si in the Al film was far beyond the solid solubility at annealing temperatures. When ion implantation was performed at 200°C, the implanted layer was virtually defect free and the diffusion of Si into Al was suppressed.

Attention is focused on the interactions which occur when lattice dislocations impinge on interfaces (i.e., grain boundaries, crystal/crystal interphase boundaries and crystal/amorphous boundaries) in solids. The lattice dislocations can generally dissociate into interface dislocations possessing smaller Burgers vectors under a driving force produced by a decrease in the elastic energy. For crystal/crystal interfaces, a wide range of possibilities exists, depending upon the grain boundary type, which extends from dissociation into a discrete number of interface dislocations to dissociations into a distribution consisting of, in the limit, an infinite number of interface dislocations possessing infinitesimal Bur.ers vectors. For crystal/ anorphous interfaces, the latter model is applicable. Examples of dissociations in these various interfaces are presented. The dissociation geometries and kinetics are described briefly. Some of the wider implications of these phenomena are mentioned.

Observations of antiphase disorder obtained using a new technique of transmission electron microscopy, in (100) epitaxial layers of GaAs:Ge produced by MBE are presented. The crystallographic origin of this type of disorder is analysed using a recently developed approach. It is shown that antiphase disorder can exist in epitaxial layers where the substrate orientation is of the form {hko}this is consistent with experimental observations that disorder is observed on (100) and (110) substrates, but not on (111) or (211), for example. Antiphase boundaries in {hko} specimens are shown to separate interfacial domains which are energetically degenerate and related by symmetry operations.

The energies of the Σ = 5, 13, and 17 (001) coincidentsite lattice (CSL) twist boundaries in Al containing small amounts of Zn solutes have been calculated using an iterative energy minimization technique in conjunction with interatomic potentials derived entirely from first principles. By determining both the energies of substitution in the bulk and in different sites in the boundary, the site selectivity for Zn segregation at the grain boundary has been investigated. In the lattice plane immediately near the grain boundary, Zn solutes were found to prefer the lower-symmetry non-coincidence sites while, in the next plane, substitution in the coincidence sites is preferred. The effect of Zn-Zn interactions has also been considered for small solute concentrations. It is found that the magnitude of the Zn-Zn interaction energy is remarkably insensitive to the particular sites occupied by the Zn atoms as well as the detailed geometry of the interface.