Al2O3/Al/Al2O3 microlaminates of nominal thickness 750 nm were formed by physical vapor deposition (PVD) and ion beam assisted deposition (IBAD). IBAD influences the residual stress in the layers, their strength and mixing of the metal-ceramic interface. Different combinations of PVD- and IBAD-synthesized layers were used in trilayer microlaminates which were then tested in tension for cracking behavior. Residual stress states of the microlaminates are reproducible and follow a rule-of-mixtures of the constituents. IBAD of monolithic oxide causes an increased residual compressive stress and results in a slightly larger strain to fracture over the PVD oxide. Trilayer microlaminates exhibit lower saturation crack densities compared to monolithic oxides due primarily to the introduction of a ductile layer. The variation in strength of the ductile layer (by IBAD) and mixing of the interfaces do not appear to affect the fracture behavior, which is understandable in a strong bond-forming system. Observations are consistent with a cracking mechanism that is controlled by the flaw distribution in the brittle oxide layer.
New aspects of surface treatment by gas cluster ion beams are discussed. Molecular dynamics simulation has shown that a considerably high damage region is formed at a depth exceeding the mean projected range of the implanted atoms. High yield sputtering has also been shown to occur with respect to lateral sputtering. Experiments on shallow implantation, high yield sputtering, surface smoothing and low damage surface cleaning were performed. The obtained results are compared with those of conventional monomer ion irradiation. Possible applications of ionized cluster beams to a new area of surface modifications are discussed.
Analysis of random and channeled He stopping powers and of random and channeled B ranges in Si suggest that the non-local fraction xnl of the electronic stopping is energy dependent. It is proposed that xnl can be written as a power of the random stopping power Se. For low energies, where the random stopping power may be described by a power law, this model reduces to the model previously proposed by Hobler. The model is in good agreement with published B ranges and with the range of new [110] B channeling implantations at 2–3 MeV. Moreover, it is found that employing the ZBL stopping power overestimates the random range of B implantations in Si between about 100 keV and 1 MeV. It is shown that the exponent in the power law at low energies for the random stopping power Se is 0.5 rather than 0.375 as proposed by ZBL.
〈100〉 and 〈111〉-Ge single crystals were preamorphized in a thin surface layer using 50 keV or 85 keV N+ ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) at the amorphous/crystalline interface were studied using different kinds of high energy ion beams. The crystallization rate for the 〈100〉-Ge is about 1.5 times higher than that for 〈111〉-Ge. The total recrystallised thickness depends mainly on the nuclear energy deposition and the irradiation temperature. Interfacial amorphization is detected in Ge for the first time. Cross section TEM micrographs show a sharp amorphous/crystalline interface for both IBIEC and IBIIA. The fit of the experimental data yields an activation energy of 0.82 eV for IBIEC and 1.16 eV for IBIIA.
A detailed study of the activation kinetics of silicon implanted GaAs has been carried out for implantation energies ranging from 100 keV to 2 MeV, with ion fluences chosen to give silicon concentrations in the useful range of between 1017 and 1019 Si cm−3 for all the implant energies studied. Anneal times have been varied over three orders of magnitude to give information relating to both RTA and furnace anneals with the temperatures being varied from 700 to 1150°C. The effect of compositional changes in the dielectric encapsulant has also been studied and shown to be a major variable in the activation mechanism. SIMS analysis has been compared with TRIM simulations to give information on the atomic concentration of the implanted silicon. Following annealing, differential Hall effect measurements have been used to obtain electron concentration and mobility profiles for comparison with the atomic concentration and implant induced disorder profiles. In this paper, the role of implantation damage, vacancy distribution and implant dopant concentration is discussed in conjunction with a model for the activation of silicon implants in GaAs.
The charging and etching effects of hydride and fluoride gases in plasma immersion ion implantation (PIII) doping experiments have been investigated. Both phenomena can affect implant profile and dose, alter device structure, and degrade device reliability. In addition, charge accumulation significantly reduces implant energy. Helium is a good choice as a diluting gas for PIII doping processes due to its low ionization rate, inertness, and minimal etching and charging effects.
Ion beam techniques are frequently used to modify the physical properties of materials. It is the aim of this contribution to obtain information on ion beam effects on irradiated metal/ceramic interfaces with bilayer geometry. Ion beam mixing and radiation enhanced diffusion have been investigated in CuAl2O3, AuAl2O3 and AuZrO2 samples. Specimen, with thicknesses of the metallic film in the range of 60–70 nm, were prepared by vapor deposition and irradiated with 150 keV Ar+ ions in the range of 0.9 × 1016 to 1.5 × 1017 Ar+/cm2. Sample temperature during irradiation was varied between 77 K and 673 K. The mixing behaviour was analysed using concentration depth profiles measured by Rutherford Backscattering Spectroscopy (RBS). The results show that mixing efficiencies for all elements scale linear by the Ar+ ion dose. Radiation enhanced diffusion is separated from temperature independent mixing processes. High resolution scanning electron microscopy (HREM) showed strong surface deterioration for the AuAl2O3 and AuZrO2 samples. X-Ray Photoelectron Spectroscopy (XPS) analysis in the particular case of the CuAl2O3 interface was performed.
This contribution focuses on the techniques, ion beam synthesis, molecular beam allotaxy and wafer bonding, which allow the fabrication of buried, dielectric and metallic or semiconducting silicide layers in single crystalline silicon. Many of those heterostructures cannot be grown by standard deposition techniques, because of incompatible crystal structures or inappropriate lattice mismatch. The principles of the various techniques, their basic mechanisms and their potentials are discussed. Most emphasis is placed on buried epitaxial CoSi2 in Si(100), because of the excellent compatibility of this compound with silicon and silicon technology. It will be shown that such single crystalline “silicon on metal” structures are useful substrates for numerous applications.
Glassy Polymeric Carbon (GPC) samples prepared from a precursor possess accessible pore volume that depends on the heat treatment temperature [G.M. Jenkins and K. Kawamura, Polymeric Carbons - Carbon Fiber, Glass and Char (Cambridge University Press, Cambridge, 1976) p. 140]. We have shown that lithium percolates without diffusion into the accessible pores of GPC samples immersed in a molten lithium salt bath at 700°C [D. Ila, G.M. Jenkins, L.R. Holland, A.L. Evelyn and H. Jena, Vacuum 45 (1994) 451]. Ion bombardment with 10 MeV Au atoms increases the total pore volume available for lithium occupation even for samples normally impermeable to lithium. The lithium concentration depth profile is measured using Li7(p,2α) nuclear reaction analysis. We will report on lithium percolation into GPC prepared at temperatures between 500°C and 1000°C and activated by a 10 MeV gold ion bombardment.
This paper reviews recent work using deep level transient spectroscopy (DLTS) for studying point defects in crystalline silicon implanted with H, B, C, O, Si, Ge and Sn ions. Doses between 107 and 1010 cm−2 and energies from 0.4 to 8 MeV were used. Different intrinsic and impurity-related defects like divacancy and vacancy-oxygen centers are identified and their formation has been studied as a function of dose, dose rate, sample depth, implantation temperature and ion mass. Recombination between vacancies and Si self-interstitials is found to play a major role and only a few percent of the generated vacancies form stable defects. Furthermore, in direct contrast to that for damage accumulation at doses above ∼ 1012 cm−2, the production of vacancy-type defects increases with increasing implantation temperature and decreases with increasing dose rate. These effects are qualitatively simulated using a simple model for the defect generation kinetics and attributed to enhanced vacancy annihilation by overlapping Si self-interstitials from adjacent ion tracks.
Electron cyclotron resonance (ECR) O2 plasmas, in conjunction with electron-beam evaporation of Al, were used to grow thick AlOx films with varying but controlled composition and microstructure. The ion energy was varied from 30 to 190 eV, and growth temperatures varied from 35°C to 400°C. The ECR-film compositions were varied from AlO0.1 to Al2O3 by controlling the plasma parameters and Al deposition rate. The Al-rich alloys exhibited a fine-grain (10–100 nm) fcc Al microstructure with γ-Al2O3 precipitates (∼ 1 nm), similar to those reported previously in gigapascal-strength O-implanted Al. The measured hardness of the ECR AlO alloys (∼ 3 GPa) was also comparable to that of the ion-implanted alloys which implies that the yield strength of the ECR material is ∼ 1 GPa. Moreover, the AlO alloys retain much of the elasticity of the Al metal matrix.
It is well established that ion irradiation of glassy carbon with energetic ions leads to the formation of a dense amorphous surface layer. In this work we show using cross-sectional TEM that oriented graphite-like regions are formed within the implanted layer of glassy carbon implanted with 50 keV C ions at high doses. The preferred orientation is such that the sp2 bonded graphite-like sheets lie normal to the implanted surface. Stress measurements of the implanted material show the presence of a biaxial compressive stress. Molecular dynamics simulations of a two-dimensional analogue of graphite show a similar preferred orientation effect. Thermodynamic calculations predict that a non-hydrostatic stress can result in preferred orientation in anisotropic materials such as graphite. The preferred orientation can be explained in terms of the combined effects of the mobility introduced by the implanted ions and the anisotropic stress field.
Non-stoichiometric single crystal spinel samples with composition MgO · 3Al2O3 were irradiated near (001) orientation with 400 keV Xe++ ions at 100 K to a dose of 1 × 1016 Xe/cm2, representing a peak damage level of 25 displacements per atom (dpa). Damage accumulation in the irradiated surface was assessed by cross-sectional transmission electron microscopy. A continuous crystalline layer was observed in the implanted region. The layer is oriented with the underlying substrate, but is highly defected and possesses a symmetry different than that of the bulk. This change in symmetry is revealed by the absence of diffracted intensity at first-order spinel reciprocal lattice positions. These results are compared with earlier observations on equimolar (001) MgO · Al2O3 single crystals irradiated with 400 keV Xe++ ions to the same dose and at the same temperature [N. Yu, K.E. Sickafus and M. Nastasi, Phil. Mag. Lett. 70(4) (1994) 235 (Ref. [1])].
This paper addresses the diffusion and gettering of Au to defects introduced by H-implantation in Si. Cz Si wafers of (100) orientation were first implanted with 50 keV and/or 100 keV H, and the damaged layers were then annealed at 850°C to drive the hydrogen out and leave a band of well-facetted cavities close to the original projected range. A known amount of Au was introduced by ion implantation in the near surface region. The profiles of Au were using Rutherford backscattering and channeling and the microstructure using cross-sectional transmission electron microscopy. The gettering of Au to cavities and the movement of Au from one cavity to another were studied as a function of time and temperature. The Au concentration at cavities is found to be strongly dependent on annealing time and the movement of Au from one set of cavities to another is found to be influenced strongly by the interplay between Au diffusion, solubility and the availability of strongly reactive bonding sites at cavity walls.
The residual damage in Si has been studied after ion implantation and annealing at elevated temperatures. The residual electrical and structural damage has been measured with capacitance-voltage, deep level transient spectroscopy and transmission electron microscopy. A correlation between the observable structural damage and the electrically active defects was observed. A critical dose is determined, below which no structural and electrically active defects are found. This dose is characterised for different implantation temperatures and implantation energies and therefore as a function of the initial damage present after implantation. Also discussed is the critical dose as a function of annealing parameters. The observed electrical compensation of the background concentration is found to be a result of neutral donor complexes and deep acceptors.
Ion induced desorption cross sections for Cu thin films (≤ 1 ML) on Ru(0001) have been measured by bombardment with Ne+ ions. The accurate calibration of the Cu coverage was carried out by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and low energy ion scattering (LEIS). Decreases in surface Cu as a function of ion dose were monitored for various Cu coverages by LEIS measurement. At 1 ML of Cu coverage, the desorption cross section was measured to be σD ∼ 2.03 × 10−15 ions/cm2, or a sputtering yield of Y ∼ 3.2 at 1 keV. Application of binary collision sputtering models indicates that for E0 > 400 eV the Cu atoms are mainly removed by sputtered Ru atoms moving outward through the surface region.
We have employed low energy (5–100 eV) beams of C+, O+, and CO+ ions to deposit carbide and oxide layers on a Si(1 1 1) surface under ultrahigh vacuum (UHV) conditions at room temperature. The deposited layers are characterized in situ by Auger electron spectroscopy (AES) and ultraviolet photoelectron spectroscopy (UPS). The effects of sputtering and thermal treatment on these layers are also examined. Atomic C+ and O+ ion beams efficiently produce carbide and oxide layers, respectively. Molecular CO+ ions collisionally dissociate on the surface to form a mixed carbide and oxide phase, the dissociation yield for CO+ increasing with beam energy in the range of 5–20 eV. The electronic energy gained during ion neutralization plays an extra role for CO+ dissociation. Upon thermal annealing, the O+-deposited layer changes into a more uniform phase. The CO+-deposited layer exhibits higher thermal stability when produced from a higher energy beam, which can be attributed to deeper penetration of carbon and oxygen and their different depth distributions.
Damage and strain in high-dose O-implanted Si have been systematically studied with Rutherford backscattering spectrometry, double crystal X-ray diffraction and transmission electron microscopy. In the Si overlayer, tensile strain (lattice contraction) results from a vacancy excess. The depth of the strain maximum is a function of the O ion dose. For example, at low doses and an implant temperature of 150°C, the strain increases from the surface to the amorphous/crystalline interface, while at high doses, relaxation through dislocation formation is observed when the strain exceeds ∼6400 ppm and thereafter the residual strain maximum moves toward the surface. The strain maximum before relaxation at a given O dose decreases as the implant temperature increases. This is due to dynamic annealing effects and is consistent with thermally-activated dislocation nucleation and movement.
The near surface structure of low energy (0.5-1.5 keV) argon bombarded Si(100) was characterized using medium energy ion scattering and high resolution X-ray photoemission spectroscopy. The ion induced lattice damage, distribution and redistribution of incorporated argon and silicon carbide formed during the dynamic mixing process are directly and non-destructively measured and depth-profiled in the sub-nanometre scale. The results capture many details of low energy ion interaction with Si in the near surface and address the capability for direct and non-destructive characterization of such interactions in the sub-nanometre scale.
Buried CoxFe1−x and NixFe1−x silicides were prepared by consecutive metal implantation in Si(111). Transmission-electron microscopy analysis shows strong evidence for the formation of metastable ternary Co0.5Fe0.5Si2 and Ni0.5Fe0.5Si2 precipitates during implantation, the lattice structure of which is believed to be mainly B-type oriented (twinned) CaF2. Annealing of the samples at 1000°C results in coalescence of the silicide into continuous layers with sharp interfaces. During this high-temperature treatment, nearly full phase separation occurs in the case of Co0.5Fe0.5Si2, whereas for Ni0.5Fe0.5Si2 only the onset of phase separation is observed. Channeling spectrometry indicates a good alignment of the silicides with the substrate. Furthermore, all samples were studied with X-ray diffraction and Mössbauer spectrometry, in order to obtain detailed information on the strain and the phases present.
