G. Battistig

A very narrow resonance in 18O(p, α)15N near 150 keV: Application to isotopic tracing. II. High resolution depth profiling of 18O☆

Abstract Various depth profiling experiments illustrating the high depth resolutions obtained are presented for Ta 2 O 5 and SiO 2 layers with sharp 18 O 16 O interfaces in depth ranges up to some hundreds of angstrom. A further increase of depth resolution is reached by resorting to glancing geometry with respect to the beam. The depth sensitivity of this resonance is actually so high that it is the energy straggling induced by the ubiquitous hydrocarbon contamination layer on the sample surface that limits the near-surface resolution. The experimental curves are interpreted with the stochastic theory of energy loss. The results are compared to those obtained with the previously used resonances for 18 O depth profiling. Applications of these techniques to the isotopic tracer study of the microscopic growth mechanisms of SiO 2 on silicon are shown. Operated in UHV this method may yield potentially nanometric or even subnanometric near surface depth sensitivities, as illustrated by detailed theoretical calculations corresponding to ideal but realistic experimental conditions. These results illustrate the usefulness for very high resolution depth profiling of low energy narrow resonances in general due to the corresponding large d E /d x values.

A very narrow resonance in 18O(p, α)15N near 150 keV: Application to isotopic tracing: I. Resonance width measurement

Abstract The narrow resonance in the 18O(p, α)15N nuclear reaction reported by the Munster group at 152 keV looks very promising for high resolution depth profiling of 18O, being isolated and corresponding to large d E d x values. Its width was investigated usin the 2.5 MV Van de Graaff accelerator of GPS that has a proton beam energy spread of ≈ 80 eV FWHM at this energy. The α counting rate from this rather weak resonance was enhanced by operating an annular surface barrier detector subtending a large solid angle. The measurements were carried out on Ta2O5 targets prepared by anodizing polished high purity tantalum foils in 2% KCN aqueous solutions enriched to 98% 18O, using a vacuum line dedicated to the handling of H218O chemically purified with proper distillation techniques. The thicknesses of the various targets were controlled by the voltage applied to the special anodizing cell. Assuming a Breit-Wigner shape for this resonance, its width was deduced from a careful measurement of the practically background free low energy tails of thick target excitation curves. The use of the stochastic theory of energy loss for interpreting the results and the fit of the very short low energy tail found suggests that the most probable value of the width is Г = 50 eV . This unexpectedly narrow resonance appears to be an exceptionally efficient tool for very high depth resolution isotopic tracing of 18O, as will be shown in the second part of this paper.

Thermopile antennas for detection of millimeter waves

A thermopile structure is proposed for the detection of microwave/millimeter wave radiation. The thermopairs in the suggested linear arrangement function as antennas. 5.58 V/W responsivity was achieved at 100 GHz with 40 serial connected thermopairs. The experimentally observed polarity and frequency dependence convincingly verify the proper detector operation.

Enhancement of oxidation resistance in Cu and Cu(Al) thin layers

High conductivity and good resistance to electromigration makes copper a promising interconnect material in microelectronics. However, one of its disadvantages is the poor corrosion resistance. Two methods of passivation are investigated and compared: Al alloying and BF a ion implantation. X-ray diAraction (XRD) and Rutherford Backscattering Spectrometry (RBS) show the oxidation inhibition of both methods, but the diAerent ratio of CuO2 to CuO phases suggests diAerent mechanisms of passivation. There are no definite oxide lines in the XRD spectrum of the implanted and annealed Cu(Al) sample, so the presence of Al and the implantation together give increased protection against oxidation. The diAerence between the two mechanisms of oxidation inhibition is discussed briefly. ” 1999 Published by Elsevier Science B.V. All rights reserved.

Oxidation of SiC investigated by ellipsometry and Rutherford backscattering spectrometry

Oxidation of SiC was performed in Ar–O2 mixture of atmospheric pressure at 1100 °C and compared with that of Si. The partial pressure of O2 varied from 100 to 1000 mbar, while the oxidation time ranged from 0.5 to 45 h. The thickness of the oxide films was determined by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The time and the pressure dependence of the oxidation kinetics of SiC are well described by the modified Deal–Grove model. In the diffusion-limited region, even for the faster case, the oxidation kinetics of the C-terminated face of SiC is not clearly limited by oxygen indiffusion, as for pure silicon. To interpret the ellipsometry spectra, two models of possible structure were used. In the case of the one-layer model, for layer thicknesses above 30 nm, the refractive index of the oxide layers is identical to that of thermally oxidized Si, and it increases rapidly with decreasing thickness below about 15 nm. This increase is significantly larger for C-terminated than fo...

Morphological investigation of porous samples by resonant backscattering spectrometry

Abstract When performing backscattering spectroscopy measurements slightly above the energy where a sharp resonance exists in the elastic scattering cross section a characteristic resonance peak appears in the energy spectra of the backscattered particles. Unlike homogeneous samples where the position and width of this peak are mainly determined by the experimental set-up (incident energy, resonance width, etc.) for porous materials the peak width depends on the structure of the sample. This effect is caused by fluctuations in the stopping power along the trajectories of incident and scattered ions. Using the 3045 keV resonance in the 16 O(α,α) 16 O reaction for analysing oxidised porous silicon samples, it was demonstrated both experimentally and theoretically that: (i) the widening of the resonance peak is easily observable, (ii) it is closely related to the actual morphology of the samples and (iii) it can be applied to determine morphological details, as porosity, average pore diameter and anisotropy of the pore directions.

A characterisation of the morphology of porous silicon films by proton energy loss fluctuation measurements with a narrow resonance in the 15N(p,αγ)12C reaction

The morphology of highly porous silicon films of the “columnar” and “sponge-like” type was studied with transmission electron microscopy (TEM) and by decoration of the large internal surface of the films with 15N and by subsequently recording at various angles of incidence ψ the excitation curves of the 120 eV wide resonance of the 15N(p,αγ)12C reaction at 429 keV. The curves exhibit a flat plateau, demonstrating the uniformity of the decoration, and a trailing edge that decreases markedly slower than what usual energy straggling would induce. The corresponding excess of the energy loss fluctuations at the film-substrate interface are related to the morphology of the porous structure. However, a strong anisotropy of the trailing edge broadening is observed for the films of columnar type while for those of sponge-like type the broadening, smaller but still observable, is isotropic. Rocking curves recorded as a function of ψ at well chosen proton energies show for columnar type films that the average direction of the pore axes is identical, to within ±0.1°, with the (100) crystal axis of the substrate. The observed anisotropy for films of columnar type appeared to change notably with various thermal treatments to which they were subjected. This method yields hence a simple, fast and sensitive method of characterisation of the morphology of porous silicon films, complementary to TEM. The advantages of this method with respect to the use of Rutherford backscattering techniques are discussed in detail.

Damage accumulation in nitrogen implanted 6H-SiC: Dependence on the direction of ion incidence and on the ion fluence

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500keV N+ implantation at room temperature into 6H‐SiC is investigated. The irradiation was performed at different tilt angles between 0° and 4° with respect to the ⟨0001⟩ crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5×1014–3×1015cm−2. A special analytical method, 3.55MeV He+4 ion backscattering analysis in combination with channeling technique (BS∕C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS∕C spectra, the average electronic energy loss per analyzing He ion for the ⟨0001⟩ axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induced disorder profiles. Significantl...

Studies of boron-interstitial clusters in Si

The large number of self-interstitials created during implantation mediate the fast transient diffusion of implanted boron, leading to clustering. Sophisticated annealing strategies based on knowledge of the formation energy of the clusters are required to achieve full activation of the implant. In recent years attempts have been made to determine these data a priori from theoretical calculations. However, energy calculations alone are not sufficient to establish the key players in the clustering process of boron. The present paper describes a systematic first-principles quantum mechanical study of the characteristic vibration frequencies of a large number of boron–interstitial clusters (including possible configurational isomers). Comparison with the first Raman spectra obtained on B-implanted samples after high temperature annealing is presented.

A study of the initial stages of the oxidation of silicon using 18O2 and RTP

Abstract The growth mechanisms of the first steps of silicon oxidation at high temperature were studied. The rapid thermal oxidation under a static pressure (40 or 84 mbar) of oxygen isotopically labelled gas (18O2) has evidenced a linear rapid initial growth rate before the classical linear-parabolic Deal and Grove law prevails. The analyses of the 18O depth profile in oxide films formed by sequential oxidations, under dry 16O2 followed by 18O2, suggest an interpretation accounting for the rapid initial oxidation rate: the appearance during the first seconds of non-oxidized silicon fragments in the freshly formed silica network.