Real-time Rutherford Backscattering Spectrometry Research Articles

Interfacial reaction and phase formation in Pd/ZrO/Pd/TiO/Pd multilayer stack on silicon substrate: Investigated by ion beam techniques

The influence of the annealing temperature on the stability of the multilayer stack Pd/Zr/Pd/Ti/Pd thin films system, with both Zirconium (Zr) and Titanium (Ti) layers containing oxygen (O), deposited on silicon substrate was investigated. Using the in-situ real-time Rutherford backscattering spectrometry (RBS) analysis, the multilayer stacked thin film systems were linearly heated, at a constant heating rate, from room temperature up to 600 °C and found to be stable up to ∼370 °C whereby the inter-diffusion of Palladium (Pd), from both the third and the fifth layer, towards the forth layer comprising of Ti and O in 2:1 ratio, was observed. Moreover, the Ti, from the Ti–O layer, was found to spread to low and higher channels during Pd diffusion. Above 480 °C the second reaction was observed between Pd and silicon substrate, forming a hexagon silicide phase (Pd2Si) confirmed by X-ray diffraction. The thickness of the Pd2Si layer increased with increasing temperature and its activation energy was estimated to be 2.30 eV, which is about 1.10 eV and 0.65 eV higher than the activation energy of the Pd2Si phase formation at 100 °C and 250 °C, respectively. Therefore, the activation energy of the Pd2Si phase depends on the temperature at which the phase is growing.

Spectrometry studies of Ag implanted silicon carbide thin films for application as a diffusion barrier against transition metals

A diffusion kinetics study of implanted silver (Ag) ions into SiC films is conducted. SiC thin films have been processed on Si (1 0 0) substrates by electron beam deposition from a commercial high purity hot-pressed SiC sheet. The as-deposited films were thereafter implanted with Ag+ ions. Realtime Rutherford backscattering spectrometry experiments showed that Ag+ is stable until 600 °C, which is the highest temperature that the heater in the system used could achieve. Conventional RBS studies on isochronally annealed films at higher temperatures in the range between 650 °C and 950 °C reveal that there is no significant change in the spectra up to a temperature of ∼ 750 °C. At 850 °C a change in the Ag implantation profile was observed, suggesting that Ag is mobile at that temperature. The corresponding depth profile at 850 °C suggests that there is significant Ag in- diffusion, however the overall integrated intensity data indicate that most of the Ag+ is escaping out of the films. Upon annealing for one hour at 950 °C, all the Ag ions have essentially escaped out of the films and/or spread throughout the layer below the detection limit of RBS. Isothermal annealing studies over varied duration times at 850 °C confirm Ag in-diffusion, but at the same time there is evidence of depletion of Ag near-surface regions as the annealing time increases; the overall out-diffusion of the implanted metal, although steady, is found to be slow in an isothermal process. FTIR investigations point to a diffusion model through pores and grain boundaries.

Effect of the annealing atmosphere on the layer interdiffusion in Pd/Ti/Pd multilayer stacks deposited on pure Ti and Ti-alloy substrates

Pd(50 nm)/Ti(25 nm)/Pd(50 nm) multilayer stack has been deposited on Ti and Ti6Al4V substrates; we have studied the intermixing of layers upon annealing at the hydrogenation temperature of 550 °C, under vacuum, H/Ar gas mixture and pure hydrogen atmospheres. Scanning electron microscopy (SEM) micrographs indicated surface roughening in samples annealed under vacuum and H/Ar gas mixture while those annealed under pure H2 remained relatively smoother. Rutherford backscattering spectrometry (RBS) revealed intermixing of layers as evidenced by the diffusion of Pd toward the bulk, while XRD indicated the formation of PdTi2 phase in the samples annealed under vacuum and H/Ar gas mixture atmosphere. In-situ, real-time RBS showed that the annealing under pure H2 preserves the integrity of the Pd catalyst. No indication of the PdTi2 formation in the pure H2 annealed samples was observed; instead only the TiH2 phase appeared, indicating the absorption of H into the system.

Growth and characterization of Pt-Si droplets for silicon nanowires synthesis

Abstract The formation of platinum silicide phases as a function of the annealing temperature was investigated using in-situ real-time Rutherford backscattering spectrometry. The in-situ real-time RBS revealed the reaction of platinum and silicon to start at about 220 °C to form platinum silicide phases, Pt2Si and PtSi in sequence. Scanning electron microscope revealed the morphological change in the platinum layer (formation of droplets) at 800 °C. The particle induced X-ray emission analysis showed the variation of platinum intensity, in the droplets areas, between 1600 and 2000 counts. The surrounding areas are left almost uncovered due to platinum film dewetting. In-plane as well as out-of-plane silicon nanowires were observed to form at 800 °C and 1000 °C using pulsed laser ablation and thermal annealing techniques, respectively.

In-situ RBS studies of strontium implanted glassy carbon

The diffusion behaviour of strontium in glassy carbon was investigated using in-situ real time Rutherford backscattering spectrometry. The sample was annealed in vacuum from room temperature to 650 °C. Diffusion of the implanted strontium towards the bulk was observed after annealing at temperatures ranging from 450 °C–560 °C. The diffusion depth was limited to the end-of-ion-range region where there was still some radiation damage present. No diffusion into the pristine glassy carbon was observed suggesting that diffusion of Sr in glassy carbon can only occur in regions with radiation damage. Annealing the sample at temperatures higher than 560 °C resulted in migration of the implanted strontium towards the surface of the glassy carbon substrate. The amount of the accumulated strontium at the surface increased as the annealing temperature is increased. The RBS spectra obtained after annealing the sample isothermally at 650 °C for 2 h show that there was no further diffusion and accumulation of the strontium during this period.

Interface reactions between Pd thin films and SiC by thermal annealing and SHI irradiation

The solid-state reactions between Pd thin films and 6H-SiC substrates induced by thermal annealing, room temperature swift heavy ion (SHI) irradiation and high temperature SHI irradiation have been investigated by in situ and real-time Rutherford backscattering spectrometry (RBS) and Grazing incidence X-ray diffraction (GIXRD). At room temperature, no silicides were detected to have formed in the Pd/SiC samples. Two reaction growth zones were observed in the samples annealed in situ and analysed by real time RBS. The initial reaction growth region led to formation of Pd3Si or (Pd2Si+Pd4Si) as the initial phase(s) to form at a temperature of about 450°C. Thereafter, the reaction zone did not change until a temperature of 640°C was attained where Pd2Si was observed to form in the reaction zone. Kinetic analysis of the initial reaction indicates very fast reaction rates of about 1.55×1015atcm−2/s and the Pd silicide formed grew linear with time. SHI irradiation of the Pd/SiC samples was performed by 167MeV Xe26+ ions at room temperature at high fluences of 1.07×1014 and 4×1014ions/cm2 and at 400°C at lower fluences of 5×1013ions/cm2. The Pd/SiC interface was analysed by RBS and no SHI induced diffusion was observed for room temperature irradiations. The sample irradiated at 400°C, SHI induced diffusion was observed to occur accompanied with the formation of Pd4Si, Pd9Si2 and Pd5Si phases which were identified by GIXRD analysis.

Effect of high temperature deposition on CoSi2 phase formation

This paper discusses the nucleation behaviour of the CoSi to CoSi2 transformation from cobalt silicide thin films grown by deposition at elevated substrate temperatures ranging from 375 °C to 600 °C. A combination of channelling, real-time Rutherford backscattering spectrometry, real-time x-ray diffraction, and transmission electron microscopy was used to investigate the effect of the deposition temperature on the subsequent formation temperature of CoSi2, its growth behaviour, and the epitaxial quality of the CoSi2 thus formed. The temperature at which deposition took place was observed to exert a significant and systematic influence on both the formation temperature of CoSi2 and its growth mechanism. CoSi films grown at the lowest temperatures were found to increase the CoSi2 nucleation temperature above that of CoSi2 grown by conventional solid phase reaction, whereas the higher deposition temperatures reduced the nucleation temperature significantly. In addition, a systematic change in growth mechanism of the subsequent CoSi2 growth occurs as a function of deposition temperature. First, the CoSi2 growth rate from films grown at the lower reactive deposition temperatures is substantially lower than that grown at higher reactive deposition temperatures, even though the onset of growth occurs at a higher temperature, Second, for deposition temperatures below 450 °C, the growth appears columnar, indicating nucleation controlled growth. Elevated deposition temperatures, on the other hand, render the CoSi2 formation process layer-by-layer which indicates enhanced nucleation of the CoSi2 and diffusion controlled growth. Our results further indicate that this observed trend is most likely related to stress and changes in microstructure introduced during reactive deposition of the CoSi film. The deposition temperature therefore provides a handle to tune the CoSi2 growth mechanism.

On the growth kinetics of Ni(Pt) silicide thin films

We report on the effect of Pt on the growth kinetics of δ-Ni2Si and Ni1−xPtxSi thin films formed by solid phase reaction of a Ni(Pt) alloyed thin film on Si(100). The study was performed by real-time Rutherford backscattering spectrometry examining the silicide growth rates for initial Pt concentrations of 0, 1, 3, 7, and 10 at. % relative to the Ni content. Pt was found to exert a drastic effect on the growth kinetics of both phases. δ-Ni2Si growth is slowed down tremendously, which results in the simultaneous growth of this phase with Ni1−xPtxSi. Activation energies extracted for the Ni1−xPtxSi growth process exhibit an increase from Ea = 1.35 ± 0.06 eV for binary NiSi to Ea = 2.7 ± 0.2 eV for Ni1−xPtxSi with an initial Pt concentration of 3 at. %. Further increasing the Pt content to 10 at. % merely increases the activation energy for Ni1−xPtxSi growth to Ea = 3.1 ± 0.5 eV.

Determination of the dominant diffusing species during nickel and palladium germanide formation

We have used real-time Rutherford backscattering spectrometry to determine the dominant diffusing species during the formation of nickel germanide and palladium germanide; two of the most promising candidates for use as ohmic contacts were germanium to replace silicon in devices. In the Ni/Ge system Ni5Ge3 is the first phase to form, followed by NiGe. The results show that during Ni5Ge3 formation Ni is essentially the sole diffusing species and is responsible for almost all the growth. During the 2nd-phase formation both Ni and Ge diffuse, with the Ge diffusion prominent during the very early stages, while the later stage of growth is dominated by Ni diffusion. During the formation of Pd2Ge and PdGe phases the metal (i.e. palladium) is once again the dominant diffusing species. The relative contribution of germanium diffusion to the growth is, however, more prominent in the Pd/Ge system, with significant amounts of Ge diffusion being observed during formation of both phases.

In situ study of the growth properties of Ni-rare earth silicides for interlayer and alloy systems on Si(100)

We report on the solid-phase reaction of thin Ni-rare earth films on a Si(100) substrate, for a variety of rare earth (RE) elements (Y, Gd, Dy, and Er). Both interlayer (Ni/RE/〈Si〉) and alloy (Ni-RE/〈Si〉) configurations were studied. The phase sequence during reaction was revealed using real-time x-ray diffraction whereas the elemental diffusion and growth kinetics were examined by real-time Rutherford backscattering spectrometry. All RE elements studied exert a similar influence on the solid phase reaction. Independent of the RE element or its initial distribution a ternary Ni2Si2RE phase forms, which ends up at the surface after NiSi growth. With respect to growth kinetics, the RE metal addition hampers the Ni diffusion process even for low concentrations of 2.5 at. %, resulting in the simultaneous growth of Ni-rich silicide and NiSi. Moreover, the formation of Ni2Si2RE during NiSi growth alters the Ni diffusion mechanism in the interlayer causing a sudden acceleration of the Ni silicide growth. Besides a significant effect on the silicide growth, we have found that adding 5 at. % Er (relative to Ni) lowers the NiSi Schottky barrier height on n-type Si(100) by approximately 0.1 eV for the interlayer and alloy configuration.

The influence of Pt redistribution on Ni1−xPtxSi growth properties

We have studied the influence of Pt on the growth of Ni silicide thin films by examining the Pt redistribution during silicide growth. Three different initial Pt configurations were investigated, i.e., a Pt alloy (Ni+Pt/⟨Si⟩), a Pt capping layer (Pt/Ni/⟨Si⟩) and a Pt interlayer (Ni/Pt/⟨Si⟩), all containing 7 at. % Pt relative to the Ni content. The Pt redistribution was probed using in situ real-time Rutherford backscattering spectrometry (RBS) whereas the phase sequence was monitored during the solid phase reaction (SPR) using in situ real-time x-ray diffraction. We found that the capping layer and alloy exhibit a SPR comparable to the pure Ni/⟨Si⟩ system, whereas Pt added as an interlayer has a much more drastic influence on the Ni silicide phase sequence. Nevertheless, for all initial sample configurations, Pt redistributes in an erratic way. This phenomenon can be assigned to the low solubility of Pt in Ni2Si compared to NiSi and the high mobility of Pt in Ni2Si compared to pure Ni. Real-time RBS further revealed that the crucial issue determining the growth properties of each silicide phase is the Pt concentration at the Si interface during the initial stages of phase formation. The formation of areas rich in Pt reduce the Ni silicide growth kinetics which influences the phase sequence and properties of the silicides.

Artificial neural networks for instantaneous analysis of real-time Rutherford backscattering spectra

Abstract This paper reports on the advantage of using artificial neural networks (ANNs) to analyze large sets of real-time Rutherford backscattering spectrometry (RBS) data. Real-time RBS, i.e. collecting RBS spectra at periodic time intervals during a thermal treatment, probes the full response of a thin film to the annealing in situ . Although very valuable insights can be gained by this technique, the time-consuming analysis of the vast amount of RBS spectra acquired during real-time RBS measurements has so far prevented the widespread use of real-time RBS. Setting up an ANN is quite an intensive process as well, but once trained, these ANNs can handle the analysis of large data sets practically instantaneously. As such, the beneficial combination of real-time RBS and ANN analysis forms a perfect synergy. In this test case, a network was trained and applied to analyze the Ni silicide growth during annealing of a thin 80 nm Ni film on Si(1 0 0). The ANN performance was validated by comparing the ANN results with the conventional analysis performed on the same data set.

Pt redistribution during Ni(Pt) silicide formation

We report on a real-time Rutherford backscattering spectrometry study of the erratic redistribution of Pt during Ni silicide formation in a solid phase reaction. The inhomogeneous Pt redistribution in Ni(Pt)Si films is a consequence of the low solubility of Pt in Ni2Si compared to NiSi and the limited mobility of Pt in NiSi. Pt further acts as a diffusion barrier and resides in the Ni2Si grain boundaries, significantly slowing down the Ni2Si and NiSi growth kinetics. Moreover, the observed incorporation of a large amount of Pt in the NiSi seeds indicates that Pt plays a major role in selecting the crystallographic orientation of these seeds and thus in the texture of the resulting Ni1−xPtxSi film.

In situ RBS analysis of CuInSe2

CuInSe2 thin films were prepared by sequential evaporation of the constituent elements onto Mo-coated glass substrates and the layers were subsequently selenized in a closed graphite box at 400°C. The films were characterised by X-ray diffraction (XRD) and in situ, real-time Rutherford backscattering spectrometry (RBS) analysis to monitor the progress of the reaction as the elemental layers interdiffused. For the Cu/In/Se structure, XRD performed after various anneals revealed that the Cu–In layer mixed with the Se layer to form a number of binary phases. For Cu/Se/In it was found that the Cu and Se had intermixed at room temperature. In both the structures investigated the Cu–Se and In–Se binary phases formed below 200°C and upon annealing above this temperature interdiffused to form chalcopyrite CuInSe2.

Thermal nitridation of silicon dioxide films

We have used real-time Rutherford backscattering spectrometry to determine the dominant diffusing species during the formation of nickel germanide and palladium germanide; two of the most promising candidates for use as ohmic contacts were germanium to replace silicon in devices. In the Ni/Ge system Ni5Ge3 is the first phase to form, followed by NiGe. The results show that during Ni5Ge3 formation Ni is essentially the sole diffusing species and is responsible for almost all the growth. During the 2nd-phase formation both Ni and Ge diffuse, with the Ge diffusion prominent during the very early stages, while the later stage of growth is dominated by Ni diffusion. During the formation of Pd2Ge and PdGe phases the metal (i.e. palladium) is once again the dominant diffusing species. The relative contribution of germanium diffusion to the growth is, however, more prominent in the Pd/Ge system, with significant amounts of Ge diffusion being observed during formation of both phases.