Ion beam induced surface and interface engineering

Rutherford backscattering spectrometry (RBS) and related techniques have long been used to determine the elemental depth profiles in films a few nanometres to a few microns thick. However, although obtaining spectra is very easy, solving the inverse problem of extracting the depth profiles from the spectra is not possible analytically except for special cases. It is because these special cases include important classes of samples, and because skilled analysts are adept at extracting useful qualitative information from the data, that ion beam analysis is still an important technique. We have recently solved this inverse problem using the simulated annealing algorithm. We have implemented the solution in the `IBA DataFurnace' code, which has been developed into a very versatile and general new software tool that analysts can now use to rapidly extract quantitative accurate depth profiles from real samples on an industrial scale. We review the features, applicability and validation of this new code together with other approaches to handling IBA (ion beam analysis) data, with particular attention being given to determining both the absolute accuracy of the depth profiles and statistically accurate error estimates. We include examples of analyses using RBS, non-Rutherford elastic scattering, elastic recoil detection and non-resonant nuclear reactions. High depth resolution and the use of multiple techniques simultaneously are both discussed. There is usually systematic ambiguity in IBA data and Butler's example of ambiguity (1990 Nucl. Instrum. Methods B 45 160–5) is reanalysed. Analyses are shown: of evaporated, sputtered, oxidized, ion implanted, ion beam mixed and annealed materials; of semiconductors, optical and magnetic multilayers, superconductors, tribological films and metals; and of oxides on Si, mixed metal silicides, boron nitride, GaN, SiC, mixed metal oxides, YBCO and polymers.

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Elemental thin film depth profiles by ion beam analysis using simulated annealing - a new tool

TOPICAL REVIEW: Elemental thin film depth profiles by ion beam analysis using simulated annealing - a new tool

Knowledge on the thickness, composition, and interfaces of thin films and multilayers is, in many systems, fundamental for the understanding and optimization of their properties. One of the techniques often applied to such studies is Rutherford backscattering (RBS). However, it has been very difficult to account for the effects of interface roughness in the data obtained, and the alternative has been to develop dedicated data analysis codes for particular problems where roughness plays a determinant role. In this work, the effect of roughness is taken into account in the data analysis by calculating the effect of roughness on the apparent energy resolution as a function of depth. This depends on the exact type of roughness, and three different models have been implemented: inhomogeneous layer thickness, corrugated sample, and rough substrate surface. Interfacial mixing in multilayers can also be analysed with the method developed. Automatic fits to the data can be performed in this way, where the roughness parameters are derived during the fit, providing a new tool for RBS analysis. The code is applied to several systems in order to test its validity and applicability. Systems which are hard to analyse by RBS have been chosen: Si/VS/ Si0.65 Ge0.35 300 nm/ Si0.2 Ge0.8 4 nm/ Si0.65 Ge0.35 15 nm/Si 3 nm thin films, where VS stands for a linearly composition-graded virtual substrate; and MgO /( Fe 25 A/ Co 20 A)10 multilayers.

https://iopscience.iop.org/article/10.1088/0022-3727/34/14/305/pdf

Rutherford backscattering analysis of thin films and superlattices with roughness

The growth of Si1-xGex quantum wells with high Ge composition (x>0.5) on Si(001) substrates by MBE is of great interest both for HMOS device applications and fundamental research. One of the possibilities to obtain a high Ge content Si1-xGex channel for mobile carriers, while retaining its strain, is to grow a relaxed Si1-yGey buffer layer on an underlying Si substrate. Such a buffer is termed a virtual substrate (VS), which is a constituent of SiGe metamorphic heterostructures. The effect of annealing on the structure of the Si(001)/VS/Si0.7Ge0.3/Si0.2Ge0.8/Si0.7Ge0.3 heterostructures was studied by grazing angle of incidence RBS. The thickness of the Si0.2Ge0.8 channel is inhomogeneous, which makes the analysis of the data by traditional means very hard. We have developed a model whereby the influence of the thickness inhomogeneity of each layer in the apparent energy resolution as a function of depth can be calculated. Automatic fits to the data were performed, and the roughness parameters, that is, the standard deviation of the thickness inhomogeneity of the relevant layers, were obtained, together with the thickness and stoichiometry of each layer. The results are compared with TEM and high resolution XRD experiments.

RBS ANALYSIS OF MBE GROWN SiGe/(001)Si HETEROSTRUCTURES WITH THIN HIGH Ge CONTENT SiGe CHANNELS FOR HMOS TRANSISTORS

We report on the room-temperature synthesis of the low-resistivity TaSi2 phase using ion-beam mixing of Ta/Si bilayers with Ar ions. The formation of the silicide phase is observed for different damage energies deposited at the Ta/Si interface. The variance Δσ 2 of the reacted (TaSi2) layer thickness varies linearly with the ion fluence Φ and the reaction rate Δσ 2 /Φ is proportional to the deposited damage energy density FD. The measured mixing/reaction efficiency, Δσ 2 /ΦF D =10±1 nm5/keV, is in agreement with the value calculated by the model of compound formation under local thermal spikes.

Interface mixing in Ta/Si bilayers with Ar ions

Nitrides, carbides and oxides are important ceramic materials for wide range of applications in coating, nuclear reactor and semiconductor technology The study of their bonding properties to metals and semiconductors, for instance via ion irradiation, is of great importance In this work, we report on the effects induced by 100 and 450 keV Xe+ ions in 70–100 nm Ni3N layers deposited on Si substrates Low-energy irradiation at 80 K was found to cause a preferential nitrogen loss in the near-surface regions and an increase in surface roughness of the Ni3N film After the 450 keV Xe+ ion irradiation, strong mixing and the formation of Ni2Si and Si3N4 phases were detected at the Ni3N/Si interface These findings demonstrate the dissociation of Ni3N under ion bombardment and the competition of chemical driving forces and collision cascade mixing at the interface

Ion-beam irradiation effects on Ni3N/Si bilayers

The article reports on the Xe ion beam irradiation studies of Ni3N/Al bilayers at 80 K. The ion-induced modifications were monitored by Rutherford backscattering (RBS), resonant nuclear reaction analysis (RNRA), X-ray diffraction (XRD) and atomic force microscopy (AFM). We found preferential loss of nitrogen from the surface region of the Ni3N top layers. The surface roughness ΔσS and the interface broadening variance Δσint2 increase linearly with the Xe ion fluence Φ. The experimental mixing rate of Δσ 2 /Φ=1.8 nm 4 is explained by considering an enhancement of ballistic mixing due to chemical reactions at the interface.

L. Rissanen

Papers

Interface mixing in Ta/Si bilayers with Ar ions

Ion-beam irradiation effects on Ni3N/Si bilayers

Heavy ion irradiation induced effects in Ni3N/Al bilayers