M. Moske

Texture and phase transformation of sputter-deposited metastable Ta films and Ta/Cu multilayers

Two different structures of Ta are known : the bulk bcc structure of α-Ta (a=0.33058 nm) and the metastable tetragonal β-Ta phase (a=0.534 nm, c=0.994 nm). The metastable phase is mainly observed in sputter-deposited thin films and a dependence on film thickness and deposition conditions have been reported. In our study we investigated the structure and the crystallographic orientation of d.c.-magnetron sputtered Ta films using wide-angle X-ray diffraction after preparation and after annealing. Ta films were deposited onto different underlayer materials (Al, SiO 2 and Cu). For Ta/Cu multilayers the single layer thickness and the sputter parameters are varied. It is observed that the Ta structure after deposition mainly depends on the substrate or underlayer material. β-Ta is always observed after sputtering onto SiO 2 or (111)-textured Cu, with the orientation of the Ta grains depending on the Ta-layer thickness, whereas α-Ta is observed on an (111)Al underlayer. Therefore, the bulk equilibrium phase only seems to be forced by an epitaxial relation. During annealing up to 700°C the (100)-oriented grains of β-Ta change their orientation and the metastable β-phase transforms into the equilibrium α-phase with (110) texture. The temperature for structural transformation decreases with increasing Ta layer thickness.

Amorphous thin-film growth: Theory compared with experiment

Experimental results on amorphous ZrAlCu thin-film growth and the dynamics of the surface morphology as predicted from a minimal nonlinear stochastic deposition equation are analysed and compared. Key points of this study are: i) an estimation procedure for coefficients entering into the growth equation and ii) a detailed analysis and interpretation of the time evolution of the correlation length and the surface roughness. The results corroborate the usefulness of the deposition equation as a tool for studying amorphous growth processes.

Determination of the Height-Height Correlation Function of Rough Surfaces from Diffuse X-Ray Scattering

We show that the height-height correlation function of a rough surface can be determined from the diffuse x-ray scattering intensity by an explicit back-transformation without any model assumptions. This is in contrast to the conventional fitting procedure of the data with parameterized correlation functions. The method is illustrated by the example of an amorphous Zr35Co65 film evaporated on a silicon substrate with native oxide. The height-height correlation function obtained from the diffuse-scattering data is compared to the result of in situ STM measurements.

Kohlrausch exponent of amorphous Zr65Al7.5Cu27.5 determined by anelastic relaxation measurements

Anelastic relaxations of amorphous Zr65Al7.5Cu27.5 have been studied in the range of the glass transition and in the supercooled liquid. Applying a force step function, an anelastic aftereffect of the form exp(t/τ)β (Kohlrausch–Williams–Watts function) is expected with an exponent β<1. From the measurement a value of β=0.67±0.03 is determined at Tg which confirms the empirical correlation between the fragility index m (36.4 for Zr65Al7.5Cu27.5) and β, established by Bohmer et al. This result is another indication for the metallic glass Zr65Al7.5Cu27.5 being a rather strong glass former. Furthermore, a strong increase in β just above Tg is found and is interpreted in the framework of a cluster model.

The role of particle energy and pulsed particle flux in physical vapor deposition and pulsed–laser deposition

Surface morphology evolution of thin films generated by physical and pulsed-laser deposition depending on the incident particle energy and the pulse rate is investigated using a continuum growth model. The model includes curvature-induced surface diffusion, the Schwoebel barrier and surface atom displacement as main surface processes. The numerical solution of the model is in very good agreement with the results of kinetic Monte Carlo simulations, which also serve to estimate the continuum growth parameters, and with experimental results on thin Si films. The increase of the incident particle energy, starting from thermal energy, fundamentally influences the surface topography, changing from self-affine to self-organized morphology.

Surface topography of amorphous Zr65.0Al7.5Cu27.5 alloy films around the glass transition–an in-situ UHV-STM study

Abstract The ternary metallic glass Zr 65.0 Al 7.5 Cu 27.5 shows a wide supercooled liquid region above the glass transition temperature T g , which enables extended structural investigations of the undercooled liquid. Thin films of this alloy have been prepared by electron beam deposition in ultra high vacuum onto thermally oxidized silicon substrates at room temperature. For the first time the surface morphology of these films has been investigated in situ with scanning tunnelling microscopy (STM). We have recorded STM topographs after different annealing stages, representing the evolution of the surface at elevated temperatures. The change in surface structure is discussed with respect to structural relaxation behaviour and viscous flow properties of the films.

Structural, magnetotransport, and micromagnetic properties of sputtered Ir(111)/Co superlattices

This article presents a further study on the structural and magnetotransport properties in sputtered Ir(111)/Co superlattices. The magnetization loops and magnetoresistance curves show a correlation, which can be written as ΔR/R∝−(M/Ms)2 and indicates that the resistive change in external magnetic field is due to spin dependent scattering of conduction electrons, although the largest ΔR/R value observed is only 4% (10 K). The low effect can be attributed to band matching between Ir and Co subbands. Annealing effects on structural and magnetic properties were observed by the results that interdiffusion of the components takes place at an annealing temperature above 350 °C and leads to degradation of the superlattice, followed by a decrease both in magnetic moment and in magnetoresistance. The images of Kerr microscopy and magnetic force microscopy show micromagnetic structures, which can be well understood in comparison with the magnetization and magnetoresistance measurements.

Investigation on metallurgical properties and electromigration in AlCu metallizations for VLSI applications

Abstract The purpose of this study is to investigate the correlations between the deposition parameters, the resulting metallurgical properties, and finally the electromigration resistance of AlCu alloy films and line structures of different compositions and different multilayer sequences. The alloy films were either sputtered onto a physical vapour deposition Ti TiN diffusion barrier, or for selected samples, directly on the boron phosphorus silicon glass base layer. We investigated AlCu alloy films with 0.5, 1.0 and 2.0 at.% Cu content in comparison with the standard metallization AlSi 1.0 Cu 0.5 used by Siemens, as a reference. For all alloy films investigated, the multilayer sequence is varied and the resulting properties are characterized afterwards. The results are compiled in a metallurgical data base with the following physical characterization properties: layer thickness, grain size, microhardness, wafer bow, optical surface reflectivity, and electrical resistivity. For selected samples electromigration tests, X-ray diffraction texture analysis, Auger electron spectroscopy, energy dispersive X-ray analysis, and scanning electron microscopy are applied. With the support of this data base we are able to obtain information about the correlation between microscopic and macroscopic properties of the investigated metallizations and multilayer structures, and especially about the specific influence on their electromigration resistance.

Giant magnetoresistance and interlayer coupling in Cu(111)/Ag67Co33 granular multilayers

Cu/AgCo layered granular structures were prepared to study their field transport properties in comparison to their microstructure. The superlattices of the samples were characterized by x-ray diffraction. A combination of random and antiparallel alignments of magnetic particles is discovered expressing an oscillation of interlayer coupling similar to conventional multilayers. The weak antiferromagnetic coupling across thin Cu spacer layers between interfacial Co particles results in a notable enhancement of low-field sensitivity compared to granular single films. The oscillation period obtained here for Cu(111) interlayers is close to 3 atomic layers.

Magnetization and magnetoresistance in granular AgCo films

Abstract A series of 150 nm thick Ag100 − xCox films (x varying from 12 at.% to 46 at.%) were grown by e-beam coevaporation in an UHV system at substrate temperatures, Ts, between 30 °C and 200 °C, followed by a heat treatment. For the analysis of the magnetic properties of the Co precipitates we fit our m(B) measurements with a log-normal distribution of radii using the Langevin function to obtain mean radii of the superparamagnetic particles. By annealing it is possible to optimize the giant magnetoresistance Δρ ρ of samples grown at room temperature, whereas no heat treatment seems to be necessary for samples evaporated at elevated temperatures. These magnetic film properties are compared with the corresponding Co particle sizes and size distributions. The film structure and morphology was determined ex situ by X-ray diffraction. Our results of the magnetic film properties are consistent with the observed changes in microstructure and Co particle growth.