Multimethod System with XPS and INA-X (SIMS/SNMS)

As early as 10 years after the discovery of the giant magnetoresistance (GMR) the magnetic/non-magnetic multilayers found their first application in the read-out units of magnetic recording media, and the hard disk drives with GMR-based sensors since gained a dominating market share. In spite of the large number of works published on nanoscale multilayers, data on the depth profile of electrodeposited multilayer samples are very scarce. This work deals with the depth profile analysis of electrodeposited CoNiCu/Cu and Co/Cu multilayers films. Commercial Cu sheet and a Cr/Cu layer evaporated onto Si (1 1 1) surface were used as substrates with high and low roughness, respectively. The Secondary Neutral Mass Spectrometry (SNMS) depth profile analysis clearly revealed the layered structure of the samples. The resolution of the individual layers varied with the initial roughness of the substrate. The SNMS spectra showed that the oxygen incorporation into the layers is insignificant. When both Ni and Co are present in the magnetic layer, the composition of the samples is influenced by both the anomalous codeposition properties of the iron-group elements and the mass transport of the corresponding ions in the electrolyte. This observation draws the attention to the possible inhomogeneity of the magnetic layers in electrodeposited samples.

G. L. Katona, Z. Berenyi, L. Peter, K. Vad
Vacuum 82, pp. 270-273

It has long been known that a concentration gradient can develop in electrodeposits along the growth direction as a result of the combined impact of anomalous codeposition and mass trasnport limitation of the reactants. It is shown in the present paper that this composition change in electrodeposited Co–Ni–Cu/Cu multilayers can be verified by secondary neutral mass spectrometry (SNMS). Various electrodeposited samples have been analyzed and the resulting composition profiles have been compared to the calculation based on the non-destructive analysis of the overall composition. The change of the Co:Ni ratio in the magnetic layer along the growth direction has been verified. A calculation method has been proposed by which the local composition of the magnetic layer can be estimated from the thickness dependence of the overall multilayer composition. It has also been shown that the deviation of the experimental depth profile data from the estimation based on the variation of the total composition with the Co–Ni–Cu layer thickness can be ascribed to the roughness increase during the sputtering in the SNMS instrument.

L. Peter, G. L. Katona, Z. Berenyi, K. Vad, G. A. Langer, E. Toth-Kadar, J. Padar, L. Pogany, I. Bakonyi
Electrochimica Acta 53, pp. 837-845

Amorphous silicon materials and its alloys became extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry. Amorphous Si/Si1−xSbx/Si tri-layer samples with 5 at% antimony concentration were prepared by direct current magnetron sputtering onto Si substrate at room temperature. Annealing of the samples was performed at different temperatures in vacuum (p<10−7 mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent of diffusion, the evaluated diffusion coefficients are in the range of ∼10−21 m2s−1 at 550 °C.

A. Csik, G. A. Langer, G. Erdélyi, D. L. Beke, Z. Erdelyi, K. Vad
Acuum 82, pp. 257-260

Thermal annealing of Si/Si1−xSbx/Si amorphous thin-film tri-layer samples ( and 24 at%Sb) under 100 bar Ar pressure results in an interesting pattern formation. In pictures, taken by means of cross-sectional transmission electron microscopy, stripe-shaped contrast, with three maxima, parallel to the interfaces can be seen. Secondary neutral mass spectrometer measurements revealed that the regions with different contrasts correspond to Sb-rich and Sb-depleted regions. Furthermore, the Sb concentration peaks in the Sb-rich regions, especially at longer annealing times, are different: the peak developed at the Si/SiSb interface closer to the free surface decays faster than that of the inner one closer to the substrate. The pattern formation is interpreted by segregation-initiated spinodal-like decomposition, while the difference of the Sb concentration peaks is explained by the resultant Sb transport to and evaporation from the free surface. The possible role of formation of nanocrystalline grains, in the explanation of the fast transport under pressure as compared to vacuum is also discussed.

A. Csik, G. Erdélyi, G. A. Langer, L. Daróczi, D. L. Beke, J. Nyéki, Z. Erdélyi
Vacuum 80, pp.168-173

The design and the specification of the newly developed INA-X instrument for the electron-gas version of a secondary neutral mass spectrometer (SNMS) are described. A modified plasma chamber inside a UHV vessel in combination with optimized r.f. coupling enable a high plasma density at low power input. The ionization efficiency and the current density for sample sputtering are significantly improved compared to those of previous SNMS instruments. A novel detection optics allows us to define an energy window of 1–2 eV. The secondary neutral particle flux is collected under an oblique take-off angle against the surface normal, improving the quantifiability of the obtained SNMS spectra. The variable sputtering rate can be adjusted from some nm per min up to 1–2 μm per min, depending on the operator’s need, either to obtain high depth resolution or short analysis time. Examples for depth profiling of conducting and insulating films and coatings on the nano- and micrometer scales are presented.

J. Jorzick, J. Lösch, M. Kopnarski, H. Oechsner
Applied Physics A. 78, pp. 655-658

The design and the specifications of a prototype instrument for the electron gas version of secondary neutral mass spectrometry SNMS which will optionally enable measurements with X-ray induced photoelectron spectroscopy XPS, too, are described. By operating the SNMS plasma inside an ultra high vacuum vessel interfering signals from residual gas species are reduced to the level of the mass independent background. The influence of varying angular distributions of sputter-ejected neutrals at low ion energies for sample bombardment can be widely reduced by an oblique take-off for the postionized particles. First examples of SNMS-studies with the new system reveal a detection power well below 1 ppm. Analytically difficult elements as C or O become quantitatively detectable down to a level of several 10 ppm.

H. Oechsner, W. Bock, M. Kopnarski, M. Müller
Mikrochimica Acta 133, pp. 69-73