Marker studies of the solid state formation of CrSi2 on Pd2Si

Abstract

The chemical system, Si < >1 Pd 1Cr, was investigated to study the formation of CrSil on polycrystalline PdlSi, formed on Si<IOO> and epitaxial PdlSi formed on Si<lll>. To ascertain the reaction mechanism during the formation, tantalum was used as an inert marker, since it does not participate in the reaction and is readily measured by Rutherford Backscattering Spectrometry (RBS). This investigation was performed in two parts. In the first part, the tantalum was inserted in the PdlSi layer to determine which species; palladium or silicon diffuses during CrSil formation. In the second part, the marker was inserted in the CrSiI layer to determine whether chromium or silicon moves. In addition, the effect of marker thickness on the growth of CrSiI was investigated. The samples were prepared by electron gun evaporation in vacuum, the elements being deposited on the particular silicon substrates. This was followed by the thermal treatment of the samples at temperatures of 400,425,450,475,500 and 550°C. Normal and dynamic Rutherford backscattering spectrometry was used to characterize the thin film structures. If the marker, when inserted in the PdISi layer, should move towards the PdISi I CrSil interface then, the formation of CrSil would be due to the dissociation of Pd2Si. In this case PdlSi dissociates into Pd and Si and the Si diffuses to the interface of CrSi2 and Cr to form CrSil, whereas the Pd diffuses to the Si < > I Pd2Si interface to regrow PdISi. However, if the marker position remains constant with respect to the Pd2Si layer it can be concluded that the formation of CrSiI is due to the movement of Si from the substrate to the interface of CrSi2 and Cr to form CrSiI. If the marker when inserted in the CrSi2 should move towards the sample surface then the chromium diffuses to the interface ofCrSi1 and PdlSi to react with the silicon, forming CrSi2 .