Diffusion in thin Al/Cu/Fe films at different annealing temperatures was investigated. X-ray diffraction and Auger spectroscopy methods showed that mutual diffusion of elements occurs during annealing, leading to the formation of intermetallic compounds.
When annealing Al/Cu films, the formation of the intermetallic compound CuAl2 is observed, the rate of formation of which increases with increasing temperature. In the case of Al/Fe films, the intermetallic compound FeAl3 is formed, and the diffusion of iron into aluminum occurs faster than the diffusion of aluminum into iron.
The introduction of an additional layer of copper between aluminum and iron slows down the diffusion of iron into aluminum and promotes the formation of a more homogeneous structure. The results obtained can be used to optimize technological processes in the production of microelectronic devices.
The ternary Al–Cu–Fe system attracts attention due to its quasicrystalline phase with the composition Al62.5Cu25Fe12.5. One way to create homogeneous films is a two-stage process involving multilayer deposition followed by heat treatment. It is important not only to accurately select the thickness of each layer, but also to ensure sufficient homogenization during annealing. Therefore, studying the evolution of the depth profile from a multilayer structure to a homogeneous film is of particular interest. Auger electron spectroscopy (AES) and Rutherford backscattering spectrometry (RBS) are often used for depth profiling.
Diffusion in heat-treated bilayers has been studied in detail in a number of papers. There are many publications devoted to Al/Cu bilayers, including in the context of VLSI studies. In addition to bilayers, thin Cu films on an Al substrate have been studied, as well as contact samples. A detailed description of the phase formation sequence as a function of the Al:Cu atomic ratio is presented by Vandenberg and Hamm.
Various layer sequences were created. The main focus was on the Al/Cu/Fe/substrate trilayer materials. Al/Cu/substrate, Al/Fe/substrate and Cu/Fe/substrate bilayers were also used. The total thickness of all thin-film structures was about 300 nm and was chosen to obtain optimal CPOP spectra.
The sequence of layers was chosen taking into account practical application. It is desirable that the top layer be aluminum, as it forms a protective layer in an oxygen environment. When applied to steel substrates in future experiments, it is advisable to place iron next to the substrate to improve adhesion.
Author: M. Čekada, P. Panjan, J. Dolinšek, A. Zalar, Z. Medunić, M. Jakšić, N. Radić
Institute: Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia, Ruđer Bošković Institute, Bijenička 54, POB. 180, 10002 Zagreb, Croatia