MS-3-P-2205 Structural features contributing to electrical resistivity in Cu-Mn alloy films

The fast development of the electronic industry raises the need of development faster and smaller devices. Consequently, the elements of the integrated devices become smaller and smaller. This, however, puts stringent demands on the contacts and interconnects. Around the presently used copper contacts a barrier layer must be manufactured which prevents the interdiffusion of copper into the dielectric materials. Utilization of self-organized barrier layers can provide a new solution to this problem. Cu-Mn alloy films as barrier layers appear a promising material for future technologies.

The aim of this research is to build a comprehensive view of the phases, structures and morphologies occurring in the Cu-Mn thin film system as well as their scattering mechanisms giving different contribution to the electrical resistivity of the films.

Eleven films, 1 μm thick, were grown at room temperature by DC magnetron sputtering covering the whole concentration interval. Then the electrical resistivity was measured as the function of composition by van der Pauw method. The results were correlated with the films structure studied by TEM.

The electrical resistivity of the films varied between 1.7 and 205 μΩcm and except of two concentration intervals it showed linear dependence on Mn concentration. Utilizing these results the whole alloy region was divided into five parts. Three single-phase regions were identified. Below 20 at% Mn content an fcc solid solution of Mn in Cu exists, in the 40-70 at% Mn interval the structure is an amorphous alloy, and finally above 80 at% Mn an α-Mn based solid solution forms. Two-phase regions exist in the concentration regions between the single-phase ones: at Mn concentrations between 20 and 40 at% the fcc solid solution and amorphous phases are present, while in the interval 70-80 at% Mn the amorphous phase and the α-Mn based solid solution keep balance with each other (Fig. 1.).

The resistivity measurements and the structural information obtained by TEM were used for modelling the conduction mechanisms in the films. In the model, the experimental resistivity was described as the sum of the resistivity due to different scattering mechanisms (Mathiessen rule). As a result, we could conclude, that in the fcc solid solution region and in the amorphous structures the resistivity is influenced by thermal and solute (Nordheim) scattering. In the two-phase regions and in the Mn-based solid solution region in addition to the above scattering mechanisms the grain boundary scattering contributes significantly. In the concentration regions, where the contribution of solute scattering is important Moiij correlation (high resistivity and small negative TCR) was also observed. (Fig. 2.)