MS-3-P-2213 Relation between surface and internal structure of Cu-Mn thin films

In semiconductor industry with the scaling down of ultra large integrated circuits the idea of self-forming barriers emerged. Cu-Mn alloys have been found a perspective binary alloy system for this purpose. For barrier layers beside excellent diffusion barrier property various other requirements exist such as low resistivity and good adhesion strength. Since surface morphology has considerable effect on both properties the investigation of the interrelation between surface and internal structure is of outmost importance.
The aim of this research is to systematically study the effect of microstructure on the surface morphology as a function of composition in a thin film system. For this purpose TEM, SEM and AFM techniques were used for determining the morphology, phases and surface roughness of the films.
Cu-Mn films of 50 nm thickness were co-deposited by DC magnetron sputtering. For TEM investigations TEM grids coated with carbon film were used while for surface characterisations films were grown on Si/SiO2 substrate. We used combinatorial method to obtain a comprehensive view of properties in the whole composition range of the alloy. Compositional gradient within one sample was achieved by shadowing atomic fluxes using a special experimental setup (Fig.1). The composition gradient was verified by EDS line scan. The size of coherently scattering regions interpreted as grain size was determined from line broadening of electron diffraction peaks.
The combinatorial method makes possible to map the morphological and phase properties in continuously changing composition gradient films and to conclude how these characteristics are interrelated with the structure and growth mechanisms of the film.
We could establish that with varying composition the phase state can change from one phase to two phase material and from crystalline to amorphous. This brought about smoother films for two phase films, when crystal growth during film development was limited by the formation of a second phase. The quantitative relation between lateral and vertical surface features and internal morphologic parameters is evaluated. The variation of internal structure is in accordance with the variation of surface roughness and morphology (Fig. 2). Grain size has strong correlation with the roughness of the films; smaller grains result in smoother surfaces (Fig. 3). Consequently, the lowest roughness values were measured in the amorphous region. The contribution of surface morphology and roughness in the electrical properties will also be discussed in accordance with the phase and internal structure of the films.