Diffusion barriers for Cu metallisation in Si integrated circuits: deposition and related thin film properties

In modern integrated circuits with Cu interconnects a diffusion barrier is used between the dielectric and Cu in order to prevent diffusion of Cu through the dielectrics. The choice of such a barrier requires a material exploration and a study of the material reactivity with both Cu and the dielectric used in the back-end processing. This thesis presents results of a study focused on the growth processes of tungsten nitride silicide films by CVD; tungsten nitride and tungsten carbidonitride films by ALD. The suitability of these materials as a diffusion barrier has also been evaluated by testing film properties such as resistivity, RMS-roughness, the reactivity with Cu, blocking properties to Cu diffusion and adhesion. A combination of Cu and the tungsten silicide nitride with a Si to W ratio ≥0.8 has shown Si diffusion out of the barriers into Cu resulting in a large increase of Curesistivity. Thus, these materials failed the criterion of low reactivity with Cu, which has been tested with four-point probe in situ sheet resistance measurements at elevated temperatures. Tungsten nitride and tungsten carbonitride films are shown to have low reactivity with Cu. Moreover, good blocking properties of these films against Cu and Al diffusion have been demonstrated on capacitors and p+/n diodes.