MESA+ Institute for Nanotechnology

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 the tungsten silicide nitride with Si to W ratio ≥0.8 and Cu has shown Si diffusion out of the barriers into Cu resulting in a large increase of Cu-resistivity. 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.

At the same time a continuous scaling of components in IC’s demands the integration of low-k dielectrics, e.g. SiLKTM (an aromatic hydrocarbon based polymer with a static dielectric constant ~2.65), in a back-end process of IC’s. This requires a study of processes at the interface of the dielectric film with Ta-based materials, which are used conventionally as barriers. Therefore a study of the interaction of SiLK with the Ta-based materials has been performed. Sheet resistance measurements show that tantalum nitrides containing 8-10 at% N have better thermal stability on SiLK than pure Ta films. The four point bend test shows suitable adhesion. No reaction of hydrocarbons from SiLK with Ta-based barriers, which results in tantalum carbide formation, has been observed.