The influence of N content on the crystallization behavior of initially amorphous Ta-Si-N diffusion barriers deposited with a thickness of 10 nm between Cu and SiO 2 was investigated by means of glancing angle X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GD-OES), transmission electron microscopy (TEM), and graphite furnace atomic absorption spectrometry (GF-AAS) after annealing for various times at a temperature of T a n =600 o C. For a Ta 7 3 Si 2 7 film, only Ta silicide phases (Ta 5 Si 3 , Ta 2 Si) are formed, whereas all barriers containing nitrogen crystallize primarily into a Ta nitride. Si is not incorporated into this phase but diffuses mostly into the Cu film. Although the crystalline Ta nitride grows mainly within the original barrier region, it does not form a continuous layer. For barriers with a N content x N >=25 at.%, the annealing time necessary to start the crystallization increases and the formed Ta nitride phases become N-richer (Ta 2 N->Ta 5 N 6 ). A Ta 3 0 Si 1 8 N 5 2 layer maintains its amorphous structure even after annealing for t a n =100 h. With increasing N content in the barrier, the thermal stability against Cu diffusion is improved.