Integrity of copper-tantalum nitride metallization under different ambient conditions

The integrity of the Cu/IMP Ta2.3N metallization under different annealing ambients has been investigated by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), X-ray diffractometry (XRD), Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. Results from XRD and TEM show that the as-deposited amorphous Ta2.3N barrier crystallizes upon annealing at 500°C, forming a Ta2N crystalline phase. The sheet resistance of Cu/Ta2.3N metallization remains unchanged upon annealing in Ar or N2 up to 750°C. No observable interdiffusion was detected by RBS upon annealing at temperatures below 500°C in Ar or N2. However, above 500°C, the integrity of Cu/Ta2.3N metallization begins to degrade due to out-diffusion of a small amount of Ta into Cu. On the other hand, in an N2/20% O2 ambient, the sheet resistance of the metallization is found to increase drastically upon annealing at a temperature above 200°C, an observation that has been attributed to the formation of porous Cu oxide layer. Delamination of Cu oxide from oxide/barrier interface occurs at 400°C. The result highlights the importance of isolating Cu/Ta2.3N metallization from oxygen exposure during back end processing.