Effect of oxygen on the reactions in the Si/Ta/Cu metallization system

The effect of oxygen on the reaction mechanisms in the Si/Ta/Cu metallizati on system was studied experimentally and by utilizing the thermodynamically assessed Ta-O binary system. It was presented that an interfacial tantalum oxide was formed between Cu and Ta and that it established an additional b arrier layer for Cu diffusion. The formation of additional barrier layer wa s supported by the following observations: (i) No detectable amount of Cu w as found from the Ta layer with the combined transmission electron microsco py and energy dispersive spectroscopy at temperatures as high as 650 degree sC. (ii) Secondary ion mass spectrometry measurements indicated that signif icant amount of oxygen was incorporated into the films already after the sp uttering stage. (iii) (TaO)-Ta-181-O-16 molecular ion signals were detected from the Ta/Cu interface, indicating that the additional layer was in fact some form of tantalum oxide. The diffusion of Cu through the Ta layer coul d not proceed until the interfacial oxide had been dissolved by the Ta matr ix. Since the oxygen solubility in Ta matrix is high in the temperature ran ge of interest, the interfacial oxide dissolution was kinetically controlle d. It is to be noted that the threshold temperature range of the dissolutio n reaction was found to coincide with that of the beta -Ta to the bcc-Ta tr ansition, which was anticipated to enhance the kinetics of the dissolution.