A Study on Pt/Al Reaction Mechanism in the FeRAM Device Integration

Abstract

The capacitor contact barrier(CCB) layers have been introduced in the FeRAM integration to prevent the Pt/Al reaction during the back-end processes. Therefore, the interdiffusion and intermetallic formation in <TEX>$Pt(1500{\AA})/Al(3000{\AA})$</TEX> film stacks were investigated over the annealing temperature range of <TEX>$100\sim500^{\circ}C$</TEX>. The interdiffusion in Pt/Al interface started at <TEX>$300^{\circ}C$</TEX> and the stack was completlely intermixed after annealing over <TEX>$400^{\circ}C$</TEX> in nitrogen ambient for 1 hour. Both XRD and SBM analyses revealed that the Pt/Al interdiffusion formed a single phase of <TEX>$RtAl_2$</TEX> intermetallic compound. On the other hand, in the presence of TiN(<TEX>$1000{\AA}$</TEX>) barrier layer at the Pt/Al interface, the intermetallic formation was completely suppressed even after the annealing at <TEX>$500^{\circ}C$</TEX>. These were in good agreement with the predicted effect of the TiN diffusion barrier layer. But the conventional TiN CCB layer could not perfectly block the Pt/Al reaction during the back-end processes of the FeRAM integration with the maximum annealing temperature of <TEX>$420^{\circ}C$</TEX>. The difference in the TiN barrier properties could be explained by the voids generated on the Pt electrode surface during the integration. The voids were acted as the starting point of the Pt/Al reaction in real FeRAM structure.