Rare earth oxide capping effect on La₂O₃ gate dielectrics for equivalent oxide thickness scaling toward 0.5nm

The capping La₂O₃ gate dielectric with rare earth oxide (Ce, Pr, Nd, and Tm oxides) and the influence of rare earth oxides on the interface reaction have been examined and the electrical characteristics have been evaluated. The formation of Si-rich silicate phase in the interfacial silicate layer have been suppressed with Nd and Tm oxide cappings, presumably owing to the reduced generation rate of radical oxygen atoms in the cappings. Therefore, Nd and Tm oxide capping has advantage in scaling the equivalent oxide thickness owing to the increase in the average dielectric constant with reduced leakage current. On the other hand, Ce-and Pr-oxide cappings have shown no appreciable influence on the interfacial reaction to that without capping. However, with Ce-oxide capping, positively charged fixed defects created in smaller equivalent oxide thickness (EOT) can be well suppressed owing to the valence number fluctuation properties. Although capacitors and transistors with the rare earth cappings have shown the same degradation tendency along with the equivalent oxide thickness, Nd or Tm capping is one of the promising candidates for scaling device with La₂O₃.