Failure analysis of nanocrystals embedded high-k dielectrics for nonvolatile memories

Abstract

Semiconducting and metallic nanocrystals have been embedded in high-k dielectrics for nonvolatile memories for advantages of low leakage currents, large charge storage capacities, and long retention times. However, there are few studies on the reliability issues, such as the breakdown mechanism and relaxation current decay rate. In this paper, authors investigated the reliability of four different kinds of nanocrystals, i.e., ruthenium, indium tin oxide, silicon, and zinc oxide, embedded in the Zr-doped HfO2 high-k thin film. Although all nanocrystals embedded samples have charge storage capacity about one order of magnitude higher than that without nanocrystals embedded samples, the formerpsilas relaxation currents are higher and decay times are longer than those of the latter. When the relaxation currents were fitted to the Curie-von Schweidler law, the formerpsilas n values were between 0.4 and 0.65, which are different from the latterpsilas n values of near 1. When the naocrystals embedded sample was broken under a high bias gate voltage stress, the high-k part failed while the nanocrystals remained unattacked. This is demonstrated by the lack of polarity change of the relaxation current. The time to breakdown of the high-k film was also extended due to the inclusion of nanocrystals in the film. Therefore, the embedded nanocrystals play an important role for the reliability of this kind of nonvolatile memory device.