3 years ago

Improved leakage current properties of ZrO2/(Ta/Nb)Ox-Al2O3/ZrO2 nanolaminate insulating stacks for dynamic random access memory capacitors

Toyohiro Chikyow, Tomomi Sawada, Takashi Onaya, Kazunori Kurishima, Akihiko Ohi, Atsushi Ogura, Toshihide Nabatame, Naomi Sawamoto
The influence of amorphous high-k interlayers, such as Al2O3, (Ta/Nb)Ox (TN), and (Ta/Nb)Ox-Al2O3 (TNA), on the leakage current (J) and dielectric constant (k) for metal-insulator-metal capacitors with ZrO2/high-k/ZrO2 nanolaminate insulating films and TiN electrodes was investigated. The insulating films were prepared by atomic layer deposition followed by post-deposition annealing at 600 °C. The capacitance equivalent thickness (CET) of the capacitors increased in the order ZrO2/(Ta/Nb)Ox/ZrO2 (ZTNZ) < ZrO2/(Ta/Nb)Ox-Al2O3/ZrO2 (ZTNAZ) < ZrO2/Al2O3/ZrO2 (ZAZ), owing to the k values for Al2O3 (~6), TNA (~9), and TN (~11). The J values at 0.6 V for capacitors with a CET of 1.1 nm increased in the order ZTNAZ < ZAZ ≪ ZTNZ. The effect of a high-k interlayer on the J characteristics appeared above a thickness of 0.4 nm in the case of Al2O3 and TNA, while a 0.8-nm-thick TN maintained high J values. Based on these results, there are three important factors as a high-k interlayer to reduce J value, such as a band gap larger than that for TN (4.4 eV), a thickness of ≥0.4 nm, and an amorphous structure. Therefore, to achieve the low J and CET, TNA is a promising candidate material for a high-k interlayer for future dynamic random access memory.
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