Role of High-k Interlayer in ZrO2/High-k/ZrO2 Insulating Multilayer on Electrical Properties for DRAM Capacitor

Abstract

For < 25 nm DRAM capacitors, large cell capacitance (20 fF/cell), low leakage current density (J ≤ 1.6×10-7 A/cm2) at the operation voltage (0.6 V), maximum process temperature < 650 oC and conformal films on a three-dimensional structure (pedestal structure) with a large aspect ratio over 30 are required. Recently, the ZrO2/Al2O3/ZrO2 (ZAZ) multilayer was widely used as insulator of DRAM.[1] Al2O3 has advantages of large band gap and amorphous structure, and disadvantage of low k-value. However, it is still not clear how amorphous structure and band gap of interlayer affect to leakage current property. Here, we pay attention to (Ta/Nb)Ox (TN) because of its high k-value (~29), amorphous structure and low band gap (4.3 eV).[2] In this paper, we studied role of various interlayer between ZrO2 layers on leakage current property for DRAM capacitors with TiN electrode. We fabricated four TiN capacitors with ZrO2/ZrO2 (ZZ), ZAZ, ZrO2/(Ta/Nb)Ox/ZrO2 (ZTNZ), and ZrO2/(Ta/Nb)Ox-Al2O3/ZrO2 (ZTNAZ) multilayer by atomic layer deposition (ALD) and post-deposition annealing (PDA) processes. The ZrO2, Al2O3, and TN layers were deposited by ALD using (C5H5)Zr[N(CH3)2]3, Al(CH3)3, and (Ta/Nb = 1/1)(NtAm)(NMe2)3 precursor, respectively, and H2O gas. The TNA nano-laminate layers were fabricated by alternately depositing every 1 cycle using TN and Al2O3. After multilayer fabrication, PDA was performed at 600 °C. Finally, TiN top electrode was fabricated by photo-litho. process. Fig. 1 shows relationship between CET and J at 0.6 V for all capacitors. The J values of the ZTNAZ and ZAZ capacitors decrease significantly by 10-7 ~ 10-8 A/cm2 order of magnitude while ZTNZ exhibits large J of ~ 10-5 A/cm2. Moreover, the J value of the ZTNAZ (CET = 1.2 nm) is lower than that of the ZAZ (CET = 1.3 nm). AFM images and RMS roughness of ZZ (CET = 1.1 nm), ZTNZ (CET = 1.2 nm), ZAZ (CET = 1.3 nm), and ZTNAZ (CET = 1.2 nm) are shown in Fig. 2. The RMS roughness of all samples exhibit almost the same value of around 1 nm. Based on these experimental data, we found that the leakage current property of capacitor is influenced by band gap width (conduction band offset of TiN) rather than amorphous structure. We conclude that the TNA is one of candidate material as interlayer for future DRAM. A part of this research is supported by CREST, JST. [1] D. Martin et al., J. Appl. Phys. 113, 194103 (2013). [2] T. Nabatame et al., J. Vac. Sci. Technol. A 33, 01A118 (2015). Figure 1