1 中国科学院苏州纳米技术与纳米仿生研究所，纳米真空互联实验站，江苏 苏州 2151232 中国科学技术大学纳米科学与技术学院，合肥 2300263 无锡拍字节科技有限公司，江苏 无锡 2140284 Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, OK 74104, USA
1. Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu Province, China;2. Nano Science and Technology Institute, University of Science and Technology of China, Hefei 230026, China;3. Wuxi Petabyte Technology Co. Ltd., Wuxi 214028, Jiangsu Province, China;4. Department of Physics and Engineering Physics, The University of Tulsa, Tulsa, OK 74104, USA
Abstract:
HfO2-based ferroelectric capacitors, particularly TiN/HfxZr1-xO2/TiN metal insulator metal (MIM) capacitors, have attracted considerable attention as promising candidates in the new generation of nonvolatile memory applications, because of their excellent stability, high performance, and complementary metal oxide semiconductor (CMOS) compatibility. At the electrode interface of TiN/HfxZr1-xO2/TiN MIM ferroelectric devices, the existence of the TiOxNy layer, which was formed during HfxZr1-xO2 film crystallization and TiN oxidization, can affect interface/grain boundary energy, film stress, and conduction band offset at the TiN/HfxZr1-xO2 interface, thereby affecting the ferroelectric device performance. Because the electrical performance of TiN/HfxZr1-xO2/TiN capacitors depends on both the ferroelectric HfxZr1-xO2 thin films and electrode TiN/insulator HfxZr1-xO2 interface, it is essential to control the fabrication of the TiN/HfxZr1-xO2/TiN heterostructure. Herein, we report a new method for preparing HfxZr1-xO2 ferroelectric thin films, sandwiched between TiN electrodes, by atomic layer deposition (ALD) and using ultra high vacuum (UHV) sputtering equipment interconnected with an ultra-high vacuum system. The quasi in situ characterization by transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and other analytical methods conducted in our study indicates that the surface of the bottom TiN electrode does not contain oxygen. Moreover, a flat signal for impurities at the interface suggests that the superior ferroelectric performance of HfxZr1-xO2-based device is mainly attributed to the pristine HfxZr1-xO2/TiN interface. Furthermore, the ferroelectric properties of TiN/HfxZr1-xO2/TiN heterostructures on silicon can be modulated by varying ZrO2 doping concentration and rapid thermal annealing (RTA) temperature, which can be well monitored and controlled by the interconnected system. We also investigate the ferroelectric properties of TiN/HfxZr1-xO2/TiN capacitors with different ZrO2 doping concentrations (30%–60% (x)) at room temperature by changing the ALD pulsing ratio within the vacuum interconnected system. Three identical 10 nm-thick Hf0.5Zr0.5O2 samples sandwiched between TiN electrodes are annealed in N2 ambient at 400, 450 and 600 ℃ for 5 min to investigate the effect of RTA on device performance. The evolution of P-E hysteresis at different applied voltages and RTA temperatures reveals that the saturation of P-E hysteresis and remanent polarization increase with RTA temperature. This increase is especially evident at low applied voltages such as 1.5 V. A higher remanent polarization of 21.5 μC·cm-2 than the previously reported value and a low coercive voltage of 1.35 V were achieved for the electric field of 3 MV·cm-1 by doping 50% (molar fraction, x) ZrO2 in HfO2 through RTA at 600 ℃ for film crystallization.
