A comparative study of metal-ferroelectric-metal devices using doped- and stacked-hafnium zirconium oxides
Introduction
Compared to the traditional flash memory, the ferroelectric random access memory with potential device performances such as emerging non-volatile property, fast switching speed, low power consumption, and long endurance cycling has attracted more attention for emerging memory applications 1,2]. In the early stage, the conventional ferroelectric materials are perovskites with the crystal structure of ABO3, such as PbZrxTi1–xO3 and BaTiO3 [3], [4], [5]. Although perovskite materials exhibit superior ferroelectric properties, these material still encounter some challenges for production due to the issues of etching difficulty and process compatibility with complementary-metal-oxide-semiconductor (CMOS) in addition to the limitation of thickness scalability [6]. Recently, industry standard gate dielectric material of HfO2-based thin films with ferroelectricity renew the interest in logic and memory applications. Many studies have shown that Si [7,8], Y [9], Al [10], and Zr [11] doped HfO2 thin films can trigger the ferroelectricity properties due to the formation of a non-centrosymmetric orthorhombic phase Pca21 [12], [13], [14]. Even un-doped HfO2 can induce ferroelectricity and negative capacitance (NC) effect with proper ferroelectric thickness, interface treatment, and gate stress engineering [15]. A mechanical stress imposed by the capping metal followed by the rapid thermal annealing was also responsible for stabilize and/or promote ferroelectric Pca21 phase in HfO2-based thin film [16], [17], [18], [19], [20].
Among the doped HfO2 ferroelectric thin films, only Zr doping concentration can reach large portion up to 50%, which is benefit for process control when facing thickness scaling. The hafnium zirconium oxide (HfZrO) with 50% Zr exhibits the excellent ferroelectric polarization characteristics owing to the formation of favorably ferroelectric orthorhombic phase through an appropriate Zr doping [21]. However, high diffusion coefficient of Zr atom at high post-metal deposition annealing (PMA) temperature may result in poor interface near Si [22] and degrade the ferroelectric switching characteristic. Therefore, in this work, we investigated the electric performance of the doped-HfZrO and stacked-HfZrO capacitors to evaluate the effect of deposition sequence and PMA process on ferroelectric polarization characteristics.
Section snippets
Experimental
A 10-nm-thick 50% zirconium doped hafnium oxide (HfZrO), namely doped-HfZrO, and 5-nm/5-nm-thick zirconium oxide/hafnium oxide (ZrO2/HfO2) film stacks, namely stacked-HfZrO thin films were chosen to clarify the impact of Zr deposition sequence. The metal-ferroelectric-N+ Si capacitors with doped HfZrO and stacked HfZrO were utilized to investigate the ferroelectric properties. Here, the highly doped N+ Si was used as bottom electrode. The process of ferroelectric capacitor device is briefly
Results and discussion
Fig. 2(a) shows the I–V curves of doped-HfZrO and stacked-HfZrO capacitors. We can observe the change of leakage current under various PMA temperatures. The leakage current measured at 2 V significantly increases from 4.3 nA to 115 nA with the increased PMA temperature up to 800 °C. The apparent increase on leakage current is due to the defect generation in HfZrO bulk or near interface of HfZrO and buffer SiO2 [22]. Since the mechanism of defect dynamics is highly correlated with ferroelectric
Conclusions
From our experimental results, we revealed that the ferroelectric capacitor devices using stacked HfZrO film shows the relatively low leakage current and good thermal stability in comparison with doped-HfZrO device at PMA of 600–800 °C. This is because the leakage paths caused by ZrO2 diffusion near the Si interface can be effectively suppressed by HfO2 bottom layer within stacked HfZrO, but may not be easily controlled in doped-HfZrO film due to the much higher diffusion coefficient of Zr atom
Credit author statement
Tsung-Ming Lee, Chien-Liang Lin, Chien-Liang Lin, Yu-Chi Fan, Sheng Lee, Hsiu-Ming Liu, Zi-You Huang, Shih-An Wang: Device Fabrication and Measurement, Wei-Dong Liu, Zhi-Wei Zheng, Chun-Hu Cheng: Electrical Characteristics Simulation. Hsiao-Hsuan Hsu: Conceptualization, Methodology, Writing- Reviewing and Editing
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Financial supports from the Ministry of Science and Technology of Taiwan (107-2221-E-027-060 -MY2) are greatly appreciated.
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