無摻雜氧化鉿鐵電電容器和電晶體元件電性可靠度研究

Electrical Reliability Investigative of Dopant-Free Hafnium Oxide Metal-Ferroelectric-Metal Capacitor and Field-Effect Transistor

黃子祐(Huang Zi-You)

指導教授 ： 鄭淳護

國立臺灣師範大學/科技與工程學院/機電工程學系/碩士(2020年)

https://doi.org/10.6345/NTNU202001112

摘要

隨著物聯網(Internet of Things)、車聯網(Internet of Vehicles)、人工智慧(Artificial Intelligence)及大數據(Big data)的蓬勃發展下，對於電子元件的需求與日俱增隨著元件不斷的微縮，在晶片單位面積上的元件數量隨之增加，總功率消耗有增加的趨勢，因此克服功率消耗成為重要的議題。藉由鐵電材料中的負電容效應，可以使傳統電晶體之次臨界擺幅(Subthreshold Swing, SS)低於60 mV/decade，因而進一步降低器件的功率消耗。傳統的鐵電材料像是鋯鈦酸鉛(lead zirconate titanate , PZT) 和鉭酸鍶鉍(strontium bismuth tantalite, SBT)等，有著難以微縮以及環境污染的問題。
且近年來發現二氧化鉿材料能透過摻雜和金屬閘極的機械應力誘發鐵電特性，因此引起研究者的關注。再加上科技的走向，電子元件逐漸朝向尺寸微縮、低功率消耗和高速等趨勢發展，其中以鐵電特性為架構的鐵電隨機存取記憶體及負電容場效電晶體漸漸受到重視，然而高濃度摻雜鋯會使得元件漏電流的增加，而摻雜鋁會使得元件微縮時摻雜比例不易調控，故無摻雜氧化鉿逐漸受到重視且具研究價值。
文獻中所示，無摻雜二氧化鉿薄膜可以透過厚度微縮及閘極應力誘發二氧化鉿材料結晶相轉變進而增強鐵電極化特性，本研究將10奈米的二氧化鉿薄膜微縮至7奈米，利用厚度效應來達到增強鐵電特性。厚度微縮雖然可以增強鐵電及化特性，但同時增加漏電流，為了改善漏電流的缺點本研究將二氧化鉿薄膜表面進行氮電漿處理。藉由氮電漿修補薄膜表面缺陷進而降低漏電流及改善元件可靠度，可靠度分析發現經過氮電漿修補後陷阱能障從0.453 eV改善至0.474 eV，將薄膜用於鐵電電晶體發現，經過氮電漿處理後臨界電壓從0.955 V偏移至1.65 V，缺陷視窗縮減0.25 V。此研究結果有助於將無摻雜二氧化鉿薄膜整合於記憶體。

關鍵字

無摻雜二氧化鉿 ； 厚度效應 ； 金屬應力 ； 氮電漿

並列摘要

With the rapid development of Internet of things, Internet of vehicles, artificial intelligence and big data, the demand for electronic components is increasing day by day. With the continuous miniaturization of components, the number of components per chip area increases, and the total power consumption tends to increase. Therefore, overcoming power consumption has become an important topic. Because of the negative capacitance effect within ferroelectric materials, the subthreshold swing (SS) of traditional transistors can be lowered than 60 mV / decade, which can reduce the power consumption of the devices. Traditional ferroelectric materials, such as lead zirconate titanate, PZT and strontium bismuth tantalite, SBT and so on, suffer the process problems on miniaturization and environmental pollution. Therefore, dopant-free HfO2 with ferroelectricity as ferroelectric material for ferro device fabrication, which can effectively overcome the issues of element miniaturization and environmental pollution.
In recent years, it has been found that HfO2 can induce ferroelectric properties through doping and the mechanical stress of metal gate, which has attracted the attention of researchers. In addition, with the development of science and technology, electronic components are gradually developing towards the trend of miniaturization, low power consumption and high speed. Among them, the low power technologies development of ferroelectric random access memory and “negative capacitance” logic transistor are widely investigated by Globe research groups. However, the common issues such as dopant diffusion (Zr), narrow doping tuning window, poor interface thermal stability, still need to be comprehensively studied.
It has been shown in the literature that undoped HfO2 thin films can enhance the ferroelectric polarization properties by thickness reduction and gate stress induced crystal phase transformation. In this study, the thickness scaling strategy was used to enhance the ferroelectric properties of HfO2 thin films by reducing the thickness from 10 nm to 7 nm. Although the thickness reduction can enhance the ferroelectric and property, it also increases the magnitude of leakage current. In order to improve the leakage current, the surface passivation of hafnium dioxide film was treated by nitrogen plasma. We can find that the trap energy barrier of dopant-free HfO2 was improved from 0.453 eV to 0.474 eV after nitrogen passivation. The threshold voltage was shifted from 0.955 V to 1.65 V and the trap window was reduced by 0.25 V. The experimental results demonstrate that the ferroelectricity of dopant-free HfO2 can be improved by both thickness scaling strategy and remote nitrogen plasmas passivation, which can be beneficial for the integration on ferroelectric memory and negative capacitance transistor technologies.

並列關鍵字

Dopant-free HfO2 ； Thickness effect ； Metal stress ； Nitrogen-plasma

參考文獻

[1]C. Ahn, K. Rabe, and J.-M. Triscone, "Ferroelectricity at the nanoscale: local polarization in oxide thin films and heterostructures," Science, vol. 303, no. 5657, pp. 488-491, 2004.

[2]S. Salahuddin and S. Datta, "Use of negative capacitance to provide voltage amplification for low power nanoscale devices," Nano letters, vol. 8, no. 2, pp. 405-410, 2008.

[3]K. Jang, T. Saraya, M. Kobayashi, and T. Hiramoto, "Ion/Ioff ratio enhancement and scalability of gate-all-around nanowire negative-capacitance FET with ferroelectric HfO2," Solid-State Electronics, vol. 136, pp. 60-67, 2017.

[4]C.-H. Cheng, C.-C. Fan, C.-Y. Tu, H.-H. Hsu, and C.-Y. Chang, "Implementation of dopant-free hafnium oxide negative capacitance field-effect transistor," IEEE Transactions on Electron Devices, vol. 66, no. 1, pp. 825-828, 2018.

[5]E. Yurchuk et al., "Impact of scaling on the performance of HfO2-based ferroelectric field effect transistors," Ieee Transactions on Electron Devices, vol. 61, no. 11, pp. 3699-3706, 2014.