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. 2021 Nov 24;12(12):1436.
doi: 10.3390/mi12121436.

Optimization of the In Situ Biasing FIB Sample Preparation for Hafnia-Based Ferroelectric Capacitor

Qilan Zhong  1 , Yiwei Wang  1 , Yan Cheng  1 , Zhaomeng Gao  2   3 , Yunzhe Zheng  1 , Tianjiao Xin  1 , Yonghui Zheng  1 , Rong Huang  1 , Hangbing Lyu  2   3
Affiliations

Optimization of the In Situ Biasing FIB Sample Preparation for Hafnia-Based Ferroelectric Capacitor

Qilan Zhong et al. Micromachines (Basel). .

Abstract

Hafnia-based ferroelectric (FE) thin films have received extensive attention in both academia and industry, benefitting from their outstanding scalability and excellent CMOS compatibility. Hafnia-based FE capacitors in particular have the potential to be used in dynamic random-access memory (DRAM) applications. Obtaining fine structure characterization at ultra-high spatial resolution is helpful for device performance optimization. Hence, sample preparation by the focused ion beam (FIB) system is an essential step, especially for in situ biasing experiments in a transmission electron microscope (TEM). In this work, we put forward three tips to improve the success rate of in situ biasing experiments: depositing a carbon protective layer to position the interface, welding the sample on the top of the Cu column of the TEM grid, and cutting the sample into a comb-like shape. By these means, in situ biasing of the FE capacitor was realized in TEM, and electric-field-induced tetragonal (t-) to monoclinic (m-) structure transitions in Hf0.5Zr0.5O2 FE film were observed. The improvement of FIB sample preparation technology can greatly enhance the quality of in situ biasing TEM samples, improve the success rate, and extend from capacitor sample preparation to other types.

Keywords: FIB sample preparation technology; hafnia-based ferroelectric; in situ biasing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Focused ion beam (FIB) sample preparation step diagram. (a) Full top view of the capacitors with different size of the electrodes. (b) Deposited carbon as protective layer. (c) Deposited tungsten as protective layer. (d) Dig holes on both sides. (e) U-cut. (f) Weld easy lift to capacitor slice. (g) Lift out capacitor slice. (h) Weld capacitor slice on the Cu grid. (i) Cut the connection. (j) Cut under high current condition. (k) Cut under low current condition. (l) Cut into three comb-like capacitor slices.
Figure 2
Figure 2
Comparison of different protective layers in thinning. (a) The sample is first covered with a protective carbon layer. (b) Magnified partial sample of a. (c) The sample is covered with the protective tungsten layers. (d) Magnified partial sample of (c).
Figure 3
Figure 3
Advantages of welding the sample to the top of the column. (a) Simulation of polishing sample in Precision Ion Polishing System (PIPS). (b) Magnified column section of Cu grid. (c) The case that sample welded at the top of the column. (d) The case that sample welded at the side of the column.
Figure 4
Figure 4
Final view of the comb-like capacitors for in situ electrical and structural characterization in transmission electron microscopy (TEM).
Figure 5
Figure 5
The Hf0.5Zr0.5O2 (HZO) thin film for in situ electrical experiments. (a) Schematic diagram of the HZO-based ferroelectric thin film capacitance structure for experiment. (b) Typical P–V curves of HZO(5nm) capacitor. (c) The tendency of Pr to cycles under 2.5 V. (d) High resolution TEM (HRTEM) image shows the in situ biasing process for a local area in the HZO thin film with the aid of tungsten probe.
Figure 6
Figure 6
Atomic structure changes in phase transition region before and after electrification. (a) High magnification capacitor structure before electrification. (b) Enlarged high-angle annular dark-field (HAADF) and annular bright-field (ABF) diagrams of t-phases. (c) Atomic model of tetragonal phase. (d) High magnification capacitor structure after electrification. (e) Enlarged HAADF and ABF diagrams of m-phases monoclinic phase. (f) Atomic model of monoclinic phase.
Figure 7
Figure 7
Regions where the phase structure did not change during electrification. (a) Low magnification image of grain that did not undergo phase transformation. (b) Atomic model of monoclinic phase. (c) Enlarged HAADF and ABF diagrams of m-phases.
See this image and copyright information in PMC

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