Investigation of charge loss characteristics of HfO2 annealed in N2 or O2 ambient

Yuqiong Chu; Zongliang Huo; Yulong Han; Guoxing Chen; Dong Zhang; Xinkai Li; Ming Liu

doi:10.1088/1674-4926/35/8/083004

J. Semicond. > 2014, Volume 35 > Issue 8 > 083004

SEMICONDUCTOR MATERIALS

Investigation of charge loss characteristics of HfO₂ annealed in N₂ or O₂ ambient

Yuqiong Chu, Zongliang Huo, Yulong Han, Guoxing Chen, Dong Zhang, Xinkai Li and Ming Liu

+ Author Affiliations

Corresponding author: Huo Zongliang, Email:huozongliang@ime.ac.cn; Liu Ming, Email:liuming@ime.ac.cn

DOI: 10.1088/1674-4926/35/8/083004

Abstract: The retention characteristics of electrons and holes in hafnium oxide with post-deposition annealing in a N₂ or O₂ ambient were investigated by Kelvin probe force microscopy. The KFM results show that compared with the N₂ PDA process, the O₂ PDA process can lead to a significant retention improvement. Vertical charge leakage and lateral charge spreading both played an important role in the charge loss mechanisms. The retention improvement is attributed to the deeper trap energy. For electrons, the trap energy of the HOS structure annealed in a N₂ or O₂ ambient were determined to be about 0.44 and 0.49 eV, respectively. For holes, these are about 0.34 and 0.36 eV, respectively. Finally, the electrical characteristics of the memory devices are demonstrated from the experiment, which agreed with our characterization results. The qualitative and quantitative determination of the charge retention properties, the possible charge decay mechanism and trap energy reported in this work can be very useful for the characterization of hafnium charge storage devices.

Key words: KFM, HfO₂, retention

1. Introduction

A charge trap flash (CTF) memory is widely accepted as a candidate for the next generation nonvolatile memory devices due to its significant advantages such as localized charge storage and coupling-free structure^{[1, 2]}, which are particularly important for 3D applications. To achieve a large memory window under low program/erase (P/E) voltages on CTF memory devices, the typical silicon nitride trapping layer can be replaced by high- $k$ materials such as HfO $_{2}$ with small equivalent nitride thickness^[3-7]. Although some work has been done for HfO $_{2}$ material optimization^[8], investigation of its reliability characteristics, such as the poor retention property, is still an important issue and becomes more important for future high-density applications. To improve the retention characteristics, it is founded that the post-deposition annealing (PDA) process is essential for the properties of HfO $_{2}$ ^[9]. However, the detailed retention degradation mechanism of HfO $_{2}$ annealed in a different ambient has not yet been investigated^[10]. To further understand the properties of the retention degradation mechanism as a guide for device performance optimization in CTF, it is of great importance to directly investigate the vertical and lateral charge loss characteristics for HfO $_{2}$ annealed in a different ambient, and the properties of trap energy. However, conventional charge pumping and 1/ $f$ noise technology mainly focus on the Si/SiO $_{2}$ interface properties, and cannot investigate the properties of the HfO $_{2}$ trapping layer directly^{[11, 12]}. Kelvin probe force microscopy (KFM) is a very powerful tool in investigating the retention characteristics by measuring contact potential difference (CPD) line profiles and calculating the charge density after charge injection^[13]. Although the trapping properties and retention characteristics of electrons have been determined in some studies^[9], only a limited number of reports have discussed the hole trapping properties in the HfO $_{2}$ trapping layer. Furthermore, the trapping properties, retention characteristics, and trap energy have never been simultaneously determined on one set of samples using the same measurement method. Since variations in growth conditions, dielectric stack structures, and measurement techniques can result in a large variation of extracted charge trapping properties, a systematical study of all these trapping properties for both electrons and holes on one specific sample set using the same experimental method is highly desirable. In this work, we employ the technique of variable temperature KFM to study the trapping properties, retention characteristics, and trap energy (of both electrons and holes), in HfO $_{2}$ annealed in a different ambient.

2. Experiment setup

The structure of HfO $_{2}$ -oxide-silicon was fabricated on an 8-12 $\Omega \cdot$ cm p-type Si (100) substrate. After standard cleaning, a 4-nm SiO $_{2}$ layer was thermally grown at 900 ℃ in dry O $_{2}$ ambient. Then, a 10 nm HfO $_{2}$ layer was subsequently deposited by atomic layer deposition at 150 ℃. Finally, all devices were treated by post-deposition annealing for 60 s in a N $_{2}$ or O $_{2}$ ambient at 1000 ℃. Data retention behavior was visualized by KFM technology, with Bruker's newest scanning probe microscopy system (Multimode 8). All samples before measurement had been prebaked at 105 ℃ for more than 120 min to desorb humidity.

Charge injection was done by scans (speed of 0.6 Hz and vertical electric field of 12 MV/cm) when the probe was under contact mode, where a 0.6-Hz scan speed guarantees injected charge saturation, as illustrated in Fig. 1(a). In the KFM mode, the cantilever measures and records the surface topography. Then, 2-D potential images of injected charges were visualized in the interleave scan of the KFM mode along the recorded topography, as illustrated in Fig. 1(b).

Figure 1. Schematic sample structure and KFM analysis method (a) charge injection with contact mode and (b) contact potential differences (CPDs) measurement.

DownLoad: Full-Size Img PowerPoint

For MAHOS devices, based on the fabrication of the HfO $_{2}$ -oxide-silicon structure, a 15 nm Al $_{2}$ O $_{3}$ was deposited on the HOS by ALD at 200 ℃ as a blocking layer, followed by post-deposition annealing for 60 s in a N $_{2}$ or O $_{2}$ ambient. Finally, 200 nm Al gate was deposited by an e-beam evaporator as a gate electrode to complete the MAHOS structure. The electrical measurements were performed by an Agilent B1500 semiconductor characterization system.

3. Results and discussion

Based on the $C$ - $V$ measurements, the dielectric constants of the HfO $_{2}$ samples are firstly extracted, of which there were 20. KFM tests were performed to explore the data retention characteristics and HfO $_{2}$ samples annealed in different ambients. shows the measured contact potential difference (CPD) line profiles of a sample with a HfO $_{2}$ trapping layer after charge injection. The line profiles are obtained by extracting a horizontal scan-line across the injection center in the 2-D potential image. The inset regions denote the trapped electrons, which present the evolution of the surface potential image at different elapsed times. The downward arrow in describes that the CPD peak value decreases due to vertical decay and lateral spreading and the left arrow describes that the widening of CPD profiles only results from lateral spreading. We calculated the initial injected charge density from the CPD peak value, which is based on the assumption of two extreme charge distributions: charges are trapped in the trapping bulk (Ⅰ) or at the interface (Ⅱ)^[14]. The two assumptions of the charge distribution have the same trend in a charge density calculation. For simplicity, we use distribution (Ⅱ) as our calculation method. Meanwhile, compared to the N $_{2}$ PDA sample, a larger CPD peak value, larger charge injection and less decay are observed for the O $_{2}$ PDA sample in Fig. 2(c).

Figure 2. The measured CPDs profiles after injection of electrons and holes of samples annealed in (a) N

$_{2}$ and (b) O

$_{2}$ ambient (c) injected electron and hole density in 0 s and after 7560 s.

DownLoad: Full-Size Img PowerPoint

Under the same estimating strategy, charge retention characteristics are extracted from different samples with a normalized electron and hole density as shown in . The overall charge decay of the N $_{2}$ -PDA HfO $_{2}$ trapping layer is larger than O $_{2}$ -PDA ones. The overall charge decay of holes is larger than the electrons.

Figure 3. Normalized electron and hole densities (

$\sigma _{\rm T}$ /

$\sigma _{\rm T 0})$ evolution versus the elapsed time corresponding to samples annealed in a N

$_{2}$ and O

$_{2}$ ambient, which present the overall performance of retention. }

DownLoad: Full-Size Img PowerPoint

Considering that the retention property has a strong relation with the vertical decay and lateral diffusion as illustrated in , we integrate charge densities from the extracted CPDs to obtain the remaining proportion after 7560 s, which remain at 0.9216, 0.8889, 0.7948, and 0.7491, corresponding to the electron density of the samples annealed in an O $_{2}$ or N $_{2}$ ambient, and the hole density of the samples annealed in an O $_{2}$ or N $_{2}$ ambient, respectively. We can conclude that the O $_{2}$ PDA condition is effective in reducing the total charge loss.

To further understand the charge loss characteristics in HfO $_{2}$ , the lateral charge spreading is another concern to be evaluated. As illustrated in Fig. 4, the electron density profile can be fitted by a Gaussian distribution. Selected potential line profiles are fitted by the following equation to qualify the diffusion coefficient^[15].

$\begin{equation} p=\frac{U}{2\sqrt{\pi D_{\rm p}(t+t_0)}}\exp\left[-\frac{x^2}{4D_{\rm p}(t+t_0)} \right], \end{equation}$

(1)

Figure 4. Charge density line profiles (dot lines) and their fitted curve using Eq. (1) (thin lines) of devices annealed in N

$_{2}$ ambient.

DownLoad: Full-Size Img PowerPoint

where $p$ , $U$ , $D_{\rm p}$ , $t$ and $x$ are the charge density, the constant related to the initial charge density, the diffusion coefficient, elapsed time, and lateral dimension, respectively. The fitting results are illustrated in Table 1.

Table 1. Extracted diffusion coefficients for different samples.

DownLoad: CSV | Show Table

The results show that the lateral diffusion of HfO $_{2}$ material annealed in O $_{2}$ ambient is smaller than the N $_{2}$ -PDA ones. The lateral diffusion coefficient of holes is larger than electrons as well. The lateral charge spreading characteristics evaluated by the diffusion coefficient are in good agreement with the aforementioned total charge loss properties.

To determine the effective trap energies of charges trapped in the HfO $_{2}$ trapping layer, we studied their retention behavior at elevated temperatures. We assume that the thermal emission, which is the thermal excitation of trapped electrons (holes) from the trap centers in HfO $_{2}$ to the conduction (valence) band, followed by the oxide tunneling process, is the main decay process.

Firstly, using the calculated charge trap density in each sample, we can obtain the retention times $\tau$ at different temperatures, then trap energy $E_{\rm t}$ can also be determined from the linear relationship between log( $\tau T^{2})$ and $1/T$ .

$\begin{equation} \log (\tau T^2)=-\log(ae_{\rm bb})+\frac{E_{\rm t}}{2.3k_{\rm B}}\frac{1}{T}. \end{equation}$

(2)

shows the CPD decay profiles of the sample with a N $_{2}$ -PDA HfO $_{2}$ trapping layer at 25 ℃; the 90 ℃ results show that CPD decay becomes more severe at high temperatures. shows the retention behavior at high temperatures, and we extracted the effective retention time $\tau$ from the slope, which is closely related to the thermal emission and band-to-band tunneling. Using $\tau$ values at different $T$ , we obtain the effective trap energies by linear fitting as illustrated in Fig. 5(c) when we employ the Shockley-Read-Hall (SRH) model. The results are illustrated in Table 2.

Table 2. Extracted trap energy levels for different samples. Unit: eV

DownLoad: CSV | Show Table

Considering all the above, it is concluded that, compared to N $_{2}$ -PDA, the O $_{2}$ -PDA HfO $_{2}$ trapping layer shows the better retention characteristics in both the vertical and lateral directions. Vertical charge leakage and lateral charge spreading both play important roles in the charge loss mechanisms. The retention improvement is attributed to the deeper effective trap energies.

Finally, memory devices annealed at different ambients are fabricated and measured^[16]. presents the high-frequency (100 kHz) $C$ - $V$ hysteresis of the two samples under $\pm$ 15 V sweep voltage to observe the memory effect. The results show that the device annealed in the O $_{2}$ ambient has a larger memory window. The memory effect of the MAHOS structure originates from the intrinsic HfO $_{2}$ traps and the trap sites at the interface. Larger memory windows indicate that the PDA processes have an impact on the trap density of the AHOS structure, which agrees with the KFM result in Fig. 2(c).

Figure 5. (a) CPD decay profiles of the sample with HfO

$_{2}$ trapping layer at 90 ℃ and 25 ℃. (b) ln(

$\sigma _{\rm I})$ -

$t$ plots, which are converted from CPD peak values by assuming charges are distributed at the interface, where

$E_{\rm T}$ is the effective trap energy. (c) Relationship between

$\tau T^{2}$ (unit: sK

$^{2})$ and

$1/T$ (unit: K

$^{-1})$ , where

$\alpha$ is the combination of temperature independent constants, and

$e_{\rm bb}$ is the direct tunneling of electrons through the oxide from HfO

$_{2}$ conduction band into the silicon conduction band.

DownLoad: Full-Size Img PowerPoint

Data retention properties with an identical initial flat-band voltage are shown in . We can see that the retention characteristics of the O $_{2}$ PDA device at 25 ℃, 85 ℃ is better than the device annealed in the N $_{2}$ ambient. Comparing these results with Fig. 3, the results are in good agreement.

Figure 6. The high-frequency (100 kHz)

$C$ -

$V$ hysteresis of the two samples under

$\pm$ 15 V sweep voltage.

DownLoad: Full-Size Img PowerPoint

With Al $_{2}$ O $_{3}$ as the blocking oxide layer, the gate leakage current properties at 25 ℃ and 85 ℃ of samples annealed in N $_{2}$ and O $_{2}$ ambients are shown in . It is shown that the gate leakage current of the O $_{2}$ PDA device is smaller than the device annealed in the N $_{2}$ ambient at 25 ℃, 85 ℃. Comparing these results with , we can know that the post-deposition anneal in the O $_{2}$ ambient improved the retention characteristics in MAHOS memory devices by reducing the leakage current and then improving the retention characteristics.

Figure 7. Data retention properties at 25 ℃ and 85 ℃ with an identical initial

$V_{\rm fb}$ of samples annealed in N

$_{2}$ and O

$_{2}$ ambients.

DownLoad: Full-Size Img PowerPoint

Figure 8. Gate leakage current properties at data retention properties at 25 ℃ and 85 ℃ of samples annealed in N₂ and O₂ ambients.

DownLoad: Full-Size Img PowerPoint

4. Conclusion

In summary, the HfO $_{2}$ material annealed in O $_{2}$ -PDA shows a larger injected charge density, and a better retention characteristic in both the vertical and lateral directions than N $_{2}$ -PDA ones. Vertical charge leakage and lateral charge spreading both play important roles in the charge loss mechanisms. The retention improvement is attributed to the deeper effective trap energies. Finally, the electrical characteristics of memory devices are demonstrated from the experiment, which agreed with our characterization results.

References

[1]	Kim K. From the future Si technology perspective:challenges and opportunities. Electron Devices Meeting, 2010, 1(1):1 http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5703274
[2]	Wang Y Q, Hwang W S, Zhang G, et al. Electrical characteristics of memory devices with a high-k HfO₂ trapping layer and dual SiO₂/Si₃N₄ tunneling layer. IEEE Trans Electron Devices, 2007, 54(10):2700 http://ieeexplore.ieee.org/document/4317755/
[3]	You H W, Cho W J. Charge trapping properties of the HfO₂ layer with various thicknesses for charge trap flash memory applications. Appl Phys Lett, 2010, 96(9):093506 doi: 10.1063/1.3337103
[4]	Yuan C L, Chan M Y, Lee P S, et al. Al₂O₃ nanocrystals embedded in amorphous Lu₂O₃ high-k gate dielectric for floating gate memory application. J Phys:Conference Series, 2007, 61(1):1312 http://adsabs.harvard.edu/abs/2007JPhCS..61.1312Y
[5]	Ding S J, Zhang D W, Wang L K. Atomic-layer-deposited Al₂O₃-HfO₂ laminated and sandwiched dielectrics for metal-insulator-metal capacitors. J Phys D:Appl Phys, 2007, 40(4):1072 doi: 10.1088/0022-3727/40/4/023
[6]	Maikap S, Rahaman S Z, Tien T C, et al. Nanoscale (EOT = 5.6 nm) nonvolatile memory characteristics using n-Si/SiO₂/HfAlO nanocrystal/Al₂O₃/Pt capacitors. Nanotechnology, 2008, 19(43):435202 doi: 10.1088/0957-4484/19/43/435202
[7]	Sugizaki T, Kohayashi M, Ishidao M, et al. Novel multi-bit SONOS type flash memory using a high-k charge trapping layer. Symposium on VLSI Technology, 2003:27 http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=1221069
[8]	Spiga S, Driussi F, Lamperti A. Experimental and simulation study of the program efficiency of HfO₂ based charge trapping memories. Solid-State Device Research Conference (ESSDERC), 2010:408 http://ieeexplore.ieee.org/abstract/document/5618194/
[9]	Zhu Chenxin, Yang Rong, Huo Zongliang, et al. Investigation of charge trap and loss characteristics for charge trap memory by electrostatic force microscopy. Non-Volatile Memory Technology Symposium (NVMTS), 2011:1 http://ieeexplore.ieee.org/document/6137099/
[10]	Chowdhury N A, Garg R, Misra D, et al. Charge trapping and interface characteristics of thermally evaporated HfO₂. Appl Phys Lett, 2004, 85(15):3290 doi: 10.1063/1.1805708
[11]	Ryan J T, Yu L C, Han J H, et al. A new interface defect spectroscopy method. IRPS, 2011:203 http://ieeexplore.ieee.org/document/5872242/
[12]	Uren M J. The properties of individual Si/SiO₂ defects and their link to 1/f noise. Mater Sci Forum, 1992, 83-87:1519 doi: 10.4028/www.scientific.net/MSF.83-87
[13]	Girard P. Electrostatic force microscopy:principles and some applications to semiconductors. Nanotechnology, 2001, 12(4):485 doi: 10.1088/0957-4484/12/4/321
[14]	Tzeng S D, Gwo S. Charge trapping properties at silicon nitride/silicon oxide interface studied by variable-temperature electrostatic force microscopy. J Appl Phys, 2006, 100(2):023711 doi: 10.1063/1.2218025
[15]	Baik S J, Lim K S. Lateral redistribution of trapped charges in nitride/oxide/Si (NOS) investigated by electrostatic force microscopy. Nanoscale, 2011, 3:2560 doi: 10.1039/c1nr10104h
[16]	Chen Yong, Zhao Jianming, Han Dedong, et al. Extraction of equivalent oxide thickness for HfO₂ high k gate dielectrics. Chinese Journal of Semiconductors, 2006, 27(5):852

Fig. 1. Schematic sample structure and KFM analysis method (a) charge injection with contact mode and (b) contact potential differences (CPDs) measurement.

DownLoad: Full-Size Img PowerPoint

Fig. 2. The measured CPDs profiles after injection of electrons and holes of samples annealed in (a) N

$_{2}$ and (b) O

$_{2}$ ambient (c) injected electron and hole density in 0 s and after 7560 s.

DownLoad: Full-Size Img PowerPoint

Fig. 3. Normalized electron and hole densities (

$\sigma _{\rm T}$ /

$\sigma _{\rm T 0})$ evolution versus the elapsed time corresponding to samples annealed in a N

$_{2}$ and O

$_{2}$ ambient, which present the overall performance of retention. }

DownLoad: Full-Size Img PowerPoint

Fig. 4. Charge density line profiles (dot lines) and their fitted curve using Eq. (1) (thin lines) of devices annealed in N

$_{2}$ ambient.

DownLoad: Full-Size Img PowerPoint

Fig. 5. (a) CPD decay profiles of the sample with HfO

$_{2}$ trapping layer at 90 ℃ and 25 ℃. (b) ln(

$\sigma _{\rm I})$ -

$t$ plots, which are converted from CPD peak values by assuming charges are distributed at the interface, where

$E_{\rm T}$ is the effective trap energy. (c) Relationship between

$\tau T^{2}$ (unit: sK

$^{2})$ and

$1/T$ (unit: K

$^{-1})$ , where

$\alpha$ is the combination of temperature independent constants, and

$e_{\rm bb}$ is the direct tunneling of electrons through the oxide from HfO

$_{2}$ conduction band into the silicon conduction band.

DownLoad: Full-Size Img PowerPoint

Fig. 6. The high-frequency (100 kHz)

$C$ -

$V$ hysteresis of the two samples under

$\pm$ 15 V sweep voltage.

DownLoad: Full-Size Img PowerPoint

Fig. 7. Data retention properties at 25 ℃ and 85 ℃ with an identical initial

$V_{\rm fb}$ of samples annealed in N

$_{2}$ and O

$_{2}$ ambients.

DownLoad: Full-Size Img PowerPoint

Fig. 8. Gate leakage current properties at data retention properties at 25 ℃ and 85 ℃ of samples annealed in N₂ and O₂ ambients.

DownLoad: Full-Size Img PowerPoint

Table 1. Extracted diffusion coefficients for different samples.

Table 2. Extracted trap energy levels for different samples. Unit: eV

[1]	Kim K. From the future Si technology perspective:challenges and opportunities. Electron Devices Meeting, 2010, 1(1):1 http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=5703274
[2]	Wang Y Q, Hwang W S, Zhang G, et al. Electrical characteristics of memory devices with a high-k HfO₂ trapping layer and dual SiO₂/Si₃N₄ tunneling layer. IEEE Trans Electron Devices, 2007, 54(10):2700 http://ieeexplore.ieee.org/document/4317755/
[3]	You H W, Cho W J. Charge trapping properties of the HfO₂ layer with various thicknesses for charge trap flash memory applications. Appl Phys Lett, 2010, 96(9):093506 doi: 10.1063/1.3337103
[4]	Yuan C L, Chan M Y, Lee P S, et al. Al₂O₃ nanocrystals embedded in amorphous Lu₂O₃ high-k gate dielectric for floating gate memory application. J Phys:Conference Series, 2007, 61(1):1312 http://adsabs.harvard.edu/abs/2007JPhCS..61.1312Y
[5]	Ding S J, Zhang D W, Wang L K. Atomic-layer-deposited Al₂O₃-HfO₂ laminated and sandwiched dielectrics for metal-insulator-metal capacitors. J Phys D:Appl Phys, 2007, 40(4):1072 doi: 10.1088/0022-3727/40/4/023
[6]	Maikap S, Rahaman S Z, Tien T C, et al. Nanoscale (EOT = 5.6 nm) nonvolatile memory characteristics using n-Si/SiO₂/HfAlO nanocrystal/Al₂O₃/Pt capacitors. Nanotechnology, 2008, 19(43):435202 doi: 10.1088/0957-4484/19/43/435202
[7]	Sugizaki T, Kohayashi M, Ishidao M, et al. Novel multi-bit SONOS type flash memory using a high-k charge trapping layer. Symposium on VLSI Technology, 2003:27 http://ieeexplore.ieee.org/xpls/icp.jsp?arnumber=1221069
[8]	Spiga S, Driussi F, Lamperti A. Experimental and simulation study of the program efficiency of HfO₂ based charge trapping memories. Solid-State Device Research Conference (ESSDERC), 2010:408 http://ieeexplore.ieee.org/abstract/document/5618194/
[9]	Zhu Chenxin, Yang Rong, Huo Zongliang, et al. Investigation of charge trap and loss characteristics for charge trap memory by electrostatic force microscopy. Non-Volatile Memory Technology Symposium (NVMTS), 2011:1 http://ieeexplore.ieee.org/document/6137099/
[10]	Chowdhury N A, Garg R, Misra D, et al. Charge trapping and interface characteristics of thermally evaporated HfO₂. Appl Phys Lett, 2004, 85(15):3290 doi: 10.1063/1.1805708
[11]	Ryan J T, Yu L C, Han J H, et al. A new interface defect spectroscopy method. IRPS, 2011:203 http://ieeexplore.ieee.org/document/5872242/
[12]	Uren M J. The properties of individual Si/SiO₂ defects and their link to 1/f noise. Mater Sci Forum, 1992, 83-87:1519 doi: 10.4028/www.scientific.net/MSF.83-87
[13]	Girard P. Electrostatic force microscopy:principles and some applications to semiconductors. Nanotechnology, 2001, 12(4):485 doi: 10.1088/0957-4484/12/4/321
[14]	Tzeng S D, Gwo S. Charge trapping properties at silicon nitride/silicon oxide interface studied by variable-temperature electrostatic force microscopy. J Appl Phys, 2006, 100(2):023711 doi: 10.1063/1.2218025
[15]	Baik S J, Lim K S. Lateral redistribution of trapped charges in nitride/oxide/Si (NOS) investigated by electrostatic force microscopy. Nanoscale, 2011, 3:2560 doi: 10.1039/c1nr10104h
[16]	Chen Yong, Zhao Jianming, Han Dedong, et al. Extraction of equivalent oxide thickness for HfO₂ high k gate dielectrics. Chinese Journal of Semiconductors, 2006, 27(5):852

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Yuqiong Chu, Zongliang Huo, Yulong Han, Guoxing Chen, Dong Zhang, Xinkai Li, Ming Liu. Investigation of charge loss characteristics of HfO₂ annealed in N₂ or O₂ ambient[J]. Journal of Semiconductors, 2014, 35(8): 083004. doi: 10.1088/1674-4926/35/8/083004

Y Q Chu, Z L Huo, Y L Han, G X Chen, D Zhang, X K Li, M Liu. Investigation of charge loss characteristics of HfO2 annealed in N2 or O2 ambient[J]. J. Semicond., 2014, 35(8): 083004. doi: 10.1088/1674-4926/35/8/083004.

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Received: 10 January 2014 Revised: 10 March 2014 Online: Published: 01 August 2014

Article Navigation > Journal of Semiconductors > 2014 > 35(8): 083004

Yuqiong Chu, Zongliang Huo, Yulong Han, Guoxing Chen, Dong Zhang, Xinkai Li, Ming Liu. Investigation of charge loss characteristics of HfO2 annealed in N2 or O2 ambient[J]. Journal of Semiconductors, 2014, 35(8): 083004. doi: 10.1088/1674-4926/35/8/083004 ****Y Q Chu, Z L Huo, Y L Han, G X Chen, D Zhang, X K Li, M Liu. Investigation of charge loss characteristics of HfO2 annealed in N2 or O2 ambient[J]. J. Semicond., 2014, 35(8): 083004. doi: 10.1088/1674-4926/35/8/083004.

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Investigation of charge loss characteristics of HfO₂ annealed in N₂ or O₂ ambient

DOI: 10.1088/1674-4926/35/8/083004

Laboratory of Nano-Fabrication and Novel Devices Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China

Funds:

the National Natural Science Foundation of China 61176073

the MOST 2011CBA00600

the MOST 2010CB934200

Project supported by the MOST (Nos. 2010CB934200, 2011CBA00600) and the National Natural Science Foundation of China (No.61176073)

More Information

Corresponding author: Huo Zongliang, Email:huozongliang@ime.ac.cn; Liu Ming, Email:liuming@ime.ac.cn
Received Date: 2014-01-10
Revised Date: 2014-03-10
Published Date: 2014-08-01

Abstract

Abstract

The retention characteristics of electrons and holes in hafnium oxide with post-deposition annealing in a N₂ or O₂ ambient were investigated by Kelvin probe force microscopy. The KFM results show that compared with the N₂ PDA process, the O₂ PDA process can lead to a significant retention improvement. Vertical charge leakage and lateral charge spreading both played an important role in the charge loss mechanisms. The retention improvement is attributed to the deeper trap energy. For electrons, the trap energy of the HOS structure annealed in a N₂ or O₂ ambient were determined to be about 0.44 and 0.49 eV, respectively. For holes, these are about 0.34 and 0.36 eV, respectively. Finally, the electrical characteristics of the memory devices are demonstrated from the experiment, which agreed with our characterization results. The qualitative and quantitative determination of the charge retention properties, the possible charge decay mechanism and trap energy reported in this work can be very useful for the characterization of hafnium charge storage devices.
- KFM,
- HfO₂,
- retention

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