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Article

Performance Improvement of Total Ionization Dose Radiation Sensor Devices Using Fluorine-Treated MOHOS

1
Minghsin University of Science and Technology, Xinfeng 30401, Taiwan
2
Treasure Giant Technology Inc., Hsinchu City 30068, Taiwan
3
Southern Taiwan University of Science and Technology, Tainan 71005, Taiwan
4
National Nano Device Laboratories, Hsinchu 30078, Taiwan
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Sensors 2016, 16(4), 450; https://doi.org/10.3390/s16040450
Submission received: 3 February 2016 / Revised: 18 March 2016 / Accepted: 23 March 2016 / Published: 29 March 2016

Abstract

:
Fluorine-treated titanium nitride–silicon oxide–hafnium oxide–silicon oxide–silicon devices (hereafter F-MOHOS) are candidates for total ionization dose (TID) radiation sensor applications. The main subject of the study reportedherein is the performance improvement in terms of TID radiation-induced charge generation effect and charge-retention reliability characterization for F-MOHOS devices. In the case of F-MOHOS TID radiation sensors, the gamma radiation induces a significant decrease of threshold voltage VT and the radiation-induced charge density is nearly six times larger than that of standard metal–oxide–nitride–oxide–silicon MONOS devices. The decrease of VT for F-MOHOS after gamma irradiation has a strong correlation to the TID up to 5 Mrad gamma irradiation as well. The improvement of charge retention loss for F-MOHOS devices is nearly 15% better than that of metal–oxide–hafnium oxide–oxide–silicon MOHOS devices. The F-MOHOS device described in this study demonstrates better feasibility for non-volatile TID radiation sensing in the future.
Keywords:
SONOS; NVM; sensor; gamma ray

1. Introduction

The total ionizing dose (TID) radiation-induced charging effect is a major application concern for the operation of electronic devices in advanced X-ray lithography semiconductor manufacturing processes and outer space applications. When a metal-silicon dioxide-silicon (MOS) structure is irradiated by gamma rays, positive charges build-up at the Si-SiO2 interface and an interface state occurrs in the structure [1]. The radiation-induced charging effects of a metal–nitride–oxide–silicon (MNOS) device with stacked insulation layers composed of silicon nitride and silicon dioxide have been reported [2]. The radiation-induced charging effects on traditional silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile memory (NVM) devices have also been studied before. [3,4]. Until now, little was known about the radiation response of SONOS–like devices with high k charge-trapping structure [4,5]. High-k gate dielectrics have been used for reducing transistor gate leakage current in advanced nano-scale CMOS device technology [5]. Recently, conventional SONOS flash memory was replaced with silicon–oxide–hafnium oxide–oxide–silicon SOHOS devices (hafnium-based SONOS-like devices with high k material as charge-trapping structure). However, SOHOS devices have worse data retention characteristics, as is well known [5]. The effects of radiation response on a few SOHOS-like devices have been reported [4,5], but the charge retention reliability of the SOHOS device as TID radiation sensor has not been well studied and it will be the main subject of this study. In order to improve the radiation-induced charge density and charge retention reliability of SOHOS device for non-volatile TID radiation sensor applications, a titanium nitride–silicon oxide–hafnium oxide–silicon oxide–silicon device with CF4 plasma treated hafnium oxide HfO2 (hereafter F-MOHOS) was fabricated. The electrical performance of F-MOHOS, including radiation-induced charge generation effect and charge retention reliability characterization, are the main subjects of discussion in this paper, which reports a study of different types of F-treated MOHOS to manipulate the radiation-induced charging effects and charge retention reliability characterization of F-treated HfO2. In contrast to the previous publication [4], the MOHOS devices were irradiated by gamma irradiation with negative gate bias stress (NVS). The NVS application increases the survival yield of radiation-induced electron-hole pairs from the initial recombination process and also increases the radiation-induced charging yield of the MOS type devices [6].

2. Experimental Section

The MOHOS devices prepared with various F-treated HfO2 materials are listed in Table 1. MOHOS structures were fabricated on p-type resistivity 15–25 Ω-cm Si <100> substrate. To fabricate MONOS devices, we used thermal silicon oxide SiO2 as tunneling oxide, CVD silicon nitride Si3N4 for the trapping layer, and CVD TEOS SiO2 as blocking oxide. The tunneling oxide (SiO2) was formed on the wafers by using an advanced clustered vertical furnace. After the tunneling oxide formation, silicon nitride (hereafter, nitride, Si3N4) was deposited as the charge-trapping layer by low-pressure chemical vapor deposition (LPCVD) for MONOS devices.
For MOHOS devices, HfO2 films (10~20 nm) were deposited as the charge-trapping layers, with Hf(tert-butoxy)2(mmp)2 precursor in a metal organic chemical vapor deposition (MOCVD) system at 400 ~ 550 °C. For F-MOHOS devices, CF4 plasma treatment with 30 sccm at 50 W for 30 s was performed on MOHOS. To manipulate the radiation-induced charging effects in F-treated HfO2, three type of F-treated MOHOS were prepared: (1) “FB” type MOHOS (hereafter FB-MOHOS), CF4 plasma treatment before HfO2 deposition; (2) “FA” type MOHOS (hereafter FA-MOHOS), CF4 plasma treatment after HfO2 deposition; (3) “FAB” type MOHOS (hereafter FAB-MOHOS), CF4 plasma treatment both before and after HfO2 deposition. The SiO2–Si3N4–SiO2 (hereafter ONO) gate stack consists of a 100 Å–200 Å silicon nitride and 50 Å–150 Å bottom and top silicon oxides. TiN metal gate (200–400 nm) was formed by DC sputtering for the control gate. After gate patterning, source and drain were formed by implantation with arsenic atoms which were activated at 900 °C for 30 s. Figure 1a shows a cross-section view of the MOHOS devices. For comparison, all the devices listed in Table 1 have the same tunneling oxide, charge-trapping layer and blocking oxide layer thickness. A MOHOS device with dimensions W x L = 0.1 × 0.1 mm2 was used in this paper.
For gamma TID data writing, in this study all the devices listed in Table 1 were exposed to 60Co gamma radiation with gate negative bias stress (NVS, VG = −4 V). For the gamma TID data read, VT shifting was measured at room temperature using a HP4156A parameter analyzer. The of ID − VG curve experimental results of the MOHOS device pre-irradiation and post-irradiation were compared by a computer-controlled HP4156A parameter analyzer at room temperature. Figure 1b shows the charge generation and trapping states of the gate dielectric in the FAB-MOHOS device after gamma irradiation.

3. Results and Discussion

3.1. Radiation-Induced Charging Effect of F-MOHOS after Gamma Irradiation

As illustrated in Figure 2a, the ID − VG curve of MOHOS was shifted to the left after 5 Mrad TID of gamma irradiation. This implies that gamma irradiation induces a decrease of VT for MOHOS. The amount of decrease of VT is about 2.9 V. It is considered that the change is due to an increase in the net positive trapped charges in the HfO2 charge-trapping layer after gamma irradiation. The negative VT shift result agrees with those of previous studies [3,4]. These radiation-induced shifts in the irradiated device are a combination of two effects; the first effect is a result from the loss of stored negative charge in the HfO2 trapping layer and the second effect is due to a build-up of positive charge resulted from asymmetric trapping of electrons and holes in the HfO2 trapping layer.
The |delta VT| of the MOHOS device increases as a function of gamma TID, as indicated in Figure 2b. It also shows a quasi-linear correlation of |delta VT | vs. gamma TID below 100 krad in log scale, but |delta VT| increases more sharply after gamma irradiation at levels up to 100 krad TID. This result is in agreement with those of previous studies [4].
The radiation-induced |delta VT| and charge density comparisons after 5 Mrad TID gamma irradiation for various F-MOHOS devices shown in Table 1 are illustrated in Figure 3a,b The trapped charge density can be calculated by the Terman method [5]. As shown in Figure 3a, the radiation-induced VT shift of MOHOS is more significant than that of MONOS, which results from more radiation-induced charges in the HfO2 trapping layer than in the Si3N4 charging layer. In addition, the F-MOHOS devices with various F treatments (FA-, FB- and FAB-MOHOS) all demonstrate higher degrees of VT shift and higher radiation-induced charge density than the MOHOS devices. These results are contributed by a higher radiation-induced charging effect on these F-MOHOS devices than that on MOHOS devices. Note that the radiation-induced charge density of the FAB-MOHOS device is six times larger than that of traditional MONOS devices. The FAB-MOHOS device with larger F-treatment volume in HfO2 has the higher radiation-induced charge density than the FA-MOHOS and FB-MOHOS devices after gamma irradiation.

3.2. VT Stability vs. Retention Time

In this section, the radiation-induced charges-retention reliability characteristics of the F-MOHOS devices are discussed and these are the important electrical properties that need to be verified for their potential application in TID radiation sensors in this study. The VT stability vs. time for MOHOS under VG = −4 V before gamma irradiation and after 5 Mrad gamma irradiation is illustrated in Figure 4a,b respectively.
It is noted that the decrease of the VT with time for the pre-irradiated MOHOS device is a result of stored negative-charge tunneling out from the HfO2 trapping layer. Note that the increase of the VT with time for the post-irradiated MOHOS device is a result of radiation-induced positive charges tunneling out from the HfO2 trapping layer.
Figure 5a shows the VT stability versus time with NVS (VG = −4 V) for various F-MOHOS devices shown in Table 1 before gamma irradiation. It is seen that the device with HfO2 as the charge-storage layer shows the worst charge retention reliability characteristics compared with Si3N4. The worse charge storage capacity in the MOHOS device may be attributed to tunneling leakage current induced by interface trap states [7]. As shown in Figure 5a, the F-MOHOS devices demonstrate better charge-retention reliability characteristics than MOHOS ones before gamma irradiation, which is because deep negative-charge traps in F treated trapping HfO2 lead to less negative-charge loss and a better negative charge-retention reliability characteristics for the pre-irradiated F-MOHOS than the pre-irradiated MOHOS [7]. However, the FB-MOHOS device has better charge-retention reliability characteristics than the FA-MOHOS devices before gamma irradiation. Because the probability of stored negative-charge tunneling out from bottom of trapping HfO2 to tunneling oxide is higher (compared to that from top of trapping HfO2 to blocking oxide) for the pre-irradiated F-MOHOS device under NVS. Therefore, the FB-MOHOS device with deeper negative-charge traps at the bottom of HfO2 shows better charge-retention reliability characteristic than the FA-MOHOS devices before gamma irradiation.
Figure 5b shows the VT stability vs. time under VG = −4 V for various F-MOHOS devices after 5 Mrad TID gamma irradiation. We note that the FA-MOHOS demonstrate worse charge-retention reliability characteristics than the FB-MOHOS after 5 Mrad gamma irradiation because the probability of radiation-induced positive charges tunnel-out from the top of trapping nitride to blocking oxide is higher (compared to that from bottom of trapping nitride to tunneling oxide) for the 5 Mrad gamma irradiated F-MOHOS device under NVS. Therefore, the FA-MOHOS device with more deep negative-charge traps at the top of HfO2 shows better charge-retention reliability characteristic than the FB-MOHOS devices after 5 Mrad gamma irradiation. Furthermore, the F treatment process during HfO2 deposition should be considered for the traded-off between pre-irradiated and post irradiated charge-retention reliability. Therefore, the FAB-MOHOS device with deeper negative-charge traps both at the top and bottom of HfO2 is suggested for improvement of charge retention reliability characteristic both before gamma irradiation and after 5 Mrad gamma irradiation.

4. Conclusions

As shown by the experimental data, F treatment during HfO2 deposition is a very effective process for enhancing the radiation-induced charging effect of MOHOS devices. It can be explained by the fact that the enhanced radiation-induced charging effect of F-MOHOS was induced by more radiation-induced positive charges in the F-treated HfO2 trapping layer. In addition, the F treatment process during HfO2 deposition should be considered for the trade-off between pre-irradiated and post-irradiated charge-retention reliability. Therefore, the FAB-MOHOS device is suggested for improvement of charge retention reliability characteristics both before gamma irradiation and after 5 Mrad gamma irradiation. The results show that F-MOHOS devices with F-treated HfO2 charge-trapping layers can be potential candidate nonvolatile TID radiation sensors in the future.

Acknowledgments

The authors would also like to thank National Nano Device Laboratories (NDL), National Tsing Hua University (NTHU), and National Chiao Tung University (NCTU) to provide the instruments for wafer fabrication and testing. This paper was funded in part by the National Science Council (NSC) sponsor.

Author Contributions

The presented work is a product of the whole team. Wen-Ching Hsieh initiated the research idea and performed all the experiments. Weh-Ching Hiseh, Hao-Tien Daniel Lee, Fuh-Cheng Jong and Shich-Chuan Wu worked together to drafted the manuscripts for review.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. McWhorter, P.J.; Miller, S.L.; Dellin, T.A. Radiation response of SNOS nonvolatile transistors. IEEE Trans. Nucl. Sci. 1986, NS-33, 1414–1419. [Google Scholar] [CrossRef]
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  3. Qiao, F.Y.; Yu, X.; Pan, L.Y. TID characterization of 0.13 μm SONOS cell in 4 Mb NOR Flash memory. In Proceedings of the 19th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), Singapore, 2–6 July 2012.
  4. Hsieh, W.C.; Lee, H.T.; Jong, F.C. An Ionizing Radiation Sensor Using a Pre-Programmed MAHAOS Device. Sensors 2014, 14, 14553–14566. [Google Scholar] [CrossRef] [PubMed]
  5. Cheng, Y.H.; Ding, M.; Wu, X.L.; Xin, L.; Wu, K. Irradiation Effect of HfO2 MOS Structure under Gamma-ray. In Proceedings of the IEEE International Conference on Solid Dielectrics, Bologna, Italy, 30 June–4 July 2013.
  6. Oldham, T.R.; McLean, F.B. Total Ionizing Dose Effects in MOS Oxides and Devices. IEEE Trans. Nucl. Sci. 2003, 50, 483–499. [Google Scholar] [CrossRef]
  7. Wu, W.C.; Lai, C.S.; Wang, T.M.; Wang, J.C.; Hsu, C.W.; Ma, M.W.; Lo, W.C.; Chao, T.S. Carrier Transportation Mechanism of the TaN/HfO2/IL/Si Structure With Silicon Surface Fluorine Implantation. IEEE Trans. Electron. Devices 2008, 55, 1639–1646. [Google Scholar] [CrossRef]
Figure 1. (a) Cross-section view of F-MOHOS devices; (b) Charges generation and trapping states in the FAB-MOHOS device after gamma irradiation.
Figure 1. (a) Cross-section view of F-MOHOS devices; (b) Charges generation and trapping states in the FAB-MOHOS device after gamma irradiation.
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Figure 2. (a) The ID − VG curve for MOHOS device before and after 5 Mrad TID gamma irradiation; (b) The |delta VT| increase as a function of gamma irradiation TID for MOHOS device.
Figure 2. (a) The ID − VG curve for MOHOS device before and after 5 Mrad TID gamma irradiation; (b) The |delta VT| increase as a function of gamma irradiation TID for MOHOS device.
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Figure 3. (a) |Delta VT| for various F-MOHOS devices after 5 Mrad TID irradiation; (b) Relative charge density for various F-MOHOS devices after 5 Mrad TID irradiation.
Figure 3. (a) |Delta VT| for various F-MOHOS devices after 5 Mrad TID irradiation; (b) Relative charge density for various F-MOHOS devices after 5 Mrad TID irradiation.
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Figure 4. The VT vs. retention time for MOHOS device: (a) before gamma irradiation; (b) after 5 Mrad gamma irradiation.
Figure 4. The VT vs. retention time for MOHOS device: (a) before gamma irradiation; (b) after 5 Mrad gamma irradiation.
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Figure 5. The VT change with 10-years retention time for various F-MOHOS devices under VG = −4 V after (a) 0 Mrad gamma irradiation; (b) 5 Mrad gamma irradiation.
Figure 5. The VT change with 10-years retention time for various F-MOHOS devices under VG = −4 V after (a) 0 Mrad gamma irradiation; (b) 5 Mrad gamma irradiation.
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Table 1. MOHOS devices prepared with various F treated HfO2 as charge-trapping layer.
Table 1. MOHOS devices prepared with various F treated HfO2 as charge-trapping layer.
SplitNHFBFAFAB
Charge-trapping layerSi3N4HfO2HfO2HfO2HfO2
F treatmentnonoBefore HfO2 depositionAfter HfO2 depositionbefore and after HfO2 deposition

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MDPI and ACS Style

Hsieh, W.-C.; Lee, H.-T.D.; Jong, F.-C.; Wu, S.-C. Performance Improvement of Total Ionization Dose Radiation Sensor Devices Using Fluorine-Treated MOHOS. Sensors 2016, 16, 450. https://doi.org/10.3390/s16040450

AMA Style

Hsieh W-C, Lee H-TD, Jong F-C, Wu S-C. Performance Improvement of Total Ionization Dose Radiation Sensor Devices Using Fluorine-Treated MOHOS. Sensors. 2016; 16(4):450. https://doi.org/10.3390/s16040450

Chicago/Turabian Style

Hsieh, Wen-Ching, Hao-Tien Daniel Lee, Fuh-Cheng Jong, and Shich-Chuan Wu. 2016. "Performance Improvement of Total Ionization Dose Radiation Sensor Devices Using Fluorine-Treated MOHOS" Sensors 16, no. 4: 450. https://doi.org/10.3390/s16040450

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