3.1 Introduction
3.3.2 The characteristics of carriers trapping/de-trapping
Figures 3-2 show the comparisons of the threshold voltage shift (ΔVth) for (a) HfSiON and (b) HfO2 under DNBTI stress with respect to stress time. Each cycle time is 1000 seconds and the stress temperature is kept at 100 oC. The gate voltage VG is -2.5 V under NBTI stress, and VG is 0, 1, 1.5V under passivated stress, respectively.
Furthermore, the terminals (source, drain, and substrate) are grounded under both conditions during the DNBTI stress. It is worth noting that the ΔVth is almost recovered at VG=1.5V. Figures 3-3 show the comparisons of the ΔVth on log scale for
(a) HfSiON and (b) HfO2 under first passivated stress. From the extraction of power law, one finds that there is only one power-law exponent value for the splits of VG=0 and 1V, but there are two distinct power-law exponent values for the split of VG=1.5V.
For the split of HfSiON, the n of power-law exponent value is from -0.173 to -0.456, and that of HfO2 is from -0.280 to -1.746. The decreasing magnitude of HfO2 is larger than that of HfSiON, and we suppose that the defects in HfO2 one more than that in HfSiON for electron trapping. Figures 3-4 show the comparison of that under second passivated period. For the split of HfSiON, Fig. 3-4(a), the n value of power-law exponent value is from -0.146 to -0.318, and that of HfO2 Fig. 3-4(b) is from -0.205 to -0.829. The decreasing magnitude of second passivated period is less than that of first passivated period, and the n value of third passivated period Fig. 3-5 is the smallest in these passivated states. In order to compare the difference recovered behaviors between different passivated and stress state, we extracted the coefficient n and summarized in TableⅠand Table ΙΙ. In the first passivated cycle, one can observe two different passivated behaviors for the split of VG=1.5V. In first stage, we speculate that the hole de-trapping from high-k dielectric to the substrate with small amount electrons trapping into high-k dielectric, which results in smaller n value. Then, the coefficient n decreases in second stage, because of a great amount of electrons trapped into dielectric. Furthermore, in the second passivated cycle, the absolute n values are
smaller than that in the first passivated cycle. Figures 3-6 depict the charge pumping current under the first NBTI stress cycle for (a) HfSiON and (b) HfO2 dielectrics, respectively. The charge pumping current increases during the first NBTI stress cycle.
However, during the first passivated stress cycle, the charge pumping current decreases slightly, as shown in Figs. 3-7. As compared with Figs. 3-2, the ΔVth would be almost recovered, especially for the split of VG=1.5V, but the charge pumping current isn’t recovered any more. Therefore, the recovery behavior isn’t due to the passivation of interface states, but due to the electrons trapping. Figures 3-8 depict the charge pumping current under the second NBTI stress cycle for (a) HfSiON and (b) HfO2 dielectrics, respectively. It is interesting that the charge pumping current doesn’t change, which is different from that during the first NBTI stress cycle. This means that the interface states increasing is close to saturation after the first NBTI cycle. In the second and third passivated/stress cycles of Figs. 3-8 to Figs. 3-11, the charge pumping current also decreases slightly. It turns out that, the recovery of ΔVTH is not dominant by the passivated behavior of interface states. Figures. 3-12 show the schematic of gate stack band diagram under (a) stress and (b) passivated cycle. Under NBTI stress state, holes in the inversion are injected into the gate dielectric layer.
Under passivated states, the electrons are injected into the gate dielectric layer, and the holes are slightly escaping from the gate dielectric at the same moment.
3-4 Summary
The threshold voltage shift was almost recovered at VG=1.5V, and there are two distinct power-law exponent values for the split of VG=1.5V. In addition, the charge pumping current increases only in the first NBTI cycle, and it almost has not any variation in other cycles due to the saturation of interface states generation. Therefore, we conclude that the interface states are generated at the first NBTI stress state, and they are not recovered anymore at passivation cycles. Under passivated stated, the recovery of ΔVTH is onlydue to the electrons/holes trapping/de-trapping.
0 1000 2000 3000 4000 5000 6000
0 1000 2000 3000 4000 5000 6000
-5
Figure 3-1 show the temperature dependence of (a)HfO and (b)HfSiON dielectrics.
(a)
(b)
0 1000 2000 3000 4000 5000 6000
0 1000 2000 3000 4000 5000 6000
-20
Figure 3-2 Threshold voltage shift during DNBTI stress (-2.5V)/passivated(0V, 1V, 1.5V) 1000s cycles at T=100oC on (a) HfSiON (b) HfO2 devices.
10 100 1000
Figure 3-3 Comparison of threshold voltage shift for (a) HfSiON and (b) HfO2
under first passivated period, and V =0, 1, 1.5V, respectively.
(b) (a)
10 100 1000
Figure 3-4 Comparison of threshold voltage shift for (a) HfSiON and (b) HfO2
under second passivated period, and VG=0, 1, 1.5V, respectively.
(b)
10 100 1000
Figure 3-5 Comparison of threshold voltage shift for (a) HfSiON and (b) HfO2
under the third passivated period, and V =0, 1, 1.5V, respectively.
(a)
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Figure 3-6 Charge pumping current under the first NBTI cycle for (a) HfSiON and (b) HfO2 dielectrics, respectively
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
(a)
(b)
Figure 3-7 Charge pumping current under the first passivated state at 1.5V for (a) HfSiON and (b) HfO2 dielectrics, and the appearances of recovery are not obviously.
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Figure 3-8 Charge pumping current under the second stressed state at -2.5V for (a) HfSiON and (b) HfO2 dielectrics, and the increase of charge pumping current are also not obviously.
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
(a)
(b)
Figure 3-9 Charge pumping current under the second passivated state at 1.5V for a) HfSiON and b) HfO2 dielectrics, and the recovered phenomenon almost can be ignored.
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
Figure 3-10 Charge pumping current under the third stressed state at -2.5V for (a) HfSiON and (b) HfO2 dielectrics, and the increase of charge pumping current are also not obviously.
(a)
(b)
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
passivate 10s passivate 50s passivate 100s passivate 200s passivate 500s passivate 1000s
(a)
(b)
Figure 3-11 Charge pumping current under the third passivated state at 1.5V for a) HfSiON and b) HfO2 dielectrics, and the recovered phenomenon almost can be ignored.
Figure 3-12 Schematic of gate stack band diagram under (a) stress and (b) passivated (b) (a)
Table Ⅰ Extracted Coefficient n during NBTI stress and ΔVth = K*tn. The NBTI stress voltage VG=-2.5V and the temperature T=100 oC.
Table Ⅱ Extracted Coefficient n during passivated oeriod, and ΔVth = K*tn. The NBTI stress voltage VG=-2.5V and the temperature T=100 oC.
Chapter 4 Conclusion
In this studying, the PBTI and NBTI degradation for HfO2 and HfSiON NMOSFETs with the metal gate electrode has been successfully demonstrated.
The pre-exist/generated oxide trap during PBTI stress will dominate the PBTI characteristics for Hf-based gate dielectrics. In addition, the better behaviors of threshold voltage degradation and oxide trap generation under PBTI stress indicates that the HfSiON thin film quality is better than HfO2 attributed to HfSiON gate dielectrics had the extra Si-O and Si-N bodings resulting in annihilation of oxygen vacancies. On the other hand, the electron trapping/de-trapping effect has been investigated in both HfO2 and HfSiON NMOSFETs with constant voltage stress. As compared with HfO2 dielectrics, the HfSiON has shallower charge trapping level under PBTI stress due to elimination of deep dielectric vacancies.
During the NBTI stress, the threshold voltage shift was almost recovered at VG=1.5V, and there are two distinct power-law exponent values for the split of VG=1.5V. In addition, the charge pumping current increases only in the first NBTI cycle, and it almost has not any variation in other cycles due to the saturation of interface states generation. Therefore, we conclude that the interface states are generated at the first NBTI stress state, and they are not recovered at any situation.
Under passivated stated, the recovery of ΔVth is only due to the electrons/holes trapping/de-trapping.
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Publication List
International Conference Paper：
[C-1] Wei-Liang Lin, Yao-Jen Lee, Wen-Cheng Lo, King-Sheng Chen,
Y. T. Hou4,K. C. Lin4, and Tien-Sheng Chao“Trapping and De-trapping Characteristics in PBTI and Dynamic PBTI between HfO2 and HfSiON Gate Dielectrics” 2008 INTERNATIONAL SYMPOSIUM ON THE PHYSICAL AND FAILURE ANALYSIS OF INTEGRATED CIRCUITS
簡 歷 (Vita)
姓名: 林威良
性別: 男
出生日: 1982 年 12 月 22 日
籍貫: 台灣
出身地: 台灣 台北市
學歷: 逢甲大學電子工程學系 學士班
20001 年 9 月-2006 年 1 月
國立交通大學電子物理研究所 碩士班
2006 年 9 月-2008 年 6 月
碩士論文題目:
閘極介電質氧化鉿與氮氧矽鉿之可靠度研究
Study on the Reliability of HfO2 and HfSiON Gate Dielectric