碩士 / 國立成功大學 / 微電子工程研究所 / 102 / Studies of reliability and low-frequency-noise of the FinFETs with different fin widths
Author : Min-Chih Chen
Advisors : Professor Yean-Kuen Fang
Professor Wen-Kuan Yeh
Professor Cheng-Li Lin
Electrical Engineering ＆ Institute of Microelectrinics
SUMARY
In this thesis, we mainly measured the basic electrical characteristics and reliability items including bias temperature instability and hot carrier effect. We also used the low-frequency-noise system to analyze the devices characteristics before and after the reliability tests. For the basic electrical characteristics, the thinner fin device has a better improvement in short channel effect but poor driving ability than that of the thicker device. Besides, the thinner fin device also has a higher quantum confinement effect, which gathers the inversion carriers toward the center of the fin body instead of the interface between the dielectric layer and the fin body, and thus called volume inversion. Based on this phenomenon, the thinner fin devices would suffer less characteristic degradations; because the inversion carriers gathering at the center of the fin body will become difficultly interact with defects in the dielectric layer. The thinner fin device suffers more characteristics degradation for its larger area of the depletion region in the center of the fin body. Besides, the volume inversion in a thinner fin device make it not significant coulomb scattering as found in the thicker fin device.
Key words: bias temperature instability, hot carrier effect, quantum confinement, low-frequency-noise
INTRODUCTION
FinFET is one of the most promising candidates for the next generation for its good improvement of short channel effect. Shrinking the fin width can improve the short channel effect, but the quantum confinement effect will be arisen. Although there were many simulation results showed the quantum confinement effect previously, but there are few measured data to prove this effect. In this thesis, we used low-frequency-noise, bias temperature instability and hot carrier test to analyze the different fin width of the devices characteristics.
MATERIALS AND METHODS
The samples we used were the bulk-silicon FinFET with the HfO2 as the dielectric layer and TiN as the metal gate. The size of the fin widths are 10 nm and 25 nm. The most critical gate length is 40 nm. The fin height is 30 nm. Followings are our measurement conditions for the n-type devices. For measuring ID-VG, the gate was added the ramp voltage from -1V to 1.5 V. The drain was fixed at voltage of 0.05 V and 1 V for devices working at the linear region and saturation region, respectively. The source and body were grounded. For the ID-VD measurements, the gate was added the overdrive voltages from 0.2 V to 1 V, while the drain was added the ramp voltage from 0 V to 1.5 V. The source and body were grounded. For the IG-VG measurement, the gate was added the ramp voltage from -1.5 V to 1.5 V. The drain, source and body were grounded. For bias temperature instability, the gate was fixed at a gate overdrive voltage of 1.6 V. The drain, source and body were grounded. In the hot carrier effect test, the gate was fixed at the gate overdrive voltage 1.5 V. In order to get the same electrical field in the channel of the different fin width, the drain was added at voltage of 1.64 V and 1.73 V, respectively for the thicker and thinner fin device. The source and body were grounded. In the reliability tests, the total stress time were 6000 seconds, and separated it in 5 cycles. Each cycle was followed by a set of basic I-V measurement. The low-frequency-noise, the gate was added from 0 V to 1.2 V. The drain was fixed at a voltage of 0.05 V, and grounded the source and body.
RESULTS AND DISCUSSON
Table 1 summary the hot carrier test and bias temperature instability results. In the hot carrier test, we can see the worse degradation in the thinner fin devices due to the volume inversion and the larger depletion region inside the fin body. The thicker fin devices are dominated by the interface inversion and thus have the worse degradation, because of the interaction between the dielectric traps and the interface inversion carriers. The thinner fin devices are the volume inversion dominating, hence a few carriers to interact with the dielectric traps.
Wfin/Lg (nm)
25/100 25/40 10/100 10/40
Items
RSD HCI_high Vd
10.22% 12.41%
PBTI 5.97% 2.46% 3.06% 1.63%
NBTI 24.24% 13.41% 16.04 8.85%
Table 1 The reliability items caused ID degradations
Thicker fin devices are dominated by the interface inversion, the inversion carriers that flowing in the channel easily interacts with the dielectric traps to cause the coulomb scattering. But thinner fin devices are the volume inversion dominating, the carriers can’t easily interact with the dielectric traps. With the coulomb scattering, the device would show the better linearity in the square root of input-referred voltage noise versus gate overdrive voltage plot that was showed in the following. From figure 1, we find the better linearity in the thicker fin devices than the thinner fin devices.
Figure 1. Square root of input-referred voltage noise versus gate overdrive voltage for n-type FinFETs with different fin widths.
CONCLUSION
In our study, the thinner fin devices improve the short channel effects obviously such as subthreshold swing, drain-induced-barrier-lowering and the threshold voltage roll-off. The thicker fin devices are dominated by the interface inversion, but the volume inversion dominates the thinner fin devices for the quantum confinement effect. Thus the thicker fin devices have worse degradation in the bias temperature instability due to their larger interaction of dielectric traps and the interface inversion carriers. In contrast, the thinner fin devices become worse degradation in the fixed-channel electrical field hot carrier test. This is owing to the larger depletion region inside the fin body instead of the interface between the dielectric layer and fin body. The volume carriers flow toward the larger depletion region to induce the worse degradation. In the low-frequency-noise analysis, the thicker fin devices are the interface inversion dominating, the inversion carriers interact with the traps in the dielectric layer more easily, so it can induce more obvious coulomb scattering.
| Identifer | oai:union.ndltd.org:TW/102NCKU5428010 |
| Date | January 2014 |
| Creators | Min-ChihChen, 陳旼志 |
| Contributors | Yean-Kuen Fang, 方炎坤 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 76 |
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