5.1 Conclusion
In this dissertation, we have applied dual plasma treatment on MIS capacitor and Low-Temperature Polycrystalline-Silicon (LTPS) Thin Film Transistors (TFTs) with high-κ gate dielectric. In high-κ gate dielectric MIS capacitor, the characteristics of capacitance-voltage (C-V) and current-voltage (J-V) have been briefly described.
Second, the frequency dispersion and constant voltage stress (CVS) characteristics of the samples will be analyzed to estimate the improvement. Finally, current conduction mechanisms, such as Schottky emission, Frenkel-Poole (F-P) emission, and Fowler-Nordheim (F-N) tunneling have been discussed. Schottky barrier height, F-P barrier height, and F-N barrier height have been extracted. On the other hand, for high-κ gate dielectric LTPS-TFTs, the electrical improvements have been studied, including the hysteresis and the I-V characteristics. The device parameters, such as Vth, S.S., Gm,μeff,Dit,andNtrap have been extracted to study the improvement effect.
In chapter 2, the reliability properties and current conduction mechanisms of HfO2 gate dielectric films as a function of dual plasma treatment (the combination of CF4 pre-treatment and nitrogen post-treatment) have been investigated. First, the best conditions which decided form C-V and J-V characteristics were the samples treated by CF4 plasma for 10 sec and N2 (NH3) plasma for 120 sec. According to the current
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conduction analysis, the dominant current conduction mechanism was Schottky emission type in the region of low to medium electric fields (1.7 – 3.0 MV/cm);
Frenkel-Poole (F-P) emission operated in the region of medium to high fields (4.0 – 6.0 MV/cm); Fowler-Nordheim (F-N) tunneling was dominant at high fields (> 7 MV/cm). Dual plasma treatment was effective in improving interface quality, eliminating shallow trap levels, and enhancing reliability properties. In summary, the effect of dual plasma treatment could be better than single plasma treatment and dual plasma treatment would be an effective technology to improve the reliability of HfO2
thin films.
In chapter 3, the interface quality and reliability properties of HfAlOx gate dielectric with dual plasma have been verified. Based on above results, the electrical characteristics including C-V, I-V, hysteresis, frequency dispersion, and CVS characteristics of HfAlOx gate dielectrics could be great improved by dual plasma treatment. According to our study, the best condition is CF4 pre-treatment for 10 sec and N2 (NH3) post-treatment for 90 sec time. Based on the current conduction analysis, the dominant current conduction mechanism was Schottky emission type in the region of low to medium electric fields; Frenkel-Poole (F-P) emission operated in the region of medium to high fields; Fowler-Nordheim (F-N) tunneling was dominant at high fields. In conclusion, dual plasma treatment could improve interface quality and enhance reliability properties of HfAlOx thin films.
In chapter 4, the dual plasma treatment is successfully utilized on the LTPS-TFTs.
The electrical improvement has been studied, including the hysteresis and the I-V characteristics. The device parameters, such as Vth, S.S., Gm,μeff,Dit, and Ntrap are extracted to verify the improvement effect. It shows that the dual plasma samples have better electrical characteristics. Also, according to the 1/f noise (or flicker noise)
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measurement, dual plasma treatment could effectively reduce the grain-boundary trap-state densities at the channel and the oxide traps at the oxide/poly-Si interface.
Furthermore, the reliability properties and mechanisms of high performance HfO2 gate dielectric LTPS-TFT with dual plasma treatment are investigated, including PBS, NBS, and HCS. Also, the damage region induced by HCS is distinguished by the normal mode and reverse mode (S/D reverse) operation. In conclusion, the sample with dual plasma treatment has better stress immunity than the sample without treatment.
5.2 Suggestion for future work
In this dissertation, dual plasma treatment technology has been applied on MIS capacitor and Low-Temperature Polycrystalline-Silicon (LTPS) Thin Film Transistors (TFTs) with high-κ gate dielectric. The effect of dual plasma treatment on devices has been studied, including the electrical characteristics and reliability properties. Even so, there are some topics could be studied in the future:
1. Since the dual plasma treatment has been utilized on LTPS-TFTs in this dissertation, we could integrate the dual plasma treatment on novel devices in CMOS technology, such as Si-based MOSFET, Ge-based MOSFET, nanowire MOSFET, and FinFET et al.
2. In our experiment, the high-κ dielectric film was deposited by MOCVD system or Dual E-gun system. However, the ALD system is another technology to deposit high-κ dielectrics. We could utilize ALD system to deposit high-κ thin film.
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3. We could integrate silicide (NiSi) process as S/D of device to reduce the parasitic resistance. Besides, tradition junction formation at S/D requires high temperature annealing (i.e. 900~1000 oC). This high temperature process will make the high-κ dielectric crystallized. Therefore, we could combine implant to silicide (IIS) method to achieve low temperature dopant activation.
4. In our experiment, the TFTs were fabricated on the silicon substrate capped the thermal oxide layer. Hence, the dual plasma technology could be used for improving the quality of LTPS TFTs on glass substrate.
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個人學經歷資料表
姓名(中文): 張庭嘉
姓名(英文): Ting-Chia Chang 國籍: 台灣
出生地: 台中市 性別: 男
生日: 民國 72 年 11 月 28 日 學經歷: 高中: 國立嘉義高中
(1999.09 ~ 2002.06) 大學: 國立高雄大學電機工程學系
(2002.09 ~ 2006.06)
碩士: 國立交通大學電子研究所固態組(逕博) (2006.09 ~ 2008.01)
博士: 國立交通大學電子研究所固態組 (2008.02 ~ 2012.08)
學號: 9511564 博士論文題目:
中文: 雙重電漿處理技術應用於具高介電常數閘極絕緣層的金屬-絕緣層-半導 體電容及低溫多晶矽薄膜電晶體之特性研究
英文: Investigation of Dual Plasma Treatment Technology on MIS Capacitor and Low Temperature Polycrystalline Silicon Thin Film Transistor with High-κ Gate Dielectric