博士論文概要

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Graduate School of Advanced Science and Engineering Waseda University

博士論文概要

Doctoral Thesis Synopsis

論文題目

Thesis Theme

Study on Kinetics of

Nickel Silicidation of Silicon Nanowire and Its Application to Thermoelectric Device

申請者 (Applicant Name)

Shuichiro HASHIMOTO 橋本修一郎

Department of Nanoscience and Nanoengineering, Research on Nanomaterials Informatics

December, 2017

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【Outline】

A further miniaturization of electron devices raises an issue of a growing parasitic electric resistance. The author focuses on a metallization technique of nanowired-silicon (Si), and studied a kinetics of its solid-state chemical reaction. NiSi (nickel silicide) is well-known material having a relatively low resistance and low formation temperature. However, controlling the Ni silicidation rate of nanowired-Si still be a challenging issue. The author investigated the kinetics of Ni silicidation of Si nanowires by fabricating Ni-silicided nanowires, by evaluating the internal stresses, and by simulating the diffusivity of Ni in Si lattices. Eventually, it was found that the Ni silicidation rate is enhanced by a lattice disorder near the silicon dioxide (SiO2)/Si interface. The author firstly prepared Si nanowires fabricated by top-down processes with and without post-oxidation annealing (POA). Then, the author performed ultraviolet Raman spectroscopy analysis, which revealed that the internal stress was influenced by the thermal histories. Furthermore, the author conducted a molecular dynamics simulation for Si-Ni mixed system, which revealed that a deterioration of Si crystallinity is most plausible origin of the enhanced Ni diffusion rate. From these results, the author concludes that the deteriorated crystallinity along the SiO2/Si interface induces surface diffusion of Ni atoms and enhances the silicidation rate. Based on the knowledge about the kinetics of Ni silicidation reaction, the author newly manufactured thermoelectric (TE) energy harvester composed of Si nanowires. Miniaturized energy harvesters have recently begun to attract research attention to realize a long-lasting operation of autonomous sensors in smart infrastructures. The Nanowired-Si has been studied as superior TE material thanks to ultra-low thermal conductivity. The author fabricated Si-based scalable TE devices by employing a complementary-metal-oxide-semiconductor (CMOS) compatible process involving well-controlled Ni silicidation process. The author investigated the TE property, and found that TE power increased as nanowire length decreases. Furthermore, the TE performance was found to be very sensitive to the interface quality of SiO2/Si; interfacial trap charges along the SiO2/Si interface forms a potential barrier which reverses the sign of the Seebeck coefficient in n-type Si nanowires. The correct Seebeck coefficient is recovered with the hydrogen forming gas annealing. Finally, the author studied the electric property of the nanoscale metal/Si contact considering an image force effect, and the dielectric mismatch of SiO2/Si interface increasing the contact resistance at nanoscale metal/Si interface.

The dissertation is organized as follows. Chapter 1 introduces the background and the purpose. Chapter 2 highlights the Ni silicidation reaction of Si nanowires covered with SiO2 film, and reports an enhancement in the silicidation rate by changing thermal history. Chapter 3 and Chapter 4 address the origin of the enhanced silicidation rate by employing a Raman spectroscopy analysis and a classical molecular dynamics calculation, respectively. Following these studies on the kinetics of the Ni silicidation, development of Si-based TE energy harvesters is described in Chapter 5 and Chapter 6. Chapter 5 describes the fabrication of Si nanowire TE devices with Ni-silicide electrical contact, and investigation of the nanowire length dependency on TE properties.

Chapter 6 reports an anomalous TE property observed in Si nanowires covered with SiO2 film. Chapter 7 is a supplementary report on the electric characteristic of metal/Si contact in nanowires covered with SiO2 insulating film, especially considering the image force effect. Finally, Chapter 8 summarizes this dissertation.

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【Chapter 1: Introduction】

The motivation and the purpose of this dissertation were described in Section 1.1. Section 1.1.1 highlights an importance of a metallic silicide for miniaturized Si electron devices. Section 1.1.2 highlights miniaturized energy harvesters for massive-scaled sensor network for smart infrastructures, as a new application of Si nanowires. Section 1.1.3 describes a scalable architecture of Si nanowire TE generators with metallic silicide.

Finally, the organization of this dissertation is explained in Section 1.2.

【Chapter 2: Nickel silicidation of silicon nanowires covered with oxide film】

The author reports that the Ni silicidation rate differs in between the Si nanowires subjected to POA and not subjected to POA. Section 2.2.1 shows the fabrication procedure of the Si nanowires covered with SiO2 film.

Section 2.2.2 shows the procedure of the Ni silicidation process of the Si nanowires. In Section 2.3.1, the author reveals that the POA enhanced the surface Ni diffusion rate of the nanowires. In Section 2.3.2, the nanowires fabricated by the low-thermal-budget silicidation annealing shows that the preferential Ni diffusion along the SiO2/Si interface practically occurred in the early-stage of the Ni silicidation. One of the plausible origin of this enhancement, is POA-induced change in internal stress. However, changes in the stress was not thus far directly observed, which is left for further study in the following chapters. Section 2.4 summarizes this chapter.

【Chapter 3: Raman spectroscopy analysis of silicon nanowires】

An ultraviolet (UV) Raman spectroscopy analysis was performed to evaluate the lattice strain and extent of lattice disorder of the fabricated Si nanowires. Section 3.1 introduces the Raman spectroscopy method. Section 3.2 explains the UV Raman spectroscopy measurement system and the analysis method of the Raman spectra.

The author evaluated the uniaxial stress and the crystallinity of the nanowires with and without the POA treatment by using the modified Lorentzian function including the asymmetrical factor. In Section 3.3, the results of the Raman spectroscopy analysis that the compressive stress was increased by the POA treatment, and the Si crystallinity is deteriorated by the POA treatment. The origin of the POA-induced lattice disorder is attributed to a viscoelastic relaxation of the oxide-induced tensile stress within the nanowires. Thus, the enhanced Ni silicidation rate of the nanowires, is presumably considered to be originated from the following factors; i) a larger compressive strain, and ii) a deterioration of Si crystallinity along the SiO2/Si interface. However, the origin of the enhanced silicidation rate cannot be identified only by the Raman analysis. This issue is left for the molecular dynamics simulation described in the next chapter. Finally, Section 3.4 summarizes this chapter.

【Chapter 4: Molecular dynamics simulation of nickel diffusion】

A series of classical molecular dynamics (MD) calculation is performed to investigate the Si crystallinity dependency of an interstitial Ni diffusion rate in Si lattice. Section 4.1 introduces the MD simulation. Section 4.2 addressed the newly designed Stillinger-Weber (SW) potential parameters for Si-Ni mixed system. Section 4.3 highlights the simulation procedure. The MD calculations of Ni/Si/Ni stacks with different Si crystallinity, were performed. Section 4.4 describes the simulation results. The lattice strain is found to affect the diffusivity as follows; i) tensile strain increases the Ni diffusion coefficient, and ii) compressive strain decreases the Ni diffusion coefficient. Besides, the deteriorated crystallinity relatively increases the Ni diffusion coefficient. To

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further investigate the crystallinity dependency of the diffusivity, the author simultaneously performed a MD calculation of Si nanowires with an interstitial Ni atom, in Section 4.5. The potential energy landscapes for a interstitial Ni in the nanowires having different Si crystallinities, clearly indicated that the lattice disorder along the SiO2/Si interface plays a pivotal role of the enhancement in the Ni diffusion rate. Considering with the experimental results, the origin of the enhancement in the silicidation rate is considered to be the lattice disorder.

Section 4.5 summarizes this chapter. The present results suggest that a maintaining Si crystallinity in the nanowires is important for control of the silicidation process.

【Chapter 5: Silicon nanowire thermoelectric generators with nickel silicide】

A Si nanowire micro thermoelectric generator (μTEG) with Ni silicide was fabricated by a CMOS-compatible process. Section 5.1 highlights the newly designed Si-based μTEG architecture, as an introduction of this study.

Section 5.2 highlights the fabrication procedure of the μTEG. The μTEG were fabricated on a silicon-on-insulator wafer by electron beam lithography and dry etching. Section 5.3 explains the measurement system and evaluation method. Section 5.4 addressed the effect of narrowing nanowires on the TE performance.

Effective Seebeck coefficient, which is determined by the open circuit output voltage and the temperature difference across the Si nanowires measured by micro IR camera, is found to be enhanced by shortening the nanowires. The TE power generation density therefore increases in the miniaturized μTEG with shorter nanowires. The power density of the shorter nanowires is much more enhanced than that expected from the internal resistance. This enhancement can be attributed to the increase in effective Seebeck coefficient originated from a relatively steep temperature gradient in the nanowires. Finally, Section 5.5 summarizes this study.

【Chapter 6: Anomalous Seebeck coefficient of silicon nanowire covered with oxide film】

An anomalous TE characteristic of n-type Si nanowire μTEG was experimentally observed. Section 6.1 introduces the TE properties of Si nanowires. Section 6.2 highlights the fabrication procedure of the μTEG. Section 6.3 reports that the observed TE current is opposite to what is expected from the Seebeck coefficient of n-type Si. By hydrogen forming gas annealing, the normal TE property was recovered. In Section 6.4, the author discussed the origin of the anomalous Seebeck coefficient. Interfacial-trap-charges along the SiO2/Si interface surrounding the nanowires formed a potential barrier, and stimulated a diffusion of the majority carriers. Section 6.5 summarizes this chapter. The present results show the importance of the surface inactivation treatment of μTEGs to suppress the potential barrier and unfavorable contribution of minority carriers.

【Chapter 7: Image force effect on nanowired metal/silicon interface】

An influence of image force effect on electric characteristic of a nanowired metal/silicon interface, was computationally investigated. Section 7.1 introduces an influence of an external electric field on Si device performance. Section 7.2 explains the electrostatic calculation of Si nanowires covered with SiO2 film utilizing finite element method simulation. Section 7.3 reported the simulation results that the image potential lowers near the metals, whereas it rises in the proximity of the insulator. Finally, Section 7.4 summarizes this chapter.

【Chapter 8: Conclusion】

Chapter 8 finally summarizes and concludes the researches addressed in this dissertation.

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No.1

早稲田大学博士（工学）学位申請研究業績書

(List of research achievements for application of doctorate (Dr. of Engineering), Waseda University)

氏名橋本修一郎印

（As of November, 2017）種類別

(By Type)

題名、発表・発行掲載誌名、発表・発行年月、連名者（申請者含む）(theme, journal name, date & year of publication, name of authors inc. yourself)

学術論文

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学術論文

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学術論文

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学術論文

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学術論文

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学術論文

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学術論文

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学術論文

（連名）

国際会議

Shuichiro Hashimoto, Hiroki Kosugiyama, Kohei Takei, Jing Sun, Yuji Kawamura, Yasuhiro Shikahama, Kenji Ohmori, and Takanobu Watanabe, “Impact of Image Force Effect on Gate-All-Around Schottky Barrier Tunnel FET”, IEEE Xplore Digital Library, Proc. 2014 IEEE International Nanoelectronics Conference (INEC2014), p.1, 2014.

Shuichiro Hashimoto, Shuhei Asada, Taiyu Xu, Shunsuke Oba, Yuya Himeda, Ryo Yamato, Takashi Matsukawa, Takeo Matsuki, and Takanobu Watanabe, “Anomalous Seebeck coefficient observed in silicon nanowire micro thermoelectric generator”, Appl. Phys. Lett. 111.2, 023105, 2017.

Shuichiro Hashimoto, Ryo Yokogawa, Shunsuke Oba, Shuhei Asada, Taiyu Xu, Motohiro Tomita, Atsushi Ogura, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe,

“Enhanced nickelidation rate in silicon nanowires with interfacial lattice disorder”, J. Appl. Phys.

122.14, 144305, 2017.

Hiroki Yamashita, Hiroki Kosugiyama, Yasuhiro Shikahama, Shuichiro Hashimoto, Kohei Takei, Jing Sun, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “Impact of Thermal History of Si Nanowire fabrication process on Ni Silicidation Rate”, Jpn. J. Appl. Phys., 53.8, 085201, 2014.

Kohei Takei, Shuichiro Hashimoto, Jing Sun, Xu Zhang, Shuhei Asada, Taiyu Xu, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “ON Current Enhancement of Nanowire Schottky Barrier Tunnel Field Effect Transistors”, Jpn. J. Appl. Phys., 55.4S, 04ED07, 2016.

Takanobu Watanabe, Shuhei Asada, Taiyu Xu, Shuichiro Hashimoto, Shunsuke Oba, Yuya Himeda, Ryo Yamato, Hui Zhang, Motohiro Tomita, Takashi Matsukawa, Yoshinari Kamakura, Hiroya Ikeda, “A Scalable Si-based Micro Thermoelectric Generator” Electron Devices Technology and Manufacturing Conference (EDTM), p. 86, 2017.

Ryo Yokogawa, Shuichiro Hashimoto, Shuhei Asada, Motohiro Tomita, Takanobu Watanabe, and Atsushi Ogura, “Evaluation of controlled strain in silicon nanowire by UV Raman spectroscopy”, Jpn. J. Appl. Phys. 56.6S1, 06GG10, 2017.

Takuya Onishi, Shuichiro Hashimoto, Motohiro Tomita, Takanobu Watanabe, Kotaro Mura, Toshihiro Tsuda, Tetsuo Yoshimitsu, “Nano-scale Evaluation of Electrical Tree Initiation in Silica/Epoxy Nano-composite Thin Film”, Proc. International Symposium on Electrical Insulating Materials (ISEIM), pp. 359, 2017.

武良光太郎, 津田敏宏, 吉満哲夫, 大西拓弥, 橋本修一郎, 渡邉孝信, “回転機へのナノコンポジット適用に関する基礎的検討(Fundamental Study on Application of the Nanocomposite to an Electrical Rotating Machine),”電気学会論文誌Ａ（基礎・材料・共通部門誌）(IEEJ Transactions on Fundamentals and Materials), 137, 645, 2017.

Shuichiro Hashimoto, Hiroki Kosugiyama, Kohei Takei, Jing Sun, Yuji Kawamura, Yasuhiro Shikahama, Kenji Ohmori, and Takanobu Watanabe, “Impact of Image Force Effect on Gate-All-Around Schottky Barrier Tunnel FET”, International Nanoelectronics Conference (INEC2014), Sapporo, Japan, Jul. 28-31, 2014.

Shuichiro Hashimoto, Hiroki Kosugiyama, Kohei Takei, Jing Sun, Ryosuke Imai, Hiroki Tokutake, Motohiro Tomita, Atsushi Ogura, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “Impact of post-oxidation annealing of Si nanowire on its Ni silicidation rate”, 27th International Microprocesses and Nanotechnology Conference (MNC2014), Fukuoka, Japan, Nov. 4-7, 2014.

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No.2

早稲田大学博士（工学）学位申請研究業績書

種類別 By Type

国際会議

国内学会

Shuichiro Hashimoto, Kohei Takei, Jing Sun, Shuhei Asada, Taiyu Xu, and Takanobu Watanabe,

“Enhancement of Ni Diffusion Rate in Disordered Si Nanocrystal Studied by Molecular Dynamics Simulation”, The 6th NIMS/MANA-Waseda University International Symposium, Tokyo, Japan, Jul. 29, 2015.

Shuichiro Hashimoto, and Takanobu Watanabe, “A New Reactive Force Field for Study on the Formation of SiC/SiO2 Interface”, 2015 International Workshop on DIELECTIRC THIN FILMS FOR FUTURE ELECTRON DEVICES (IWDTF), Nov. 2-4, 2015

Shuichiro Hashimoto, Kohei Takei, Jing Sun, Shuhei Asada, Xu Zhang, Taiyu Xu, Toshihiro Usuda, Motohiro Tomita, Ryosuke Imai, Atsushi Ogura, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “Origin of Preferential Diffusion of Ni along Si/SiO2

Interface in Si Nanowire”, 28th International Microprocesses and Nanotechnology Conference (MNC2015), Toyama, Japan, Nov. 10-13, 2015.

Shuichiro Hashimoto, Shuhei Asada, Taiyu Xu, Shunsuke Oba, Takashi Matsukawa, and Takanobu Watanabe, “A Silicon Nanowire Thermoelectric Device Fabricated by Top-Down Process”, 14th European Conference on Thermoelectric (ECT2016), Lisbon, Portugal, Sep.

20-23, 2016.

Shuichiro Hashimoto, Shuhei Asada, Taiyu Xu, Shunsuke Oba, Takashi Matsukawa, and Takanobu Watanabe, “Anomalous Thermoelectric Characteristic of Silicon Nanowire Between Heavily Doped Silicon Pads”, 2016 International Conference on Solid State Device and Materials (SSDM2016), Tsukuba, Japan, Sep. 26-29, 2016.

Shuichiro Hashimoto, Shuhei Asada, Taiyu Xu, Shunsuke Oba, Takashi Matsukawa, and Takanobu Watanabe, “Dopant Distribution in Nickelided Si Nanowire Surrounded by SiO2 Film Characterized by Laser-Assisted Atom Probe Tomography”, 29th International Microprocesses and Nanotechnology Conference (MNC2016), Kyoto, Japan, Nov. 13-16, 2016.

橋本修一郎，川村祐士，鹿浜康寛，神岡武文, 渡邉孝信, “ショットキー障壁トンネルFETの伝達特性に鏡像効果が及ぼす影響”, 第60回応用物理学関連連合講演会, 神奈川工科大学, 厚木市, 神奈川県, 2013年3月.

橋本修一郎, 小杉山洋希, ソンセイ, 武井康平, 木谷哲, 図師知文, 渡邉孝信, “Ni シリサイド化速度のSi結晶構造依存性 -分子動力学法による解析-”, 第75回応用物理学秋季学術講演会, 同志社大学, 京田辺市, 京都府, 2014年9月.

橋本修一郎, 渡邉孝信, “SiCの酸化シミュレーションのための超離散ダイナミックボンドオーダー・ポテンシャルの開発”, 第29回分子シミュレーション討論会, 新潟国際会議場, 新潟市, 新潟県, 2015年12月.

橋本修一郎, 小花絃暉, 今津研太, 武井康平, 武良光太郎, 吉満哲夫, 渡邉孝信,

“走査型トンネル顕微鏡によるシリカ/エポキシ樹脂ナノコンポジット薄膜の表面観察”,

電気学会誘電・絶縁材料研究会, ルーテル市ヶ谷センター, 千代田区, 東京都, 2015年12 月,

橋本修一郎, 麻田修平, 徐泰宇, 大場俊輔, 松川貴, 渡邉孝信, “ナノワイヤ型シリコンデバイスで観測された逆向きの熱起電力”, 第77回応用物理学秋季学術講演会, 名古屋国際会議場, 名古屋市, 愛知県, 2016年9月.

橋本修一郎, 大場俊輔, 姫田悠矢, 大和亮, 松川貴, 松木武雄, 渡邉孝信, “SiO2絶縁膜界面の欠陥終端によるNanowire型Si熱電発電デバイスの特性改善,” 第78回応用物理学会秋季学術講演会, 福岡国際会議場, 福岡市, 福岡県, 2017年9月.

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No.3

早稲田大学博士（工学）学位申請研究業績書

種類別 By Type

国際会議 (連名)

国内学会 (連名)

Kohei Takei, Shuichiro Hashimoto, Jing Sun, Xu Zhang, Shuhei Asada, Taiyu Xu, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “ON Current Enhancement of Nanowire Schottky Barrier Tunnel FET”, 2015 International Conference on Solid State Device and Materials (SSDM2015), September 2015.

Shuhei Asada, Shuichiro Hashimoto, Kohei Takei, Jing Sun, Xu Zhang, Taiyu Xu, Toshihiro Usuda, Motohiro Tomita, Ryosuke Imai, Atsushi Ogura, Takashi Matsukawa, Meishoku Masahara, and Takanobu Watanabe, “Controlling Nickelidation Process of Si Nanowire by Ar+

Ion Irradiation”, 28th International Microprocesses and Nanotechnology Conference (MNC2015), Toyama, Japan, Nov. 10-13, 2015.

Taiyu Xu, Shuichiro Hashimoto, Shuhei Asada, Shunsuke Oba, Takashi Matsukawa, and Takanobu Watanabe, “Designing of a short leg thermoelectric generator on silicon”, 14th European Conference on Thermoelectric (ECT2016), Lisbon, Portugal, Sep. 20-23, 2016.

Shuhei Asada, Shuichiro Hashimoto, Xu Zhang, Taiyu Xu, Shunsuke Oba, Ryo Yokogawa, Motohiro Tomita, Atsushi Ogura, Takashi Matsukawa, and Takanobu Watanabe, “Impact of Ar+

Ion Irradiation on Nickelidation Reaction of Si Nanowire Covered with Oxide Film”, 29th International Microprocesses and Nanotechnology Conference (MNC2016), Kyoto, Japan, Nov.

13-16, 2016.

Ryo Yokogawa, Shuichiro Hashimoto, Shuhei Asada, Motohiro Tomita, Takanobu Watanabe, and Atsushi Ogura, “Evaluation of Controlled Strain in Silicon Nanowire by UV Raman Spectroscopy”, The 7th International Symposium on Advanced Science and Technology of Silicon Materials, Nov. 21-25, 2016.

Takanobu Watanabe, Shuhei Asada, Taiyu Xu, Shuichiro Hashimoto, Shunsuke Ohba, Yuya Himeda, Ryo Yamato, Hui Zhang, Motohiro Tomita, Takashi Matsukawa, Yoshinari Kamakura, Hiroya Ikeda, “A Scalable Si-based Micro Thermoelectric Generator”, 1st Electron Device Technology and Manufacturing Conference (EDTM2017), Toyama, Japan, Feb. 29, 2017,

Yuya Himeda, Shuichiro Hashimoto, Shunsuke Oba, Ryo Yamato, Takashi Matsukawa , Takanobu Watanabe, “Enhancement of Thermoelectric performance of p-type Short Silicon Nanowires,” 2017 International Conference on Solid State Devices and Materials (SSDM 2017), Sendai International Center, Sendai, Japan, Sep. 19-22, 2017.

Ryo Yamato, Shuichiro Hashimoto, Tianzhuo Zhan, Shunsuke Oba, Yuya Himeda, Takashi Matsukawa, Takanobu Watanabe, “Impact of Crystallinity of AlN Thermal Conductive Film on Thermoelectric Power of Silicon Nanowire Micro Thermoelectric Generator ” 2017 International Conference on Solid State Devices and Materials (SSDM2017), Sendai International Center, Sendai, Japan, Sep. 19-22, 2017.

武井康平, 小杉山洋希, 橋本修一郎, ソンセイ, 麻田修平, 徐泰宇, 若水昴, 松川貴, 昌原明植, 渡邉孝信, “酸化膜被覆型 Si ナノワイヤのシリサイド化に伴う破裂現象”, 第75回応用物理学秋季学術講演会, 同志社大学, 京田辺市, 京都府, 2014年9月.

木谷哲, 橋本修一郎, 武良光太郎, 今津研太, 小花絃暉, 神岡武文, 渡邉孝信, “分子シミュレーションによる Si表面の空孔クラスタと Ni原子の相互作用の解析”, 第75 回応用物理学秋季学術講演会, 同志社大学, 京田辺市, 京都府, 2014年9月.

大場俊輔, 橋本修一郎, 麻田修平, 徐泰宇, 松川貴, 渡邉孝信,“シリコンナノワイヤ型熱電発電デバイスにおける短チャネル効果”,電子デバイス界面テクノロジー研究会

-材料・プロセス・デバイス特性の物理(第 22 回)-, 東レ総合研修センター, 三島市, 静岡

県, 2017年1月.

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博 士 論 文 概 要

Graduate School of Advanced Science and Engineering Waseda University