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研究生： 何承奕
Ho, Cheng-Yi
論文名稱： 半金屬與抬升式汲源極之二硫化鉬元件接觸工程
Contact Engineering for MoS2 Devices by Semimetals and Raised S/D
指導教授： 高國興
Kao, Kuo-Hsing
蘇俊榮
Su, Chun-Jung
學位類別： 碩士
Master
系所名稱： 電機資訊學院 - 奈米積體電路工程碩士博士學位學程
MS Degree/Ph.D. Program on Nano-Integrated-Circuit Engineering
論文出版年： 2022
畢業學年度： 110
語文別： 英文
論文頁數： 38
中文關鍵詞： 二硫化鉬 、半金屬 、邊緣接觸 、抬升式汲源極
外文關鍵詞： Molybdenum Disulfide (MoS2), Semimetal, edge contact, raised S/D
相關次數： 點閱：59  下載：22 
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    • 近年來，在元件尺寸不斷微縮的情況下即將達到了物理極限，原本基於矽的電子元件性能不再能顯著的提升，反而開始出現了許多問題。在製程方面遇到瓶頸時，研究學者開始積極往尋找新的替代材料著手，二維材料便是其中一個答案。在二維材料當中，又以過渡金屬二硫族化合物(TMDCs)最備受矚目，它具有低於奈米等級的厚度、高載子遷移率以及適當的能隙大小，因此被認為是能夠延續摩爾定律的新興材料。本文章致力於研究TMDCs中被廣泛討論的二硫化鉬(MoS2)。過高的接觸電阻一直都是二維材料所面臨的問題，因此我們透過了半金屬取代以往的金屬作為接觸，獲得了電性以及接觸電阻的改善，而後又透過選擇性成長的方式使汲極、源極上長出較厚的二硫化鉬，而通道區則長出較薄的二硫化鉬，以提升對元件的開關控制能力並同時達到降低接觸電阻的效用。
    在第三章中，我們探討了頂部接觸和邊緣接觸兩種不同元件結構的特性，並使用傳統的金屬-鈦和半金屬-銻作為接觸金屬。實驗結果表明利用銻作為接觸金屬的元件，無論是頂部接觸或是邊緣接觸都能夠有比較優異的電性表現，並且接觸電阻小於鈦的好幾倍。
    第四章我們提出了選擇性成長二硫化鉬的方法，於氧化鉿鋯(HZO)以及氧化鋁(Al2O3)上同時成長二硫化鉬，並發現長在氧化鋁上的二硫化鉬厚度要比長在氧化鉿鋯上的厚度薄，並具有鐵電的性質。同時，長在氧化鉿鋯上的二硫化鉬經過分析後證實具有摻雜效應且進一步的降低了片電阻值。透過此方法，我們將元件的汲極、源極區域設計為有氧化鉿鋯，通道區則是氧化鋁/氧化鉿鋯。實驗結果顯示我們成功的製備出在通道上較薄的二硫化鉬以及汲極、源極區上較厚的二硫化鉬，並達到良好的開關特性。

    In recent years, the physical limit has always been reached in the case of the continuous shrinking of the device size, and the performance of silicon-based electronic devices has not been improved significantly, but many problems have begun to appear. When encountering bottlenecks in the process, researchers began to actively search for new alternative materials, and two-dimensional materials were their answer. Among the two-dimensional materials, transition metal dichalcogenides (TMDCs) have attracted the most attention. They have a sub-nanometer thickness, high carrier mobility, and appropriate energy bandgap, so they are considered to be able to sustain Emerging Materials for Moore's Law. This article is devoted to the study of molybdenum disulfide (MoS2), which is widely discussed in TMDCs. High contact resistance has always been a problem faced by 2D materials. Therefore, we have improved the electrical properties and reduced contact resistance by replacing the precious metal as contact with semi-metal. Then, through selective enhanced growth, thicker MoS2 grows on the drain and source area, and thinner MoS2 grows on the channel area to improve the switching control ability of the device and reduce the contact resistance at the same time.
    In Chapter 3, we explore the properties of two different device structures, the top contact and edge contact, using conventional metal-titanium (Ti) and semimetal-antimony (Sb) as contact metals. The experimental results show that a device using antimony as the contact metal can have excellent electrical performance whether it is a top contact or an edge contact, and the contact resistance is several times lower than that of titanium.
    In chapter 4, we propose a method for selective enhanced growth MoS2. MoS2 was grown on hafnium zirconium oxide (HZO) and aluminum oxide (Al2O3) at the same time, it was found that the thickness of MoS2 grown on Al2O3 was thinner than that on HZO and have ferroelectric properties. Meanwhile, MoS2 grown on HZO was confirmed to have a doping effect after analysis and further reduce the sheet resistance value. Through this method, we designed the drain and source regions of the device to have HZO, and the channel region to be Al2O3/HZO. The experimental results show that we successfully prepared thin MoS2 on the channel and thick MoS2 on the drain and source regions to achieve good switching characteristics.

    摘要 I Abstract II 致謝 III Contents V Figure List VIII Table List X Chapter 1 INTRODUCTION 1 1-1 Background 1 1-2 Development of 2D-Materials 3 1-3 Applications and Challenges of 2D Materials 6 1-4 Motivation 7 Chapter 2 EXPERIMENT METHOD AND THEORY 8 2-1 Introduction of fabrication equipment and method 8 2-1-1 Chemical Vapor Deposition (CVD) 8 2-1-2 I-line (365 nm) stepper 9 2-1-3 Atomic Layer Deposition (ALD) 10 2-1-4 Physical Vapor Deposition (PVD) 10 2-1-5 Dry Etching 11 2-1-6 Lift-off process 11 2-2 Introduction of measuring instruments 12 2-2-1 Raman Spectroscopy 12 2-2-2 Transmission Electron Microscopy (TEM) 13 2-2-3 X-ray photoelectron spectroscopy (XPS) 14 2-2-4 X-ray Diffraction (XRD) 14 2-2-5 Electrical measurement system 15 2-3 Approaches to extract electrical properties 15 2-3-1 Y-Function Method (YFM) 15 Chapter 3 MoS2 transistors with top and edge contact 18 3-1 Motivation 18 3-2 Fabrication of the top and edge Contact devices 18 3-3 Materials Analysis 19 3-3-1 Transmission electron microscope (TEM) and Energy-dispersive X-ray spectroscopy (EDS) 19 3-4 Electrical performance of top and edge contact 20 3-4-1 Characteristics of common contact metal – Ti 20 3-4-2 Characteristics of contact semimetal – Sb 22 3-5 Summary 24 Chapter 4 SELECTIVE ENHANCED GROWTH & DOPING ON Al2O3 AND H0.5Z0.5O FOR RAISED MoS2 S/D 25 4-1 Motivation 25 4-2 Fabrication of Raised S/D MoS2 transistors 25 4-3 Materials Analysis 26 4-3-1 Raman spectroscopy 26 4-3-2 X-ray photoelectron spectroscopy (XPS) 27 4-3-3 Transmission electron microscope (TEM) and Energy-dispersive X-ray spectroscopy (EDS) 28 4-3-4 Sheet resistance (Rsh) 29 4-3-5 X-ray Diffraction (XRD) 31 4-4 Electrical performance of Raised S/D MoS2 transistors 31 4-5 Ferroelectric properties of raised S/D MoS2 transistor 33 4-6 Summary 34 Chapter 5 Conclusion 35 Reference 36   Figure List Fig. 1-1 Moore’s Law for semiconductors devices. 1 Fig. 1-2 Quantum tunneling effect. Illustrated is exponential damping of a wave function within a one-dimensional potential barrier, with Φ as the tunneling barrier high, EF as the Fermi levels of the metal electrodes, and s as the barrier width. 2 Fig. 1-3 (a) ID-VG transfer curves of an nMOSET influenced by short channel effects. (b) Schematic of the physical mechanisms of DIBL on MOSFETs. 2 Fig. 1-4 (a) Conventional bulk semiconductor, which surface is full of dangling bonds and thickness variation will lead to scattering of the charge carriers. (b) 2D material with a monolayer, covalently bonded lattice with uniform sub-nm body thickness and free of dangling bond surface. (c) the relations between mobility and thickness in bulk 3D and 2D materials. 3 Fig. 1-5 The formation of sp2 hybrids. 3 Fig. 1-6 Chart showing the library of 2D materials [17]. 5 Fig. 1-7 Schematic of the lattice structure of bulk and monolayer TMDs. (a) Top view of the monolayer TMD crystal (left) and the unit cell (right), clearly shows the spatial inversion symmetry breaking in monolayers. (b) Schematic of bulk and even-layer MX2 structure (left) and the unit cell (right), which has the inversion center located at the middle plane. 5 Fig. 1-8 (a) The band structure of metal-MoS2 that create MIGS and (b) band diagram at the contact with interface states, including tunnel barrier (van der Waals gap), orbital overlapped 2DMs under metal and defect states. These can modify the SBH and induce Fermi level pinning. 6 Fig. 2-1 shows the equipment used in this study and the schematic illustration of cold-wall CVD. 8 Fig. 2-2 shows the equipment used in this study and the schematic illustration of I-line stepper. 10 Fig. 2-3 shows the equipment used in this study and the schematic illustration of ALD [25]. 10 Fig. 2-4 shows the equipment used in this study and the schematic illustration of PVD. 11 Fig. 2-5 shows the equipment used in this study and the schematic illustration of dry etch process. 11 Fig. 2-6 (a) Flow chart of using the dry etching method to pattern the metal pad. (b) Flow chart of using lift-off process to pattern the metal pad. 12 Fig. 2-7 Basic principle of Raman spectroscopy. 13 Fig. 2-8 Principle of (a) TEM and (b) EDS. 13 Fig. 2-9 The working principles of XPS. 14 Fig. 2-10 Principle of the XRD. 15 Fig. 2-11 Diagram of Electrical measurement system. 15 Fig. 2-12 shows the linear relationship between Y function and gate voltage. 16 Fig. 2-13 With θ = 2µiCoxRcWL to extract the Rc from the strong inversion. 17 Fig. 3-1 (a) and (b) show the MoS2 transistor process flows of the top and edge contact scheme, respectively. (c) and (d) are corresponding structures. 18 Fig. 3-2 TEM images of the (a) top and (b) edge contact devices with Ti contact metal. 19 Fig. 3-3 TEM images of the (a) top and (c) edge contact devices with Sb contact semimetal. (b) and (d) are the corresponding EDS mapping images. 20 Fig. 3-4 Transfer curves (ID-VGS) of the top and edge contact with Ti contact metal. 21 Fig. 3-5 Schematics depict cross-sectional view for current flow path of the (a) top contact and (b) edge contact device. (c) and (d) are the top and edge contact band diagram of metal contact to MoS2, respectively. 21 Fig. 3-6 Transfer curves (ID-VGS) of top and edge contact with semimetal Sb. 23 Fig. 3-7 Schematics cross-sectional view for current flow path of the (a) top contact and (b) edge contact device. (c) and (d) are the top and edge contact band diagrams of semimetal contact to MoS2, respectively. 23 Fig. 3-8 Comparison with the (a) Rc and (b) Ion current improvement of the top and edge contact device with Ti and Sb. 24 Fig. 4-1 (a) and (b) are process flow and raised S/D MoS2 transistor structures, respectively. (c), (d) and (e) are other three different structures on the same wafer. 26 Fig. 4-2 Raman spectrum of MoS2 film on different substrates. 26 Fig. 4-3 (a)Hf 4f, (b)Zr 3d, (c)O 1s, (d)Mo 3d, (e)S 2p XPS spectra of the MoS2 film on 10 nm HZO and 10 nm Al2O3/10 nm HZO two different substrates. 28 Fig. 4-4 (a) illustrates the device structure of the HZO raised S/D MoS2 transistor. TEM images depict (b) thicker MoS2 grown on the S/D region and (c) thinner MoS2 on the channel region. 29 Fig. 4-5 Signal distribution of EDS mapping at channel region. 29 Fig. 4-6 shows the Rsh on HZO and Al2O3/HZO two different substrates (a) without and (b) with PDA before growing MoS2. 30 Fig. 4-7 shows the Rsh measurement of four different device structures on the same wafer. 30 Fig. 4-8 GI-XRD pattern of HZO. 31 Fig. 4-9 Transfer curves (ID-VGS) of (a) HZO contact with Al2O3 channel (b) HZO contact and channel (c) Al2O3 contact with HZO channel and (d) Al2O3 contact and channel four different structures, respectively. 32 Fig. 4-10 shows the (a) Ion increase and (b) Rc reduction compared with the MoS2 on HZO and MoS2 on Al2O3/HZO two devices. Inset in (a) is the best electrical performance of the two devices in this study. 33 Fig. 4-11 shows the (a) transfer curves (ID-VG) after 1 and 100 cycles measurements of the device (b) Vth value of forward and reverse curves and (c) difference in the Vth of forward and reverse curves. 34 Table List Table 3-1 Comparison of electrical properties of top and edge contact with metal Ti. 22 Table 3-2 Comparison of electrical properties of top and edge contact with semimetal Sb. 23 Table 4-1 The E12g and A1g mode frequency of MoS2 on 10 nm HZO and 10 nm Al2O3/10 nm HZO two different substrates. 27 Table 4-2 Atomic concentration of 10 nm HZO film. 28 Table 4-3 FWHM of Mo 3d and S 2p core level for 10 nm HZO film. 28 Table 4-4 FWHM of Mo 3d and S 2p core level for 10 nm Al2O3/10 nm HZO film. 28

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