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研究生： 楊富鈞
Yang, Fu-Chun
論文名稱： 以射頻濺鍍沉積二氧化鉿研製常關式氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體
Normally-off AlGaN/GaN Metal-Oxide-Semiconductor High Electron Mobility Transistors with RF-Sputtered Hafnium Oxide
指導教授： 王永和
Wang, Yeong-Her
學位類別： 碩士
Master
系所名稱： 電機資訊學院 - 微電子工程研究所
Institute of Microelectronics
論文出版年： 2018
畢業學年度： 106
語文別： 英文
論文頁數： 90
中文關鍵詞： 氮化鋁鎵/氮化鎵 、高電子遷移率電晶體 、閘極掘入 、射頻濺鍍沉積 、二氧化鉿
外文關鍵詞： AlGaN/GaN, high electron mobility transistor (HEMT), gate recess, RF sputter, HfO2
相關次數： 點閱：124  下載：17 
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    • 因為有寬能隙、高的強森優值(JFOM)以及好的載子傳輸特性優點，在未來的半導體發展中氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體是不可或缺的。然而，由於氮化鋁鎵/氮化鎵之間的晶格不匹配跟極化效應而產生的二維電子雲，因此元件操作在空乏型操作模式。在空乏型操作的電晶體有些許缺點，像是常開的狀態使得元件有額外的耗能，電路設計也更加複雜。因此，本論文中使用了閘極蝕刻技術去蝕刻閘極下方氮化鋁鎵的厚度。藉由氮化鋁鎵的厚度下降，二維電子雲濃度降低且操作模式轉變成增強型操作模式。為了降低元件閘極漏電流以及提升崩潰電壓的特性，我們以射頻濺鍍沉積二氧化鉿薄膜作為我們的閘極介電層。
    我們以射頻濺鍍沉積二氧化鉿薄膜以及閘極蝕刻完成增強型高電子遷移率電晶體。臨界電壓成功提升至 0.55 V，在閘極電壓為 4 V時，最大汲極電流密度達到 492 mA/mm，最大跨導值達到 176 mS/mm，次臨界擺幅與電流開關比為 141 mV/dec與 6.71 × 108，閘極漏電流有效降低至 6.65 × 10-5 mA/mm，三端崩潰電壓提升至 122 V。

    AlGaN/GaN high-electron-mobility transistors (HEMTs) are a candidate for future semiconductor development because of their wide bandgap, good Johnson’s figure-of-merit (JFOM), and good electron transport property. However, due to the lattice mismatch and the polarization effect of AlGaN/GaN, two-dimensional electron gas (2DEG) is formed at the interface of AlGaN/GaN. Therefore, the HEMTs operate in the depletion mode, which has some disadvantages, such as extra power consumption and complicated circuit design. In this work, the gate recess technique is used to etch the AlGaN barrier layer under the gate region. The 2DEG is reduced and the operation is changed to enhancement mode by decreasing the AlGaN thickness. In order to reduce the gate leakage current and enhance the breakdown voltage performance, RF-sputtered HfO2 is used as the gate dielectric. In this work, we present the E-mode MOSHEMT threshold voltage shifted to 0.55 V with the maximum drain current of 492 mA/mm at VG = 4 V. The transfer characteristics show a maximum transconductance of 176 mS/mm, a subthreshold swing of 141 mV/dec, and an on/off ratio of 6.71 × 108. The gate leakage current is 6.65 × 10-5 mA/mm and the three-terminal breakdown voltage is 122 V.

    中文摘要 I Abstract III CONTENTS VII List of Figures IX List of Tables IX Chapter 1 Introduction 1 1.1 Background 1 1.2 Motivation 4 1.3 Organization 9 Chapter 2 AlGaN/GaN Heterostructure 10 2.1 Lattice structure 10 2.2 Substrate material 11 2.3 Spontaneous polarization 13 2.4 Piezoelectric polarization 15 2.5 Two-dimensional electron gas 17 2.6 Modeling of AlGaN/GaN HEMTs 20 2.6.1 Drain current model 20 2.6.2 Simulation results 24 Chapter 3 Experimental Details 31 3.1 Gate recess process 31 3.1.1 Dry etching 31 3.1.2 Gate-recess depth 33 3.2 RF-sputter deposited HfO2 36 3.2.1 Properties of HfO2 36 3.2.2 RF sputter system and experiment 38 3.3 Experimental equipment 40 3.3.1 Spin coater 40 3.3.2 Mask aligner 40 3.3.3 ICP-RIE 40 3.3.4 E-gun evaporator 40 3.3.5 Rapid thermal annealing system 41 3.3.6 RF sputter system 41 3.3.7 Semiconductor analyzer 41 3.4 Device fabrication 46 3.4.1 Mesa isolation 47 3.4.2 Source and drain ohmic contact 48 3.4.3 Gate recess etching 49 3.4.4 HfO2 gate dielectric deposition 50 3.4.5 Gate Schottky contact 50 3.4.6 Post-metallization annealing 50 Chapter 4 Results and Discussion 54 4.1 Surface analysis of RF-sputtered HfO2 54 4.1.1 XPS measurement of unannealed HfO2 54 4.1.2 Surface analysis of unannealed HfO2 56 4.1.3 TEM 57 4.2 D-mode MOSHEMT performance 59 4.2.1 Saturation drain current 59 4.2.2 Transfer characteristics 60 4.2.3 Subthreshold swing and on-off ratio 61 4.2.4 Gate leakage current 62 4.2.5 Off-State Breakdown Voltage 63 4.3 E-mode MOSHEMT performance 65 4.3.1 Saturation Drain Current 65 4.3.2 Transfer Characteristics 67 4.3.3 Subthreshold Swing and On-Off Ratio 71 4.3.4 Gate Leakage Current 72 4.3.5 Off-State Breakdown Voltage 74 4.3.6 Pulse I-V Characteristics 75 4.3.7 Capacitance Measurement 77 4.3.8 Cutoff Frequency and Maximum Oscillation Frequency 78 4.3.9 Flicker Noise 80 Chapter 5 Conclusion 81 Chapter 6 Future Work 85 References 86

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