臺灣博碩士論文加值系統

傳統電晶體，當通道長度與閘極厚度不斷的持續微縮，將面臨到多晶矽的空乏層效應、高閘極電阻值、硼的穿隧效應………等問題。近年來，許多學者研究利用耐火金屬和金屬氮化物來取代傳統的多晶矽，金屬閘極有下列幾項需求(1)適合的功函數(2)低電阻值(3)高熱穩定性(4)製程整合與高介電材料的相容性。然而金屬化合物的功函數與材料本身晶格結構、結晶相、應力及最近很熱門的Fermi level pinning effect息息相關，所以公函數的調整將是一個很重要的課題。
此論文，將使用DC sputter系統，利用氮(Nitrogen)來調整鈦(Titanium)金屬的功函數。除了氮化鈦(TiNx)熱穩定性的研究外，我們也確實看到不同比例(0%~12%)的氮(Nitrogen)可調變鈦(Titanium)金屬的功函數(4.0eV~4.95eV)，而這功函數調變範圍涵蓋了整個矽能帶(Silicon bandgap)，使氮化鈦(TiNx)閘極能夠應用於NMOS與PMOS兩種元件上。
另外我們進而對氮化鈦(TiNx) Fermi level pinning effect進行探討。我們發現氮化鈦(TiNx)在二氧化矽(Silicon dioxide) 的Fermi level pinning effect上有兩種機制。首先，當氮化鈦(TiNx)的氮(Nitrogen)含量於2%~6%時，其金屬公函數pinned在約4.8eV;可是當氮化鈦(TiNx)的氮(Nitrogen)含量在10%~12%時，其金屬公函數是pinned約4.3eV。再者，我們第一次發現氮化鈦(TiNx)在二氧化鉿(Hafnium dioxide)介電層上並無Fermi level pinning effect。

As scaling of channel length and gate oxide thickness in conventional transistor, the refractory metal and metal nitride gates are used to replace the polysilicon gate due to poly-depletion effects, high gate resistance, and boron penetration. The requirements of metal gate are as following: (1)favorable workfunction (2)low sheet resistance (3)high thermal stability (4)compatibility with high-k dielectric and integration technology. However, the work function of materials are depends on crystal-orientation, stress and Fermi level pinning effect.
In this work, the work function of titanium (Ti) was modified by nitrogen (N2) in dc reactive sputtering system. The thermal stability of TiN was systematic investigated. With increasing N2 flow ratio from 0% to 12%, the work function of TiN was tuned from conduction band (4.0eV) to near valence band (4.95eV). It suggest that TiN films have tunable effective work functions appropriate for both NMOS and PMOS device.
In addition, we discuss the Fermi-level pinning effect of TiN/SiO2 and TiN/HfO2 gate stacks. For TiN/SiO2 gate stacks, we observe that the Fermi-level pinning effect is quite different for low and high nitrogen ratio. The work function for low N2 flow ratio of TiNx (2%~6%) was pinned at about 4.8eV, while pinned at about 4.3eV for the high one (10%-12%). For TiNx (2%~6%), there are extrinsic states between TiN and SiO2 interface after post metal anneal (PMA). For TiNx (10%~12%), we suggested that some nitrogen induced extrinsic states (NIES) near the silicon conduction band. Nevertheless, we did not observe any pinning effect at TiNx/HfO2 gate stacks.

Contents
Acknowledgment i
Chinese Abstract ii
English Abstract iii
Contents iv
Content of Figures vi
List of Tables ix
Chapter 1 Introduction……………………………….……………………….1
1.1 Background………………………………………………………1
1.2 The motivation in this study………………..……………………3
1.3 Thesis Organization………………………...……………………3
Chapter 2 The Characterization of Titanium Nitride Thin Film…….…..6
2.1 Introduction……………………………………………….……...6
2.2 Experiments……………………………………….……………..7
2.3 Results and Discussion…………………….…………………….8
2.3.1 N2 flow ratio effects on TiN thin films……………………8
2.3.2 The influence of RTA treatment………….………………...8
2.4 Summary……………………………………….………………..9
Chapter 3 The characterization of Titanium Nitride Metal Gate…….…20
3.1 Introduction……………………………………………….…….20
3.2 Experiments………………………………………….…………21
3.3 Results and Discussion………………………….……………...21
3.3.1 Nitrogen effect on work function modification……….….21
3.3.2 Crystal orientation effect on work function………………22
3.4 Summary………………………………………………….…….23
Chapter 4 The Fermi-level Pinning Effect of TiN Metal Gate……..……34
4.1 Introduction……………………………………………….…….34
4.2 Experiments………………………………………….…………35
4.3 Results and Discussion………………………….……………...36
4.3.1 Nitrogen Incorporation Effects on Fermi-Level Pinning…36
4.4 Summary………………………………………………….…….38
Chapter 5 Conclusions and Future Works....................................................59
5.1 Conclusions……………………………………….…………….59
5.1.1 TiN thin film……………………………………………..59
5.1.2 TiN gate electrode………………………….…………….59
5.1.3 The Fermi-level pinning effect of TiN gate electrode……60
5.3 Future works…………………

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