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先進材料應用於低溫複晶矽薄膜電晶體和金氧半場效電晶體之研究

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電機學院微電子奈米科技產業研發碩士班

先進材料應用於低溫複晶矽薄膜電晶體和金氧半場效電晶體

之研究

A Study of Low-Temperature Polycrystalline Silicon Thin Film

Transistors and MOSFETs Using Advanced Materials

研 究 生:黃耀陞

指導教授:簡昭欣 教授

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先進材料應用於低溫複晶矽薄膜電晶體和金氧半場效電晶體之研究

A Study of Low-Temperature Polycrystalline Silicon Thin Film Transistors and

MOSFETs Using Advanced Materials

研 究 生:黃耀陞 Student:Yao-Sheng Huang

指導教授:簡昭欣 Advisor:Chao-Hsin Chien

國 立 交 通 大 學

電機學院微電子奈米科技產業研發碩士班

碩 士 論 文

A Thesis

Submitted to College of Electrical and Computer Engineering National Chiao Tung University

in partial Fulfillment of the Requirements for the Degree of

Master in

Industrial Technology R & D Master Program on Microelectronics and Nano Sciences

September 2009

Hsinchu, Taiwan, Republic of China

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i

先進材料應用於低溫複晶矽薄膜電晶體與金氧半場

效電晶體之研究

學生: 黃耀陞 指導教授: 簡 昭 欣 博士

國 立 交 通 大 學

電 機 學 院 產 業 研 發 碩 士 班

摘要 (中文)

在本論文中,我們利用了先進的高介電常數材料來製造高效能的低溫複晶矽薄膜電 晶體。擁有高效能 N 型通道薄膜電晶體以不同的高介電常數介電層材料:包括二氧化鉿 (HfO2)、矽酸鉿(Hf-silicate)、氧化鋁鉿(Hf-aluminum oxide)被提出,以有機

金屬高介電薄膜沉積系統沉積的高介電常數介電層在低溫環境中被製作出來,分別參雜 不同比例的矽或鋁組成比作為我們互相比較的主軸,並且研究其效應與可靠度。 我們發現高介電常數材料在電性上的表現有著普遍性的改善:包括 有較低的臨界電 壓、較好的次臨界擺幅、較高的驅動電流;在研究中,我們發現擁有複晶結構的二氧化 鉿 (HfO2)薄膜會導致較大的漏電流;相對地,矽酸鉿 (HfSiOx)薄膜則表現出比較優異 的熱穩定度,在高溫退火處理後仍維持其非晶狀態的結構。氧化鋁鉿 (HfAlOx)薄膜則 隨著鋁的參雜量越多,亦可提高其結晶溫度。當然,矽酸鉿薄膜相較於二氧化鉿薄膜較 低的介電常數,則為矽酸鉿薄膜的缺點。另外,具有較低介電常數的介面層自然形成於

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ii 高介電氧化層薄膜和矽基板之間,將會導致等效氧化層厚度降低的問題。 我們也研討了有關使用高介電薄膜當作閘極介電層的複晶矽薄膜電晶體所引起的 嚴重漏電流現象。我們認為高介電薄膜所產生的較高電場是引發嚴重的閘極誘發汲集漏 電流(GIDL)的原因,而場發射電流為其主要的漏電流機制。不同介電層的複晶矽薄膜電 晶體,其中矽酸鉿在目前的測試中展現了較佳的可靠度,主要原因在於其有較高的結晶 溫度、較好的薄膜品質與較少的介面狀態密度。 最後,我們嘗試將此新開發的高介電係數材料應用在金氧半場效電晶體,並且探討 較薄介電質層的結構和電性。

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iii

A Study of Low-Temperature Polycrystalline Silicon

Thin Film Transistors and MOSFETs Using

Advanced Materials

Student: Yao-Sheng Huang

Advisors: Dr. Chao-Hsin Chien

Industrial Technology R & D Master Program of

Electrical and Computer Engineering College of

National Chiao Tung University

ABSTRACT

In this thesis, advanced High-κ materials were employed to fabricate high performance low-temperature polycrystalline silicon thin film transistors (TFTs). High performance n-channel poly-Si thin film transistors (TFTs) are demonstrated using the different High-κ dielectric with hafnium dioxide (HfO2), hafnium silicate (HfSiOx) and hafnium aluminum

oxide (HfAlOx) layer are demonstrated by metal organic chemical vapor deposition system with low temperature processing. We compare with different composition ratio High-κ materials layer for our main shaft and the effect and reliability are also studied.

It is found the electrical characteristic of High-κ dielectric TFTs that improve obviously: including the lower threshold voltage, the better subthreshold swing, the higher driving current.

However, the large leakage current would be caused by the polycrystalline structure of HfO2 film. In contrast, HfSiOx films exhibit better thermal stability and retain the amorphous

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iv

structure even after high temperature annealing. In addition, as Al content increasing of HfAlOx films that could be to raise crystalline temperature. Certainly, the lower κ compared with HfO2 film is the disadvantage of the HfSiOx films. Besides, the native interfacial layer

with lower κ value always exists between the High-κ gate dielectric and Si substrate, which defeats the purpose of EOT lowering.

Moreover, the higher leakage current of poly-Si TFTs using High-κ gate dielectric was also studied. Aggravated gate-induced drain leakage (GIDL) current was thought to arise from the higher induced electric field by the introduction of High-κ films, and field-emission current would be the dominant leakage mechanism. We found the HfSiOx dielectric TFTs have the better reliability due to it has the better interface, higher crystalline temperature and lower density of states.

Finally, we also tried to apply the newly-developed High-κ films to the Metal-oxide semiconductor field-effect transistors (MOSFETs). And the structural and electrical properties of the thinner High-κ films were discussed.

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v

誌謝

在這兩年的研究所生活中,經由多人的協助,才能讓我順利完成我目前的研究,非 常感謝你們。首先要感謝我的指導老師簡昭欣教授,您在課業以及研究上給予我最大的 協助,並適時地幫我們指點迷津,也教導我們待人處事的道理,更會不時關心我們的生 活狀況,您是我研究所生活中的一大支柱。 其次要感謝NDML實驗室的大家,明瑞學長、志彥學長、兆欽學長、家豪學長、宜憲 學長、宇彥學長,還有竣承、効諭、欣哲、敬倫、弘森、猛飛、登緯、宣凱…等各位實 驗室學長,感謝各位學長不辭辛勞地在學業或是實驗上都給我很大的指導以及協助。謝 謝你們教導我如何使用實驗上的各種儀器設備,以及在專業知識領域上給予我適時指點 迷津,使我的研究能夠順利進展;還有,政庭、宗佑、柏錡、文朋同學和宏基、國永、 宗霖、禎晏學弟…等,謝謝你們陪我度過研究所的生活,以及對於我課業跟研究方面上 的幫忙,讓我在研究的路過程更加無往不利,才能有今日的成果。 再來要感謝在我實驗中一些的前輩,奈米中心的林聖欽先生、陳悅婷小姐、鄭淑娟 小姐、陳明麗小姐、黃國華先生、范秀鑾小姐、徐秀鑾小姐、黃月美小姐、葉雙得先生、 何惟梅小姐…等人;NDL元件代工:許倬綸先生、吳大維先生、魏耘小姐,分析組: 沈奕伶小姐、姚潔宜小姐、林宏旻先生、許瓊姿小姐,奈米元件量測:陳柏源先生、劉 汶德先生…等人。 另外在研究所的生活中,也要特別感謝其他實驗室泰瑞、哲緯…等學長們,耀峰、 信淵、誌陽、瑞桀、汶錦、佑寧…等同學們的幫忙以及照顧,除了課業上的切磋以及研 究方面的討論外,還有課餘的活動,例如打球、聚餐…等,都讓我的研究所生活增添了 很多額外的樂趣,也讓我結識到很多的同學及好朋友。有了這麼多同學的陪伴以及鼓勵, 讓我的研究所生活更加多采多姿。 還有很多很多不及備載,非常地感謝您們的協助讓我做研究的過程中沒有阻礙及實 驗上的經驗傳承。

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vi 最後,我要感謝在我的人生以及求學的路上全心全力支持我的父母,沒有您們對我 的細心呵護以及辛苦拉拔和關心,我也不會有今日的成就。真的很感謝您們在我求學路 上的支持,您們是我經濟跟精神上最強大的後盾,讓我沒有後顧之憂地專注在我的學業 上。在未來的日子裡,您們永遠是我的支柱,謝謝您們! 謹以此論文,獻給所有關心我的人以及我最親愛的家人!

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vii

Contents

Abstract (Chinese)……….……….…..….i Abstract (English)………...……….…....iii Acknowledge………...………..v Contents……….………..vii Table Captions……….………...x Figure Captions………..………....xii

Chapter 1 Introduction and Motivation……….………1

1-1 An Overview of Low-Temperature-Polycrystalline-Silicon (LTPS) Thin Film Transistors (TFTs) ……….……….………1

1-2 Motivation for improving Low-Temperature-Deposited Gate Dielectric Used in LTPS TFTs……….………..………3

1-3 Why do we use High-κ materials? ...4

1-4 Organization of the Thesis….……….……….………...5

Chapter 2 Characterizations of High-κ Films Deposited by Atomic-Vapor Deposition……..6

2-1 Introduction……….……6

2-2 Overview of Atomic-Vapor Deposition (AVD) System………....8

2-3 Structure and Electrical Characterizations of HfO2 and HfO2+HfSiOx-IL………...….9

2-3.1 Experiment……….9

2-3.2 Material Properties Extraction………...9

2-3.3 Structural Characterizations of High-κ Films by XPS Analysis...………..10

2-3.4 Chemical Bonding and Composition of High-κ Films by XRD analysis.…...11

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viii

2-4 Structure and Electrical Characterizations of HfSiOx Films..………..……...….12

2-4.1 Experiment………...…12

2-4.2 Material Properties Extraction……….13

2-4.3 Structural Characterizations of HfSiOx Films by XPS Analysis………13

2-4.4 Chemical Bonding and Composition of HfSiOx Films by XRD Analysis…….15

2-4.5 Structural Images of HfSiOx Films by TEM analysis……….……15

2-5 Structure and Electrical Characterizations of HfAlOx Films..…………..……….…..16

2-5.1 Experiment………...16

2-5.2 Material Properties Extraction……….…16

2-5.3 Structural Characterizations of HfAlOx Films by XPS Analysis…….………...17

2-5.4 Chemical Bonding and Composition of HfAlOx Films by XRD Analysis…….17

2-5.5 Structural Images of HfAlOx Films by TEM analysis………18

Chapter 3 High-Performance Low-Temperature-Compatible N-Channel Polycrystalline Silicon TFTs Using High-κ Materials………..….…….44

3-1 Introduction………….………..……….……….….…….44

3-2 High-κ Films Deposition and Device Fabrications……….…..……45

3-3 Device Electrical Parameters Extraction………..…46

3-4 Structural Characterization of High-κ Films……….…..…..47

3-5 Capacitance-Voltage Characteristic of High-κ Thick Films……….48

3-6 Electrical Properties of High-κ Thick Films………...………..50

3-7 Characteristic of Low-Temperature-Polycrystalline Silicon (LTPS) TFTs Using High-κ Gate dielectric……..………..….………..51

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ix

Chapter 4 High-Performance MOSFETs Using High-κ Materials………...…….73

4-1 Introduction………….………..……….……….73

4-2 High-κ Films Deposition and Device Fabrications……….73

4-3 Device Electrical Parameters Extraction……….…74

4-4 Structural Characterization of High-κ Films………....75

4-5 Characteristics of MOSFETs Using High-κ Gate Dielectric……….75

4-6 Electrical Properties of MOSFETs by Source/Drain Series Resistance Correction…76 4-7 Summary……….………..78

Chapter 5 Conclusion and Future Prospects………..………..92

5-1 Conclusion……….………..………….……….…………...92

5-2 Future Prospects………..….…93

References………95

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x

Table list

Chapter 2

Characterizations of High-

κ Films Deposited by Atomic-Vapor

Deposition

Table 2-1 Recipes of HfO2, HfSiOx and HfAlOx in Aixtron atomic-vapor deposition (AVD) system. p.20 Table 2-2 Summary of XPS extracted composition ratio of HfO2、HfSiOx、HfAlOx films,

Hafnium (Hf)、Silicon (Si)、Oxygen (O)、Aluminum (Al)deposited at 500℃ and PDA at 600℃, 24 h p.21 Table 2-3 Summary of XPS extracted composition ratio of HfO2、HfSiOx、HfAlOx films,

Hafnium (Hf)、Silicon (Si)、Oxygen (O)、Aluminum (Al) deposited at 500℃ and RTA at 900℃, 30s p.22 Table 2-4 Summary of thickness for the samples deposited at 500℃ and PDA at 600℃, 24h P23 Table 2-5 Summary of TEM-EDX composition ratio of HfO2+HfSiOx-IL stack structure,

Hafnium (Hf)、Silicon (Si)、Oxygen (O) deposited at 500℃ and PDA at 600℃, 24h p.24 Table 2-6 Summary of thickness for the samples deposited at 500℃ and rapid temperature annealing at 900℃, 30s p.25

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xi

Chapter 3

High-Performance Low-Temperature-Compatible N-Channel

Polycrystalline Silicon TFTs Using High-

κ Materials

Table 3-1 Summary of thickness, physical thickness, thickness deviation for

Low-Temperature Polycrystalline Silicon TFTs. p.53 Table 3-2 MOSCAP parameters vs. Device parameters . p.54 Table 3-3 Device parameters of Low-Temperature N-Channel Polycrystalline Silicon TFTs.

(W/L = 10μm/1μm) incorporating various dielectrics at VDS of 0.2V p.55

Chapter 4

High-Performance MOSFETs Using High-

κ Materials

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xii

Figure Captions

Chapter 1 Introduction and Motivation

Chapter 2 Characterizations of High-

κ Films Deposited by Atomic-Vapor

Deposition

Fig.2.1. Schematic diagram of atomic-vapor deposition (AVD) system p.26 Fig.2.2 XPS data of (a)Hf4f spectra, and (b)O1s spectra for HfO2 and HfO2+HfSiOx-IL

films deposited 400A by AVD. p.27 Fig.2.3 XPS data of (a)Hf4f spectra, and (b)O1s spectra for HfO2 film deposited 40A by

AVD. p.28 Fig.2.4 XRD spectra of HfO2 film deposited 400A by AVD.

PDA 600℃and 24h in N2 ambient. p.29

Fig.2.5 XRD spectra of HfO2+HfSiOx-IL films deposited 300A and 100A by AVD.

PDA 600℃and 24h in N2 ambient. p.29

Fig.2.6 XRD spectra of HfO2 film deposited 40A by AVD.

RTA 900℃and 30s in N2 ambient. p.30

Fig.2.7 Cross-sectional TEM images of TFTs incorporating HfO2 dielectric.

The thickness of HfO2 and IL are around 48.9nm and 1.5nm, respectively. p.31

Fig.2.8 Cross-sectional TEM images of TFTs incorporating two dielectrics of

HfO2+HfSiOx-IL. The thickness of HfO2, HfSiOx-IL and IL are around 37nm,

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xiii

Fig.2.9 TEM-EDX for composition ratios of Hf and Si from HfO2 dielectric on top

structure of Spectrum 2. p.32

Fig.2.10 Cross-sectional TEM images of TFTs incorporating two dielectric of

HfO2+HfSiOx-IL film. The thickness of HfO2, HfSiOx-IL and IL are around

37nm, 6.5nm and 1.0nm, respectively. (Spectrum 1) p.33 Fig.2.11 TEM-EDX for composition ratios of Hf and Si from HfSiOx-IL dielectric on

bottom structure of Spectrum1 p.33 Fig.2.12 Cross-sectional TEM images of TFTs incorporating HfO2 dielectric.

The thickness of HfO2 and IL are around 3.3nm and 2.0nm, respectively. p.34

Fig.2.13 XPS spectra of Hf4f for HfSiOx films deposited by AVD at various Hf/Si

composition ratios on Si (100). p.35 Fig.2.14 XPS spectra of Si2p for HfSiOx films deposited by AVD at various Hf/Si

composition ratios on Si (100). p.35 Fig.2.15 XPS spectra of O1s for HfSiOx films deposited by AVD at various Hf/Si

composition ratios on Si (100). p.36 Fig.2.16 XRD spectra of HfSiOx films deposited by AVD.

PDA 600℃and 24h in N2 ambient. p.36

Fig.2.17 XPS spectra of Hf4f for HfSiOx films deposited 40A by AVD at various Hf/Si

composition ratios on Si (100). p.37 Fig.2.18 XPS spectra of Si2p for HfSiOx films deposited 40A by AVD at various Hf/Si

composition ratios on Si (100). p.37 Fig.2.19 XRD spectra of HfSiOx films deposited 40A by AVD.

RTA 900℃and 30sec in N2 ambient. p.38

Fig.2.20 Cross-sectional TEM images of TFTs incorporating HfSiOx dielectric.

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xiv

Fig.2.21 Cross-sectional TEM images of TFTs incorporating HfSiOx dielectric.

The thickness of HfSiOx and IL are around 3.0nm and 1.6nm, respectively. p.39 Fig.2.22 XPS spectra of Hf4f for HfAlOx films deposited by AVD at various Hf/Al

composition ratios on Si (100). p.39 Fig.2.23 XPS spectra of Al2p for HfAlOx films deposited by AVD at various Hf/Al

composition ratios on Si (100). p.40 Fig.2.24 XPS spectra of O1s for HfAlOx films deposited by AVD at various Hf/Al

composition ratios on Si (100). p.40 Fig.2.25 XRD spectra of HfAlOx films deposited by AVD.

PDA 600℃and 24h in N2 ambient. p.41

Fig.2.26 XPS spectra of Hf4f for HfAlOx films deposited 40A by AVD at various Hf/Al

composition ratios on Si (100). p.41 Fig.2.27 XPS spectra of Al2p for HfAlOx films deposited 40A by AVD at various Hf/Al

composition ratios on Si (100). p.42 Fig.2.28 XRD spectra of HfAlOx films deposited 40A by AVD.

RTA 900℃and 30sec in N2 ambient. p.42

Fig.2.29 Cross-sectional TEM images of TFTs incorporating HfAlOx dielectric.

The thickness of HfAlOx and IL are around 3.6nm and 1.7nm, respectively. p.43

Chapter 3 High-Performance Low-Temperature-Compatible N-Channel

Polycrystalline Silicon TFTs Using High-

κ Materials

Fig.3.1 Schematic flow charts for the fabrication of poly-Si TFTs. p.56 Fig.3.2 Schematic flow charts for the fabrication of capacitors. P.59

Fig.3.3 Plots of capacitance density versus gate voltage.

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xv

Fig.3.3 Plots of capacitance density versus gate voltage.

(b) HfO2, HfO2+HfSiOx-IL and HfSiOx (66% Si) p.60

Fig.3.3 Plots of capacitance density versus gate voltage.

(c) HfSiOx incorporation of 25%, 40% and 66% Si p.61 Fig.3.3 Plots of capacitance density versus gate voltage.

(d) HfAlOx incorporation of ~7%, 12% and 40% Al p.61 Fig.3.3 Summary of hysteresis for High-κ materials.

(e) HfO2, HfSiOx-IL, HfSiOx and HfAlOx p.62

Fig.3.4 Summary of effective dielectric constant for High-k materials. p.62 Fig.3.5 Frequency dispersion of normalized capacitance versus gate voltage for

(a)HfO2 (b)HfO2+HfSiOx-IL films after annealing at 600℃,

24h in N2 ambient. p.63

Fig.3.6 Frequency dispersion of normalized capacitance versus gate voltage for HfSiOx incorporation of (a)66%, (b)40%, (c)25% Si after PDA at 600℃,

24h in N2. p.64

Fig.3.7 Frequency dispersion of normalized capacitance versus gate voltage for HfAlOx incorporation of (a)40%, (b)12%, (c)~7% Al after PDA at 600℃,

24h in N2. p.66

Fig.3.8 Leakage current density versus capacitance equivalent thickness for High-κ materials after PDA at 600℃, 24h in N2 ambient. p.68 Fig.3.9 Leakage current density versus breakdown filed for High-κ materials. p.68 Fig.3.10 The plot of ID-VG for HfO2, HfSiOx-IL (66% Si), HfSiOx (66% Si) and

HfAlOx (40% Al). p.69

Fig.3.11 Summary of GIDL effect for High-κ materials. p.69 Fig.3.12 Summary of threshold voltage for High-κ materials. p.70

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xvi

Fig.3.13 Summary of On/Off current for High-κ materials. p.70 Fig.3.14 Summary of interface density of state for High-κ materials. p.71 Fig.3.15 Summary of subthreshold swing for High-κ materials. p.71 Fig.3.16 Summary of field effect mobility for High-κ materials. p.72

Chapter 4 High-Performance MOSFETs Using High-

κ Materials

Fig.4.1 Schematic flow charts for the fabrication of MOSFETs. p.80 Fig.4.2 The plan-view Schematic for the fabrication of MOSFETs. p.81 Fig.4.3 Schematic flow charts for the fabrication of capacitors. p.82 Fig.4.4 Comparisons of transfer characteristics at VDS of 0.2 and 1.2V between

HfSiOx incorporation of 9% and 77% Si. p.83 Fig.4.5 Comparisons with various composition ratios of HfSiOx for subthreshold

swing. p.83 Fig.4.6 Comparisons of transfer characteristics at VDS of 0.2 and 1.2V between

HfAlOx incorporation of ~7% and 63% Al. p.84 Fig.4.7 Comparisons with various composition ratios of HfAlOx for subthreshold

swing. p.84 Fig.4.8 Comparisons with various High-κ materials for transfer characteristics at

VDS of 0.2 and 1.2V. p.85

Fig.4.9 Comparisons with HfO2, HfSiOx (12% Si) and HfAlOx (12% Al) for

subthreshold swing. p.85 Fig.4.10 Schematic for source/drain series resistance of HfSiOx (66% Si)

on MOSFETs. p.86 Fig.4.11 Comparison with threshold voltage correction between before and after

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xvii

Fig.4.12 Comparison with conductance correction between before and after condition on MOSFETs. p.87 Fig.4.13 Comparison with on/off current ratio correction between before and after

condition on MOSFETs. p.87 Fig.4.14 Summary of VTH correction at VDS of 0.1V for HfO2, HfSiOx and HfAlOx

films by RSD correction method. p.88

Fig.4.15 Comparison with various Al content in HfAlOx. p.88 Fig.4.16 Calculated fix charge with various Al content in HfAlOx. p.89

Fig.4.17 Summary of Ion correction at VDS=0.2V for HfO2, HfSiOx and HfAlOx

films by RSD correction method. p.89

Fig.4.18 Summary of Ioff correction at VDS=0.2V for HfO2, HfSiOx and HfAlOx

films by RSD correction method. p.90

Fig.4.19 Summary of Ion/ Ioff ratio correction at VDS=0.2V for HfO2, HfSiOx and

HfAlOx films by RSD correction method. p.90

Fig.4.20 Summary of thansconductance correction for HfO2, HfSiOx and HfAlOx

films by RSD correction method. p.91

Fig.4.21 Summary of mobility correction for HfO2, HfSiOx and HfAlOx films

by RSD correction method. p.91

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1

Chapter1

Introduction and Motivation

Low-temperature-polycrystalline-silicon (LTPS) thin-film-transistors (TFTs) have received much attention in recent years because of their increasing applications in active matrix displays (AMLCDs) [1.1]-[1.5], active matrix organic light emitting displays (AMOLEDs) [1.6]-[1.7], and memory devices [1.8]. Because of their better grain crystallinity, compared with the amorphous counterparts, higher carrier mobility and drive current can be achieved in poly-Si TFTs. The ability of fabricating high-performance LTPS TFTs enables their use in a wide range of new applications. Therefore, further improving the performance of LTPS TFTs is an interesting and important topic.

1-1 An Overview of Low-Temperature-Polycrystalline-Silicon (LTPS) Thin

Film Transistors (TFTs)

The study of polycrystalline silicon (poly-Si) thin film transistors (TFTs) fabricated below a maximum temperature of 600°C commenced in the 1980s. The original motivation was to replace quartz substrate with low-cost glass for active matrix display applications. In the beginning, the a-Si:H (hydrogenated amorphous silicon) TFTs were applied as the pixel switching device in the first-generation active matrix liquid crystal displays (AMLCDs). The major advantages of a-Si:H TFT technology are low processing temperature compatible with large-area glass substrate and low leakage current due to the high off-state impedance. However, because of the lack of short range order, the low carrier field-effect mobility (typically below 1 cm2/V-Sec) of a-Si:H TFTs limited their application to the switching elements only. Integration of driver circuits with display panel on the same substrate is very

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desirable because of the cost reduction in the module and reliability improvement of the system.

More recently, poly-Si TFTs are employed extensively in active-matrix liquid crystal displays because of their superior performance. The effective carrier mobility in poly-Si is significantly higher than that in a-Si, so the devices with reasonably high drive currents can be achieved in poly-Si TFTs. The higher drive-current allows smaller TFTs to be used as the pixel-switching elements, resulting in higher aperture ratio and lower parasitic gate-line capacitance for improved display performance. Previously, poly-Si TFT technology was primarily applied on small, high-definition LCD panels for projection display systems, however, the high processing temperature made it incompatible with commercial large-area glass substrates. With the rapid development of fabrication processes which are compatible with glass substrates in recent years, the manufacture of LTPS TFTs in AMLCDs on large-are substrates attracts more attentions. Modification of process procedure for enhancing TFT performance and reducing fabrication cost become an important issue in the fabrication of LTPS TFTs on large-area glass substrates.

Compared to the ultra-large scale integration (ULSI) process technology, the processes anddevice structures of LTPS TFTs are similar with metal-oxide-semiconductor field-effect-transistors (MOSFETs). The noticeable difference between LTPS TFTs and MOSFETs is that the former has to be performed at relatively low temperatures in order to be compatible with glass substrates. Due to this feature, only a-Si or poly-Si channels can be achieved on the glass substrate and the mobilities of a-Si and poly-Si are both much lower than that of c-Si (single-crystal silicon), which is widely used in conventional MOSFETs. Therefore, how to further increase the mobility of the low-temperature TFTs is one of the most important challenges. Among various process issues, the crystallization of a-Si thin films has been considered to be the most important process for fabricating high-performance

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LTPS TFTs. The crystallized poly-Si thin films always serve as active layer (i.e., channel) in the poly-Si TFTs. As a result, the quality of crystallized poly-Si films profoundly affects the performance of the poly-Si TFTs. In polycrystalline materials, most of defects are present in the grain boundaries. Enlarging grain size by various crystallization methods, such as solid phase crystallization (SPC), laser crystallization, and metal-induced crystallization (MILC), can reduce the grain boundaries and effectively promote the quality of poly-Silicon. The performance of devices can be improved through the high-quality poly-Si formed by crystallization technologies. Furthermore, other low-temperature process technologies of fabricating LTPS TFTs, such as gate dielectric formation, dopant activation, defect passivation, and device structures, are also essential for producing high-performance LTPS TFTs.

Finally, novel structure design is another approach to fabricate high-performance poly-Si TFTs. This technique focuses on the reduction of the electric field near the drain junction, and thus suppresses the device’s off-state leakage current. Many structures including multiple channel structures, offset drain/source, lightly doped drain (LDD), gate-overlapped LDD, field induced drain and vertical channel have been proposed and investigated intensively.

1-2 Motivation for improving Low-Temperature-Deposited Gate Dielectric

Used in LTPS TFTs

In the recently, the gate dielectric scaling down trended toward of the physical limitation (~1.0nm for SiO2) for International Technology Roadmap for Semiconductors (ITRS) [1.9]. It

extend a number of fundamental problems such high leakage current、low oxide breakdown voltage and low mobility…etc.

For TFTs, the key parameters of the LTPS TFTs are:(1) High mobility, (2) Low threshold voltage, and (3) High driving current and Low leakage current at high operate

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voltage. These are for demand of that to realize system-on-panel (SOP)、integrating driving ICs on the glass substrate and drive the liquid crystal. Using a thin dielectric can improve the driving current of TFTs. Similar to MOSFETs, however, the conventional gate dielectric (i.e. SiO2、Si3N4 ) for small dimension TFTs also need to decrease the thickness. Although

thinning down the gate oxide can increase the drive current of TFTs, however, the quality of low-temperature silicon oxide is not good enough, it results in higher gate leakage current.

However, the low-temperature-deposited oxide used in LTPS TFTs always exhibits poorer physical and electrical quality, such as high interface trap density, high gate leakage and low breakdown field, compared with high-temperature thermal grown oxide used in VLSI MOSFETs. Consequently, thicker gate oxide has to be used to prevent the high gate leakage current.

1-4 Why do we use High-

κ materials?

In order to preserve the physical dielectric thickness while increasing the gate capacitance, several new high-κ materials, including Al2O3, Ta2O5 were proposed

[1.10]-[1.11]. Among them, Al2O3 TFTs improvement is not sufficient due to the κ value is

not high enough. On the other hand, the Ta2O5 TFTs induce higher gate leakage current due to

its narrow band-gap.

In thesis, we fabricated the LTPS TFTs with High-κ gate dielectrics deposited by AVD system, including HfO2, HfSiOx and HfAlOx. Mainly, in addition to show the lower

threshold voltage,we want to discuss the influence of the different composition ratios of HfSiOx and HfAlOx films and reliability. Moreover, we hope to increase the driving current, decrease the threshold voltage of High-κ device and have high gate capacitance capability compared with conventional devices. Therefore, we found the better High-κ dielectric for LTPS TFTs that will show higher mobility, alleviated VTH roll-off, improved subthreshold

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swing, and increased on/off current ratio for n-channel Poly-Si TFTs.

Finally, we used the advanced materials as same as the LTPS TFTs on MOSFETs for thinner films. Then, the structure and electrical properties were discussed about various composition ratios influence.

1-5 Organization of the Thesis

In this thesis, the advanced High-κ materials were employed to fabricate the high-performance low-temperature polycrystalline silicon thin film transistors and metal- oxide-semiconductor field-effect transistors.

In Chapter 2, a new AVD system was the metal-organic chemical vapor deposition (MOCVD), dedicated to the deposition of the advanced high-κ films, was introduced briefly. Afterwards, we focused on the study in which HfO2 HfSiOx and HfAlOx films were

deposited under different pulse ratios using AVD system. Both structural and electrical characterizations of the High-κ films were presented. The effects of important deposition parameters, including the deposition temperature, the chamber pressure, oxygen gas flow, deposition frequency, and the composition adjustment, on the physical properties of as-deposited thin films were examined. Then the thermal stability of the High-κ films was studied with the help of post-deposition annealing (PDA) at high temperature.

In Chapter 3, high performance and low-temperature-compatible n-channel polycrystalline-Silicon TFTs were using High-κ materials.

In Chapter 4, high performance MOSFETs was using High-κ materials.

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Chapter2

Characterizations of High-

κ Films

Deposited by Atomic-Vapor Deposition

2-1 Introduction

As the dimensions of complementary metal oxide semiconductor (CMOS) devices are scaled into the nanometer regime, the gate dielectric thickness must also decrease to maintain a value of capacitance to reduce short channel effects and to keep device drive current at an acceptable level. The Semiconductor Industry Association's (SIA) International Technology Roadmap for Semiconductors (ITRS) indicates that by the years 2003-2005, the equivalent oxide thickness (EOT) of the gate dielectric decreases steadily to thinner than 1nm. Its leakage current under normal operation bias falls into the direct tunneling regime. For future generations of metal-oxide-semiconductor field-effect transistors (MOSFETs), the current gate oxide layer (SiO2 or SiOxNy) will need to be replaced with a new material possessing a

higher dielectric constant (κ >κSiO2=3.9).

High-κ materials are employed to increase the physical thickness of the gate insulator while maintaining the same EOT and gate capacitance, thus reduces significantly the tunneling leakage current. Although many High-κ materials are proposed to replace the conventional silicon dioxide (SiO2) as gate insulator, Hafnium dioxide (HfO2) is the most

promising candidate for its excellent advantages, such as a suitable dielectric constant (~25) [2.1], high band-gap energy (~ 5.9eV), and suitable tunneling barrier height for both electron and hole (>1eV). However, HfO2 is easily crystallized during deposition or following

annealing processes, and crystallization increases the leakage current via grain boundaries. In order to improve the relatively low crystallization temperature of around 600°C of pure HfO2,

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alloying HfO2 with SiO2 and Al2O3 has been proposed [2.2]-[2.3]. Since their silicon or

aluminum binary oxides, such as HfSiOx and HfAlOx, retain an amorphous structure after high temperature treatment, these binary oxides are now the most promising candidates to become the gate dielectric for next-generation MOSFETs [2.4]-[2.5].

Recently, High-κ materials have been investigated using several deposition techniques including physical vapor deposition (PVD) [2.4], atomic layer deposition (ALD) [2.9], plasma enhanced chemical vapor deposition (PECVD) [2.10], and jet vapor deposition (JVD) [2.11]. Although physical vapor deposition (PVD) is a simple technique for depositing new materials for evaluation in an academic organization, it may cause severe plasma damage to the electrical devices and is not preferred by industries because of poor step coverage and thickness uniformity. Chemical vapor deposition (CVD) has the advantages of uniform thickness over large substrate areas and good conformal step coverage. In contrast to ALD, it is relatively easy to dope the HfO2 using CVD, which may be necessary for future gate

dielectrics.

In this chapter, we employed the new atomic vapor deposition (AVD) system to deposit the High-κ films. The AVD system would be introduced briefly in section 2-2. Afterward, we focused on a study in which HfO2, HfSiOx and HfAlOx films were deposited under different

pulse ratios using AVD system. We present both structural and electrical characterizations of the High-κ films. First of all, the deposition and evaluation of HfO2 thin films have been

performed in section 2-3. In addition, we would hope to deposit simultaneously a stack structure to suppress interfacial layer growth. For example, a stack structure deposited two different High-κ dielectrics for a top gate oxide was HfO2 film and a under gate oxide was

HfSiOx film.

In the second part, the Si atoms incorporation into HfO2 films were investigated various

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the Al atoms incorporation into HfO2 films were investigated various composition ratios and

these results of HfAlOx films were discussed in section 2-5.

2-2 Overview of Atomic-Vapor Deposition (AVD) System

Figure 2-1 illustrates the schematic diagram of the AVD system. The main parts of the AVD system contain an AIXTRON horizontal reactor and a liquid-delivery TRIJET-TM vaporizer. Metal-organic precursors are used as the source of the High-κ film and kept at room temperature in liquid phase in a stainless tank. The precursor would be injected into the vaporizer via high-speed electro-mechanical valves and the injector plays the important role to control the injection amounts of the precursors. The injected amounts of the precursors can be controlled exactly by adjusting the injection numbers and opening time of individual injectors. In our experiment, the opening times of the injectors were all fixed at 0.8 msec. The injection periods and pulses can be adjusted to control the thickness and composition of the deposited films. The liquid precursor was injected to the vertical vaporizer and transferred from liquid type to gas type immediately. The temperature of vaporizer at 170℃could be introduced according to the kind of precursors. Argon gas would be used as carrier gas to carry the vaporized precursor into the reactor through the showerhead. The process gas, oxygen in our experiment, would be heated first in gas-box and then mixed with vaporized precursors in the showerhead. Finally, the mixed gases flowed to the process reactor and film deposition would take place on the hot substrate. The deposition parameters, including deposition temperature, chamber pressure, oxygen gas flow, injection frequency and pulse numbers, could be fine-tuned to obtain the adaptable films in different device applications. Among all process parameters, the substrate temperature is the key issue to affect the quality of the as-deposited films.

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2-3 Structure and Electrical Characterizations of HfO

2

and

HfO

2

+HfSiOx-IL

2-3.1 Experiment

HfO2 films were deposited by liquid-injection atomic-vapor deposition (AVD) system

and the liquid precursor was Hafnium(Tert-Butoxy)2(mmp)2, (Hf[OC(CH3)3]2(mmp)2, mmp:

OC(CH3)2CH2OCH3), which was dissolved in octane to make a 0.05 M solution. The

evaporation temperature of vaporizer was 170℃. Argon gas was used as the carrier gas, with a flow rate of 200 sccm, and oxygen as the oxidant with a flow rate of 1300 sccm. Substrate temperatures were 500℃, and the chamber pressures were 5 mbar. Prior to the deposition, the 6-inch silicon substrates were treated with standard RCA clean. After the cleaning process, the HF-treatment was to immerse wafers into a 100:1 diluted HF solution and then spun dry without rinse in DI water. Subsequently, wafers were put immediately into MOCVD for HfO2

and HfO2+HfSiOx-IL films deposition to prevent the native oxide formation. The thickness of

film was controlled by the injection pulse numbers. In addition, we split two cases of HfO2

film thickness for 40 nm (CaseⅠ) and 4 nm (CaseⅡ). Subsequently, caseⅠwas post deposition annealing (PDA) at 600℃ for 24h in N2 ambient of poly-Si TFT device and case

Ⅱ was rapid temperature annealing (RTA) at 900℃ for 30sec in N2 ambient of MOSFET

device. The deposition rate was extracted by measuring the thickness of thick HfO2 film with

N&K 1500 analyzer and anther thin film with an elliposmeter.

2-3.2 Material Properties Extraction

After film deposition, post deposition annealing (PDA) was performed on all samples to investigate its impact on material properties and electrical characteristics of HfO2 films. The

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x-ray photoelectron spectrum (XPS), grazing incidence x-ray diffraction spectrum (GI-XRD) and high resolution transmission electron microscopy (HRTEM).

In addition, the electrical characteristics of the HfO2 films were extracted from the

capacitors, low-temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) and metal-Oxide-semiconductor field-effect transistors (MOSFETs) device. For electrical analysis,

a precision impedance meter (Agilent 4284) was used for C-V measurements and a semiconductor parameter analyzer (Agilent 4156C) was used for I-V measurements.

2-3.3 Structural Characterizations of HfO

2

Films by XPS Analysis

In caseⅠ, chemical characterizations of HfO2 and HfO2+HfSiOx-IL films were

accomplished by x-ray photoelectron spectroscopy (XPS) utilizing monochromatic and standard Al x-ray source. The results are shown in Figures 2-2. In caseⅡ, the results are shown in Figures 2-3. Detected elements in thin films are hafnium (Hf), oxygen (O), and carbon (C). In order to avoid the undesirable carbon contamination on the sample surfaces, XPS analyses were also performed with ion milling. Negligible damage by low energy ions during depth profiling could be assumed since no significant shift of the binding energies is observed. It is found that the relative intensity of C1s signals decreases drastically after

sputtering.

Then, we would check Si spectra of our samples to compare with Si standard data base to correct XPS signals. This result is reasonable due to the fact that all air-exposed materials will have a thin film deposition, composed primarily of hydroxide (i.e., alcohol-type, C-OH units). After removing this thin layer, the signals originating from purer HfO2 can be obtained. This

phenomenon shows that the composition of HfO2 good chemical binary at the caseⅠand Ⅱ.

We calculated the atomic area of XPS data and sensitivity factor to extract the Hafnium and oxygen atomic ratio. For HfO2 film, Hf/O composition ratio = 1/2.3 in Table 2-1.

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2-3.4 Chemical Bonding and Composition of HfO

2

Films by XRD Analysis

After annealing at 600℃ for 24h in N2 ambient. Figures 2-4 to 2-5 show the GI-XRD

spectra of the HfO2 film and HfO2+HfSiOx-IL films, more sharp peaks, which are identified

to come from monoclinic polycrystalline structure, become more visible. The dominate phases of monoclinic polycrystalline structure are (110)、(-111)、(111)、(200)、(220). Among them, the intensity of (110)、(-111)、(200)、(220) phases at one layer HfO2 film were larger

than HfO2+HfSiOx-IL stack structure. On stack structure, the plane of (111) that density is

bigger than the other phases. The HfSiO-IL aids to slightly suppress the formation of monoclinic phase in HfO2 film.

After rapid temperature annealing at 900℃ for 30sec in N2 ambient. CaseⅡ in Figure

2-6 shows the monoclinic phases as same as the caseⅠ.

The disadvantages of polycrystalline thin films in the device applications are the large leakage current, device characterization lead to degrade.

2-3.5 Structural Images of HfO

2

Films by TEM analysis

Figure 2-7 shows the images of cross-sectional TEM for the HfO2 sample deposited at

500°C and the samples with subsequent post-deposition annealing at 600 ℃ for 24h in N2

ambient, respectively. The TEM samples of poly-Si TFT devices and MOSFET devices were fabricated by focus ion beam (FIB) method.

The test structures (gate-electrode/gate-dielectric/poly-Si channel) are included in the samples of TFT devices. In partⅠ, the lighter contrast is near the HfO2/poly-Si channel

interface. This interfacial layer is thought to be a Si-rich Hf silicate according to many previous reports, even though this speculation can be hardly identified by any compositional analysis method. The dark contrast is purer HfO2 film. The total physical thickness, the

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individual thickness of HfO2 film and interfacial layer are 48.9nm and 1.0nm, respectively

summary in Table 2-4. By the way, other problem to the upper interface between gate-electrode and HfO2 was rough. This could be caused by contact badly and induced

leakage paths.

In partⅡ, Figure 2-8 shows the images of cross-sectional TEM for the stack structure. A bottom layer HfSiOx film deposited100A at 500°C. Subsequently, a upper layer HfO2 film

deposited 300A at 500℃. The samples with subsequent post deposition annealing at 600℃ for 24h in N2 ambient. The total physical thickness, the individual thickness of HfO2 film,

HfSiOx-IL and interfacial layer are 37nm, 6.5nm and 1.0nm, respectively summary in Table 2-4. Figures 2-9 , 2-11, which were identified by TEM energy-dispersive spectroscopy (EDS) in Table 2-5 lists the element ratios of Hf, Si and O in bright (Spectrum1) and dark (Spectrum2) regions separately.

Figure 2-12 shows the images of cross-sectional TEM for caseⅡ. The light region was an interface layer between HfO2/Si. Physical thickness of HfO2 film and IL were 3.3nm and

2.0nm, respectively summary in Table 2-6.

2-4 Structure and Electrical Characterizations of HfSiOx Films

2-4.1 Experiment

In this section, we focus on the deposition and evaluation of HfSiOx films. HfSiOx films were deposited by liquid-injection atomic vapor deposition (AVD) and the liquid precursors were Hf[OC(CH3)3]2(mmp)2 and Si[OC(CH3)3]2(mmp)2 respectively; both are dissolved in

octane to make a 0.05M solution. Form the reference process parameters for HfSiOx thin films deposition (deposition temperature = 500℃, chamber pressure = 9 mbar, oxygen gas flow = 1800 sccm, Argon gas flow = 200 sccm, injection frequency = 1Hz). It is well known

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that the Si precursor usually needs higher processing temperature for the film deposition. In order to have a more detailed surveillance over the influence of stoichiometric ratio on the properties of thin films, deposition temperature 500℃, injection frequency 1 Hz, and the pulse ratios (Hf/Si pulse ratios = 1/1, 5/1, 10/1) were executed separately.

In case Ⅱ, HfSiOx thin films deposited various pulse ratios (Hf/Si pulse ratios = 1/2, 1/1, 5/1, 10/1, 20/1, 30/1) were executed separately.

2-4.2 Material Properties Extraction

After film deposition, post deposition annealing (PDA) was also performed on all samples to investigate its impact on material properties and electrical characteristics of HfSiOx films. The fundamental physical properties of thin films were analyzed by many techniques, such as x-ray photoelectron spectrum (XPS), grazing incidence x-ray diffraction spectrum (GI-XRD), and high resolution transmission electron microscopy (HRTEM). Furthermore, the electrical properties of HfSiOx films were also extracted from the capacitors with MOS structure.

For electrical analysis, a precision impedance meter of model Agilent 4284 was used for C-V measurements and a semiconductor parameter analyzer of model Agilent 4156C was used for I-V measurements.

2-4.3 Structural Characterizations of HfSiOx Films by XPS Analysis

Figures 2-13 to 2-15 show the spectra of Hf4f, Si2p, and O1s as a function of

Hf/Si pulse ratios: Hf/Si ratio= 1/1, 5/1, 10/1. From Figure 2-13 of Hf4f, we found that pure

hafnium oxide shows two clearly separated peaks and becomes broader as the concentration of Si increases. These broad peaks are caused by additional created-peaks when the

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concentration of Si increases. The binding energy of Hf-O bond monotonically increases with increasing concentration of Si. It means that more and more Si-O bonds are formed as the Si ratio increases, so the peak shifts to the higher binding energy. The same trends have been seen in the binding energy spectra of Si2p and O1s states, shown in Figures 2-14 to 2-15.

Typical values of the binding energy of Si2p and O1s states are around 103.2 eV and 532.8 eV

for silicon dioxides, respectively. As the amount of Hf increases, the peaks of Hf4f shift from

17.0 eV to 16.5 eV , the peaks of Si2p shift from 102.0 eV to 101.7 eV and the peaks of O1s

shift from 531.3 eV to 530.2 eV. These shifts mean that oxygen prefers to bind with Si than Hf, so more and more Si-O bonds are formed. When Hf/Si atomic ratio in corporation to HfSiOx films increased, we found XPS spectra of Si2p intensity decreased right.

CaseⅡ in Figures 2-17 to 2-18. Figure 2-17 shows Hf4f spectra, the Hf atomic intensity

decreased as Si atoms incorporations were increasing. The Hf-O bond was good and spectra were not shift obviously. Figure 2-18 shows one strong peak and one weak peak located at 102.2 eV and 97.6 eV are found in Si-bulk and HfSiOx (Hf/Si=1/2, 1/1, 5/1, 10/1, 20/1, 30/1) films. These are Si peaks coming from Si substrate in XPS measurements due to the thinner films of these two samples.

This result is also consistent with our XPS spectra described above. Nevertheless, the HfSiOx films retain amorphous structure and exhibit better thermal stability than HfO2 film

after high temperature annealing, which is beneficial for device applications. We calculated the atomic area of XPS data and sensitivity factor to extract the Hafnium and silicon atomic ratio. Si atoms incorporation into HfSiOx films, the composition ratios (77%, 66%, 40%, 25%, 12%, 9% Si) taken the place of pulse ratios (Hf/Si pulse ratios = 1/2, 1/1, 5/1, 10/1, 20/1, 30/1) in Table 2-2 and 2-3.

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Analysis

Figure 2-16 shows GI-XRD spectra of HfSiOx films of caseⅠwith Hf/Si composition ratios (25%, 40%, 66% Si) deposited at 500℃ and subsequent to PDA at 600℃ for 24h in N2 ambient. For the spectra of these measured samples, we didn’t find any signal besides

substrate signal. We believe that the HfSiOx films deposited with these parameters exhibit amorphous structures which were preferred from the viewpoint of suppressing leakage current and better thermal stability during device fabrications, compared with HfO2 films.

Figure 2-19 shows GI-XRD spectra of HfSiOx films of caseⅡwith Hf/Si composition ratios (9%, 12%, 25%, 40%, 66%, 77% Si) deposited at 500℃ and subsequent to RTA at 900 ℃ for 30sec in N2 ambient. We found crystalline phases as less Si incorporations of 40%, the

dominant phase were monoclinic and orthorhombic structures.

2-4.5 Structural Images of HfSiOx Films by TEM Analysis

Figure 2-20 shows the images of cross-sectional TEM for the as-deposited HfSiOx film with Hf/Si composition ratio (66% Si) deposited at 500℃, the sample with subsequent post deposition annealing at 600℃ for 24h in N2 ambient, respectively. Both of top and bottom

interfaces were smooth for HfSiOx film which could be better electrical properties. The individual thickness of HfSiOx films and interfacial layer are 34.6nm and 1.0nm respectively summary in Table 2-4.

Figure 2-21 shows the images of cross-sectional TEM for caseⅡ. The light region was an interface layer between HfSiOx/Si. Physical thickness of HfSiOx film was 3.0nm and interfacial layer was 1.6nm. Summary of thickness was in Table 2-6.

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2-5 Structure and Electric Characterizations of HfAlOx Films

2-5.1 Experimental

In this section, we focus on deposition and evaluation of HfAlOx films. HfAlOx films were deposited by liquid-injection atomic vapor deposition (AVD) and the liquid precursors were Hf[OC(CH3)3]2(mmp)2 and Al[OCH(CH3)2]3. Both precursors were dissolved in octane

to make a 0.05M solution. Form the process parameters for HfAlOx thin films deposition (deposition temperature = 500℃, chamber pressure = 5 mbar, oxygen gas flow = 1300 sccm, Argon gas flow =200 sccm, injection frequency = 1Hz). In order to have a more detailed surveillance over the influence of stoichiometric ratio on the properties of thin films, deposited pulse ratios (Hf/Al pulse ratios = 1/1, 5/1, 10/1) were executed separately. After film deposition, post deposition annealing (PDA) was also performed on all samples to investigate its impact on material properties and electrical characteristics of HfAlOx films.

In case Ⅱ, HfAlOx thin films deposited various pulse ratios (Hf/Al pulse ratios = 1/2, 1/1, 5/1, 10/1) were executed separately.

2-5.2 Material Properties Extraction

The fundamental physical properties of thin films were analyzed by many techniques, such as x-ray photoelectron spectrum (XPS), grazing incidence x-ray diffraction spectrum (GI-XRD), and high resolution transmission electron microscopy (HRTEM). Furthermore, the electrical properties of HfAlOx films were also extracted from the capacitors with MOS structure. For electrical analysis, a precision impedance meter of model Agilent 4284 was used for C-V measurements and a semiconductor parameter analyzer of model Agilent 4156C was used for I-V measurements.

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2-5.3 Structural Characterizations of HfAlOx Films by XPS Analysis

Figures 2-22 to 2-24 show the spectra of Hf4f, Al2p, and O1s as a function of

Hf/Al composition ratios: Hf/Al ratio= 1/1, 5/1, 10/1. Typical values of the binding energy of Al2p and O1s states are around 74.4 eV and 532.8 eV for aluminum oxides, respectively. From

Figures 2-22 to 2-23 show as the amount of Hf increases, the peaks of Hf4f weren’t shift for

16.5 eV , the peaks of Al2p shift from 73.3 eV to 73.6 eV and the peaks of O1s shift from

529.9 eV to 530.0 eV. As Hf/Al composition ratios in corporation to HfAlOx films increased, we found XPS spectra of Al2p intensity decreased.

As same as the XPS spectra for caseⅡ, Figures 2-26 to 2-27 show the spectra of Hf4f and

Al2p as a function of Hf/Al composition ratios: Hf/Al ratio= 1/2, 1/1, 5/1, 10/1.

This result is also consistent with our XPS spectra described above. We calculated the atomic area of XPS data and sensitivity factor to extract the Hafnium and aluminum composition ratio, Al atoms incorporation into HfAlOx films, the composition ratios (63%, 40%, 12%, ~7% Al) taken the place of pulse ratios (Hf/Al pulse ratios = 1/2, 1/1, 5/1, 10/1) in Table 2-2 and 2-3.

2-5.4 Chemical Bonding and Composition of HfAlOx Films by XRD

Analysis

Figure 2-25 shows GI-XRD spectra of HfAlOx films with Hf/Al composition ratios (~7%, 12%, 40% Al) deposited at 500℃ and subsequent to PDA 600℃ for 24h in N2

ambient. For the spectra of these measured samples, we found crystallization phases for less

Al incorporation of 40% Al into HfAlOx film. We saw that as Al atoms increased incorporation into HfAlOx films, the crystallization temperature would to be raised [2.12].

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content into HfAlOx film, we got the monoclinic and an amount of small cubic-like phases. We considered two cases of the dielectric constant for HfAlOx films with Hf/Al composition ratios (~7% and 12% Al). We employ the Clausius-Mossotti relation for that analysis[2.13].

The Clausius-Mossotti relation is expressed as follows:

κ

=

1 + (8παm/3Vm)/(1 − 4παm /3Vm) ..……..…… (1)

Here, κ, αm and Vm are the κ-value, molar polarizability and the molar volume, respectively.

In Eq. (1), αm increase or Vm shrinkage bring about the κ-value enhancement. Although it is

difficult to determine the accurate αm value experimentally, Vm values can be evaluated from

the lattice parameters determined by XRD. The αm value concern about High-κ dielectric

nature and the Vm value concern about deposition system, surface treatment, post deposition

annealing temperature…etc that maybe influence phase structure.

There were two ways to raise dielectric constant (κ) for Eq. (1). The molar polarizability (αm)could to be increased or the molar volume (Vm) might decrease. When we discussed the

same dielectric, we only considered about the Vm of various conditions. We would like to

discuss the κ-values impact on some of the lattices, ex. cubic, tetragonal, monoclinic, orthorhombic…etc. The highest κ-value is cubic phase and if the phase spectra are others, and the κ-value could reduce.

2-5.5 Structural Images of HfAlOx Films by TEM Analysis

Fig. 2-29 shows the images of cross-sectional TEM for the as-deposited HfAlOx film with Hf/Al composition ratio (~7% Al) deposited at 500℃, the samples with subsequent rapid temperature annealing at 900℃ for 30sec in N2 ambient, respectively. The total physical

(38)

19

thickness, the individual thickness of HfAlOx films was 3.6nm and interfacial layer was 1.7nm. Summary of thickness were in Table 2-6.

(39)

20

Table 2-1

Recipes of HfO

2

, HfSiOx and HfAlOx

in Aixtron atomic-vapor deposition (AVD) system.

Recipe

Chamber

/LDS

Subsector

Pressure

O

2

Flow

(sccm)

Ar

Flow

(sccm)

HfO

2

170℃

500℃

5 mbar

1300

200

HfSiOx

170℃

500℃

9 mbar

1800

200

HfAlOx

170℃

500℃

5 mbar

1300

200

(40)

21

Table 2-2

Summary of XPS extracted composition ratio of

HfO

2

、HfSiOx、HfAlOx films,

Hafnium (Hf)、Silicon (Si)、Oxygen (O)、Aluminum (Al)

deposited at 500℃ and PDA at 600℃, 24 h

HK TFT 40nm

condition

Pulse Ratio Composition Ratio

Si or Al

content

01.HfO

2

Hf/O = 1/2

1/2.3

02.HfO

2

+HfSiOx

Hf/O = 1/2

1/2.3

66% (IL)

03.HfSiOx

Hf/Si = 10/1

1/0.33

25%

04.HfSiOx

Hf/Si = 5/1

1/0.67

40%

05.HfSiOx

Hf/Si = 1/1

1/2

66%

06.HfAlOx

Hf/Al = 10/1

1/0.07

~7%

07.HfAlOx

Hf/Al = 5/1

1/0.14

12%

08.HfAlOx

Hf/Al = 1/1

1/0.67

40%

(41)

22

Table 2-3

Summary of XPS extracted composition ratio of

HfO

2

、HfSiOx、HfAlOx films,

Hafnium (Hf)、Silicon (Si)、Oxygen (O)、Aluminum (Al)

deposited at 500℃ and RTA at 900℃, 30s

OM HK 4nm

Condition

Pulse Ratio Composition Ratio

Si or Al

content

01.HfO

2

Hf/O = 1/2

1/2.3

02.HfSiOx

Hf/Si = 30/1

1/0.10

9%

03.HfSiOx

Hf/Si = 20/1

1/0.14

12%

04.HfSiOx

Hf/Si = 10/1

1/0.33

25%

05.HfSiOx

Hf/Si = 5/1

1/0.67

40%

06.HfSiOx

Hf/Si = 1/1

1/2

66%

07.HfSiOx

Hf/Si = 1/2

1/3.3

77%

08.HfAlOx

Hf/Al = 10/1

1/0.07

~7%

09.HfAlOx

Hf/Al = 5/1

1/0.14

12%

10.HfAlOx

Hf/Al = 1/1

1/0.67

40%

11.HfAlOx

Hf/Al = 1/2

1/1.67

63%

(42)

23

Table 2-4

Summary of thickness for the samples

deposited at 500℃ and PDA at 600℃, 24h

HK TFT 40nm

Condition

Physical

thickness (A)

(TEM)

Thickness of

High-k/interfacial

layer (A)

01.HfO

2

504

489/15

02.HfO

2

+HfSiOx-IL (66% Si)

445

370/65/10

(43)

24

Table 2-5

Summary of TEM-EDX composition ratio of HfO

2

+HfSiOx-IL stack structure,

Hafnium (Hf)、Silicon (Si)、Oxygen (O)

deposited at 500℃ and PDA at 600℃, 24h

Hf

Si

O

Composition Ratio

HfO

2

(Top layer)

31.58%

18.14%

50.27%

Hf/O = 1/1.6

HfSiOx-IL (66% Si)

(44)

25

Table 2-6

Summary of thickness for the samples

deposited at 500℃ and rapid temperature annealing at 900℃, 30s

OM HK 4nm

Condition

Physical

thickness (A)

(TEM)

Thickness of

High-k/interfacial

layer (A)

HfO

2

53

33/20

HfSiOx (25% Si)

46

30/16

HfAlOx (~7% Al)

53

36/17

(45)

26

Figure 2-1 Schematic diagram of atomic-vapor deposition (AVD)

system.

(46)

27 5 10 15 20 25 30 4f5/2 4f7/2 HfO2 HfO2+HfSiOx- IL In te n si ty ( A .U .)

Binding Energy (eV) Hf 4f

(a)

(b)

Figure 2-2 XPS data of (a)Hf

4f

spectra, and (b)O

1s

spectra for

HfO

2

and HfO

2

+HfSiOx-ILfilms deposited 400A

by AVD.

520 525 530 535 540 In te n si ty ( A .U .) HfO2+HfSiOx- IL HfO2

Binding Energy (eV) O 1s

(47)

28 5 10 15 20 25 30 HfO2 40A In te n si ty ( A .U .) Hf 4f

Binding Energy (eV) 4f5/2 4f7/2 520 525 530 535 540 HfO2 40A In te n si ty ( A .U .) O 1s

Binding Energy (eV)

(a)

(b)

Figure 2-3 XPS data of (a)Hf

4f

spectra, and (b)O

1s

spectra for

(48)

29 20 30 40 50 60 70 0 1000 2000 3000 4000 5000 Monoclinic (-231) (113) (131) (130) (220) (112) (102) (120) (200) (111) (-111) In te n si ty ( A .U .) 2

θ

HfO2 400A 6000C, 24h (110) 20 30 40 50 60 70 0 1000 2000 3000 4000 5000 6000 Monoclinic (131) (-231) (130) (113) (220) (112) (102) (120) (200) (111) (-111) In te n si ty ( A .U .) 2

θ

HfO2 300A+HfSiOx-IL 100A 6000C, 24h

(110)

Figure 2-4 XRD spectra of HfO

2

film deposited 400A by AVD.

PDA 600℃and 24h in N

2

ambient.

Figure 2-5 XRD spectra of HfO

2

+HfSiOx-IL films deposited 300A

(49)

30 20 30 40 50 60 70 In te n si ty ( A .U .) Monoclinic (-113) (220) (211) (102) (200) (-111) HfO2 40A RTA 9000C, 30s 2

θ

Figure 2-6 XRD spectra of HfO

2

film deposited 40A by AVD.

(50)

31

TEM

HfO

2

/IL/Poly-Si

48.9nm

Poly-Si (channel)

Poly-Si

roughness

Top

IL=1.0nm

Figure 2-7 Cross-sectional TEM images of TFTs incorporating

HfO

2

dielectric. The thickness of HfO

2

and IL are

(51)

32 HfO2 = 37 nm HfSiOx = 6.5 nm

TEM

HfO

2

+HfSiOx-IL/IL/Poly-Si

IL=1.0nm

Figure 2-8 Cross-sectional TEM images of TFTs incorporating two

dielectrics of HfO

2

+HfSiOx-IL. The thickness of HfO

2

,

HfSiOx-IL and IL are around 37nm, 6.5nm and 1.0nm,

respectively. (Spectrum 2)

Figure 2-9 TEM-EDX for composition ratios of Hf and Si from

HfO

2

dielectric on top structure of Spectrum 2.

(52)

33

Figure 2-10 Cross-sectional TEM images of TFTs incorporating

two dielectric of HfO

2

+HfSiOx-IL film. The thickness

of HfO

2

, HfSiOx-IL and IL are around 37nm, 6.5nm

and 1.0nm, respectively. (Spectrum 1)

Figure 2-11 TEM-EDX for composition ratios of Hf and Si from

HfSiOx-IL dielectric on bottom structure of Spectrum1

(53)

34

IL=2.0nm

3.3nm

Si

Figure 2-12 Cross-sectional TEM images of TFTs incorporating

HfO

2

dielectric. The thickness of HfO

2

and IL are

(54)

35 5 10 15 20 25 30 4f5/2 4f7/2 Hf/Si = 10/1 Hf/Si = 5/1 Hf/Si = 1/1 In te n si ty ( A .U .)

Binding Energy (eV) Hf 4f 90 95 100 105 110 115 Hf/Si = 10/1 Hf/Si = 5/1 Hf/Si = 1/1 In te n si ty ( A .U .)

Binding Energy (eV) Si 2p

Figure 2-13 XPS spectra of Hf

4f

for HfSiOx films deposited by

AVD at various Hf/Si composition ratios on Si (100).

Figure 2-14 XPS spectra of Si

2p

for HfSiOx films deposited by

(55)

36 520 525 530 535 540 545 In te n si ty ( A .U .)

Binding Energy (eV) O 1s Hf/Si = 1/1 Hf/Si = 5/1 Hf/Si = 10/1 20 25 30 35 40 45 50 55 60 65 70 0 1000 2000 3000 4000 5000 25% Si 40% Si 66% Si In te n si ty ( A .U .) 2

θ

HfSiOx 400A 6000C, 24h

Si rich

Figure 2-15 XPS spectra of O

1s

for HfSiOx films deposited by

AVD at various Hf/Si composition ratios on Si (100).

Figure 2-16 XRD spectra of HfSiOx films deposited by AVD.

PDA 600℃and 24h in N

2

ambient.

(56)

37

5 10 15 20 25 30

4f5/2 4f7/2

Binding Energy (eV)

HfSiOx 40A Hf 4f 9% Si 12% Si 25% Si 40% Si 66% Si 77% Si Hf In te n si ty ( A .U .) 90 95 100 105 110 115

Binding Energy (eV)

9% Si 12% Si 25% Si SiOx 102.2 eV HfSiOx 40A In te n si ty ( A .U .) Si 2p Si 97.6 eV 77% Si 66% Si 40% Si

Figure 2-17 XPS spectra of Hf

4f

for HfSiOx films deposited 40A by

AVD at various Hf/Si composition ratios on Si (100).

Figure 2-18 XPS spectra of Si

2p

for HfSiOx films deposited 40A by

(57)

38

TEM

HfSiOx /IL/Poly-Si

34.6 nm IL=1.0nm 20 30 40 50 60 70 Monoclinic + Orthorhombic (020) (131) (220) (211) 9% Si 12% Si 25% Si 40% Si 66% Si 77% Si In te n si ty ( A .U .) 2

θ

HfSiOx 40A RTA 9000C, 30s

Figure 2-19 XRD spectra of HfSiOx films deposited 40A by AVD.

RTA 900℃and 30sec in N

2

ambient.

Figure 2-20 Cross-sectional TEM images of TFTs incorporating

HfSiOx dielectric. The thickness of HfSiOx and IL are

around 34.6nm and 1.0nm, respectively.

(58)

39 5 10 15 20 25 30 4f5/2 4f7/2 Hf/Al = 10/1 Hf/Al = 5/1 Hf/Al = 1/1 In te n si ty ( A .U .)

Binding Energy (eV) Hf 4f

IL=1.6nm

3.0nm

Si

Figure 2-21 Cross-sectional TEM images of TFTs incorporating

HfSiOx dielectric. The thickness of HfSiOx and IL are

around 3.0nm and 1.6nm, respectively.

Figure 2-22 XPS spectra of Hf

4f

for HfAlOx films deposited by

(59)

40 65 70 75 80 Hf/Al = 10/1 Hf/Al = 5/1 Hf/Al = 1/1 In te n si ty ( A .U .)

Binding Energy (eV) Al 2p 520 525 530 535 540 545 Hf/Al = 10/1 Hf/Al = 5/1 Hf/Al = 1/1 In te n si ty ( A .U .)

Binding Energy (eV) O 1s

Figure 2-23 XPS spectra of Al

2p

for HfAlOx films deposited by

AVD at various Hf/Al composition ratios on Si (100).

Figure 2-24 XPS spectra of O

1s

for HfAlOx films deposited by

(60)

41 20 25 30 35 40 45 50 55 60 65 70 75 0 10000 20000 30000 40000 50000 (110) ~7% Al 12% Al 40% Al (311) (220) (200) (-111) (211) (311) (200) (220) (111)

Monoclinic (domi.) + Cubic-like phase

In te n si ty ( A .U .) 2

θ

HfAlOx 400A 6000C, 24h Cubic-like phase

Al rich

5 10 15 20 25 30 4f5/2 4f7/2 In te n si ty ( A .U .)

Binding Energy (eV) Hf 4f Hf HfAlOx 40A ~7% Al 12% Al 40% Al 63% Al

Figure 2-25 XRD spectra of HfAlOx films deposited by AVD.

PDA 600℃and 24h in N

2

ambient.

Figure 2-26 XPS spectra of Hf

4f

for HfAlOx films deposited 40A by

(61)

42 70 75 80 HfAlOx 40A ~7% Al In te n si ty ( A .U .)

Binding Energy (eV)

12% Al 40% Al 63% Al Al 2p 20 30 40 50 60 70 In te n si ty ( A .U .) Orthorhombic Monoclinic + Orthorhombic Orthorhombic (213) (420) (020) (211) HfAlOx 40A RTA 9000C, 30s 2

θ

~7% Al 12% Al 40% Al 63% Al

Figure 2-27 XPS spectra of Al

2p

for HfAlOx films deposited 40A by

AVD at various Hf/Al composition ratios on Si (100).

Figure 2-28 XRD spectra of HfAlOx films deposited 40A by AVD.

RTA 900℃and 30sec in N

2

ambient.

(62)

43

Si

IL=1.7nm

3.6nm

Figure 2-29 Cross-sectional TEM images of TFTs incorporating

HfAlOx dielectric. The thickness of HfAlOx and IL

are around 3.6nm and 1.7nm, respectively.

參考文獻

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