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研究生:蕭淑慧
研究生(外文):Shu-Hui Hsiang
論文名稱:以常壓式有機金屬化學氣相沉積方法所成長氧化鋅薄膜之歐姆接觸特性研究
論文名稱(外文):Study on the characteristics of ohmic contact to ZnO grown by atmospheric pressure MOCVD
指導教授:溫武義
指導教授(外文):Wu-Yih Uen
學位類別:碩士
校院名稱:中原大學
系所名稱:電子工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2009
畢業學年度:97
語文別:英文
論文頁數:72
中文關鍵詞:氧化鋅歐姆接觸鈦/鈀/銀鈦/金特徵接觸電阻值
外文關鍵詞:Specific contact resistance.Zinc oxideTi/Pd/AgOhmic ContactTi/Au
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氧化鋅( ZnO )為一種可應用於製備紫外光發光二極體( UV-LEDs )、太陽能電池窗戶層( window layers )與液晶顯示器( LCD )透明電極之Ⅱ-Ⅵ族化合物半導體 。在本研究中,我們利用常壓式有機金屬化學氣相沉積法於矽基板上成長出的n型氧化鋅薄膜,並在薄膜上蒸鍍金屬電極研究其歐姆接觸特性。
在實驗中使用鈦/鈀/銀與鈦/金兩種金屬組合,並且利用不同的溫度以及時間變化來得到最佳回火條件,進而求得最低的特徵電阻值。由實驗結果我們可以得知鈦/鈀/銀金屬組合在電子濃度為 8.7×1020 cm-3的n型氧化鋅薄膜之特徵電阻值為最低,並且在溫度為50℃,時間為一分鐘氮氣環境中的回火條件下,可得最低特徵電阻值 9.49×10-6 Ω-cm2。
此外在未掺雜氧化鋅薄膜之電子濃度為 2.6×1017 cm-3上使用鈦/鈀/銀金屬組合,並且在溫度為300℃時間為一分鐘時特徵電阻值為 3.49×10-4 Ω-cm2,之後再由時間變化可以得知,在相同回火溫度300℃時間縮短為30秒氮氣環境中的回火條件下,特徵電阻值則降為 5.81×10-5 Ω-cm2。接下來若改變金屬組合為鈦/金,可以得知氧化鋅薄膜在電子濃度為 8.7×1020 cm-3時,溫度為250℃時間為一分鐘氮氣環境中的回火條件下特徵電阻值為 4.93×10-6 Ω-cm2。
由上述實驗結果可以得知在n型氧化鋅薄膜之電子濃度為 8.7×1020 cm-3時特徵電阻值可以達到9.49×10-6 Ω-cm2;而於未掺雜氧化鋅薄膜下最佳條件為在氮氣環境中以300℃回火30秒的特徵電阻值最低為7.83×10-5 Ω-cm2;若改以鈦/金組合對未掺雜氧化鋅薄膜形成歐姆接觸則在回火條件為250℃時間為一分鐘於氮氣環境下時最佳特徵電阻值為 4.93×10-6 Ω-cm2。
Zinc oxide (ZnO) is a II - VI compound semiconductor, which can be used for preparing ultraviolet light-emitting diodes (UV- LEDs), the window layer of solar cell and a transparent electrode for liquid crystal display (LCD).
In this thesis, ZnO thin films were grown on silicon substrates by the atmospheric pressure chemical-vapor deposition (AP-MOCVD). On these ZnO films metal systems were deposited by E-Gun to form ohmic contacts. Two kinds of metal system: Ti (titanium) /Pd (palladium) /Ag (silver) and Ti (titanium)/Au (gold) were compared by optimizing the annealing temperature and time to obtain the minimum specific contact resistance for both systems.
Conclusively, a lowest specific contact resistance to the n-ZnO of electron concentration = 8.7×1020 cm-3 formed by the Ti/Pd/Ag metal system is 9.49×10-6 Ω-cm2 with a sintering conducted at 50℃ for 1 min in N2 ambient.
Otherwise, a lowest specific contact resistance of Ti/Pd/Ag metal system formed on an un-doped ZnO film of electron concentration = 2.6×1017 cm-3 is 5.81×10-5 Ω-cm2 achieved by performing the sintering at 300℃ for 30 sec in N2 ambient.
Finally, when the metal system of Ti/Au was used to substitute Ti/Pd/Ag for forming ohmic contact to the n-ZnO of electron concentration = 8.7×1020 cm-3 a further reduced specific contact resistance of 4.93×10-6 Ω-cm2 was obtained by conducting the sintering at 250℃ for 1 min and in N2 ambient. It can be understood that the Ti/Au metal system can be used to form a good ohmic contact to the heavily doped ZnO with a low specific contact resistance.
Content

Abstract (Chinese) I
Abstract (English) III
Acknowledgment V
Content VI
Figure Captions VIII
List of Tables XII
Chapter 1 Introduction 1
Chapter 2 Theory 3
2.1 Metal Organic Chemical-Vapor Deposition 3
2.1.1 Atmospheric pressure chemical-vapor deposition (APMOCVD) 4
2.2 Metal-semiconductor contact 6
2.3 Ohmic contact mechanisms 11
2.3.1 Thermion-emission 11
2.3.2 Field tunneling emission 12
2.3.3 Thermion-field emission 13
2.4 Transmission line method (TLM) 15
2.5 Measurements 20
Chapter 3 Experimental 23
3.1 ZnO Film Growths Experimental 23
3.1.1 Wafer Clean Process 23
3.1.2 Ga-doped ZnO films deposited on Si (111) various doping densities 23
3.1.3 Undoped ZnO films deposited on Si (111) various doping densities 24
3.2 Ti/Pd/Ag and Ti/Au TLM Mode Method Process 25
3.2.1 Sample Clean 25
3.2.2 Photolithography 25
3.3 Metal Deposition 26
3.3.1 Ti/Pd/Ag metal deposition 26
3.3.2 Ti/Au metal deposition 26
3.4 The sample annealing and specific contact resistance analysis 30
3.5 Auger Electron Spectrometer; AES 30
Chapter 4 Results and Discussion 35
4.1 ZnO film growth of the SEM 35
4.2 Specific contact resistance analysis 39
4.2.1 Ti/Pd/Ag on ZnO: Ga 39
4.2.2 Ti/Pd/Ag on un-doped ZnO 45
4.2.3 Ti/Pd/Ag on undoped ZnO of AES analyze 47
4.2.4 Ti/Au on ZnO: Ga 49
Cheaper 5 Conclusions 55
Reference 57






Figure Captions

Fig.2.1 AP-MOCVD system………………...………………………….5
Fig.2.2 Energy-band diagram of a metal and semiconductor before contact……………………………………...…………………………….8
Fig.2.3 Ideal energy-band diagram of a metal-n-semiconductor junction for ψm<ψs …………………………………………………….9
Fig.2.4 Ideal energy-band diagram of a metal-n-semiconductor junction for ψm>ψs ……………………………………………………9
Fig.2.5 Ideal energy-band diagram of a metal-p-semiconductor junction for ψm>ψs ..…………………………………………………10
Fig.2.6 Ideal energy-band diagram of a metal-p-semiconductor junction for ψs>ψm …………………………………………………..10
Fig.2.7 Metal-semiconductor contact mechanism: thermion emission...................................................................................................12
Fig.2.8 Metal-semiconductor contact mechanism: field tunneling emission………………………...………………………………………13
Fig.2.9 Metal-semiconductor contact mechanism: thermion-field emission………………………...………………………………………14
Fig.2.10 TLM pattern: circular contacts......................................…...16
Fig.2.11 TLM pattern: square contacts………...…………………....16
Fig.2.12 TLM pattern: rectangular strip contacts…………….…….17
Fig.2.13 Current flow between the metal pads………...…...……….17
Fig.2.14 Equivalent circuit of TLM………………………………….19
Fig.2.15 TLM is separated by increasing distances……...………….21
Fig.2.16 Plot of measured resistance as a function contact separation………………………………………………………………22
Fig.3.1 Wafer clean…………………………..………………………..27
Fig.3.2 First photolithograph………………………………………...28
Fig.3.3 Metal evaporation……….……………………………………29
Fig.3.4 TLM model…………………………...……………………….30
Fig.3.5 Flow chart for metal-semiconductor ohmic contact formation.................................................................................................31
Fig.3.6 Rapid Thermal Annealing Systems…………………………..32
Fig.3.7 I-V measurements (HP-4155)…..…………………………….33
Fig.3.8 I-V measurements……………………..……………………...34
Fig.4.1 SEM images of ZnO: Ga films deposited with different TEG flow rates: (a) 2, (b) 4 sccm……………………...…………………….36
Fig.4.1 SEM images of ZnO: Ga films deposited with different TEG flow rates: (c) 6, (d) 8 sccm…………………………………...……….37
Fig.4.1 SEM images of ZnO: Ga films deposited with different TEG flow rates: (e) 10, (f) 12 sccm………………………………...………..38
Fig.4.2 SEM images of undoped ZnO film…………………….…….39
Fig.4.3 Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/Ag(100 nm) on ZnO: Ga (TEG= 2 sccm) after annealing at different temperature for 1min………….……………………………41
Fig.4.4 Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/ Ag(100 nm) on ZnO: Ga (TEG= 4 sccm) after annealing at different temperature for 1min…………………………….…………41
Fig.4.5 Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/ Ag(100 nm) on ZnO: Ga (TEG= 6 sccm) after annealing at different temperature for 1min…………….…………………………42
Fig.4.6 Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/ Ag(100 nm) on ZnO: Ga (TEG= 8 sccm) after annealing at different temperature for 1min…………………………….…………42
Fig.4.7 Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/ Ag(100 nm) on ZnO: Ga (TEG= 10 sccm) after annealing at different temperature for 1min…………………………………….…43
Fig.4.8Variation of specific contact resistance for Ti(50 nm)/ Pd(70 nm)/ Ag(100 nm) on ZnO: Ga (TEG= 12 sccm) after annealing at different temperature for 1min…………………………………….…43
Fig.4.9 The concentration compare with variation annealing temperature.......................................................................…………….44
Fig.4.10 Specific contact resistively of Ti/Pd/Ag contact to un-doped ZnO thin films treated by RTA at various temperatures and for time duration of 60 sec……………………………………………...……….45
Fig.4.11 Specific contact resistance of Ti/Pd/Ag contact to un-doped ZnO thin films treated by RTA at 300°C and for different time durations.................................................................…………………….46
Fig.4.12 AES depth profiles for the Ti/Pd/Ag samples as a function of the annealing temperature. (a) as-deposited (b) 300 and (c) 500°C………………………………………………………………..…..48
Fig.4.13 Variation of specific contact resistance for Ti (30 nm)/ Au(50 nm) on ZnO: Ga (TEG= 2 sccm) after annealing at different temperature for 1min……………………………….…………………50
Fig.4.14 Variation of specific contact resistance for Ti(30 nm)/Au (50 nm) on ZnO: Ga (TEG= 4 sccm) after annealing at different temperature for 1min……………………………...…………………..51
Fig.4.15 Variation of specific contact resistance for Ti(30 nm)/ Au(50 nm) on ZnO: Ga (TEG= 6 sccm) after annealing at different temperature for 1min…………………………….................................51
Fig.4.16 Variation of specific contact resistance for Ti(30 nm)/ Au(50 nm) on ZnO: Ga (TEG= 8 sccm) after annealing at different temperature for 1min………………………………...………………..52
Fig.4.17 Variation of specific contact resistance for Ti(30 nm)/ Au(50 nm) on ZnO: Ga (TEG= 10 sccm) after annealing at different temperature for 1min………………………………………………….52
Fig.4.18 Variation of specific contact resistance for Ti(30 nm)/ Au(50 nm) on ZnO: Ga (TEG= 12 sccm) after annealing at different temperature for 1min…………………………...……………………..53

















List of Tables

Table 2.1 Work function of metals……………………………………..7
Table 2.2 Electron affinity of semiconductors…………………………8
Table 4.1 Variation of the flow rate and annealing temperature for specific contact resistance of Ti/Pd/Ag metal structure……….…….44
Table 4.2 Variation of flow rate and annealing temperature for specific contact resistance of Ti/Au metal structure………..………..54
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